JP7630251B2 - Sewage treatment device and sewage treatment method - Google Patents

Description

The present invention relates to a wastewater treatment device and a wastewater treatment method.

Conventionally, there has been known a wastewater treatment apparatus that includes a reaction tank for biologically treating wastewater, a membrane separation device that is immersed in the reaction tank and removes solids from the biologically treated wastewater, and an aeration pipe that is installed below the membrane separation device and supplies air or other gas to the membrane separation device. The biological treatment of wastewater in the reaction tank is carried out based on, for example, the activated sludge method, in which wastewater is treated with organic sludge that contains microorganisms, i.e., so-called activated sludge.

Specifically, in the activated sludge process, a nitrification reaction is carried out in the presence of oxygen (aerobic conditions) to convert ammonia into nitrite and nitrate. In addition, a denitrification reaction is carried out to convert the nitrite and nitrate converted from ammonia by the nitrification reaction into nitrogen. Unlike the nitrification reaction which is carried out in the presence of oxygen (aerobic conditions), the denitrification reaction must be carried out in an anoxic state. The denitrification reaction may be carried out in a reaction tank different from the reaction tank in which the nitrification reaction is carried out, but in order to reduce the space required for the sewage treatment device, a sewage treatment device has been proposed in which the nitrification reaction and the denitrification reaction are carried out in a single reaction tank (see, for example, Patent Documents 1 to 3).

Figure 8 is a schematic diagram of a conventional wastewater treatment device. The wastewater treatment device in Figure 8 includes a reaction tank 1 in which a nitrification reaction in an aerobic state and a denitrification reaction in an anaerobic state are performed, and a raw water tank 9 for supplying wastewater to the reaction tank 1. The reaction tank 1 has a partition plate 7 for dividing the reaction tank 1 into a plurality of compartments. Specifically, the reaction tank 1 is divided into a wastewater area A surrounded by the partition plate 7 and a wastewater area B surrounded by the partition plate 7 and the inner wall of the reaction tank 1, and the wastewater area A has a membrane separation device 2 and an aeration pipe 4. The reaction tank 1 also has a wastewater supply start water level LWL (Low water level) for starting the supply of wastewater from the raw water tank 9, and a wastewater supply stop water level HWL (High water level) for stopping the supply of wastewater from the raw water tank 9, and the upper end of the partition plate 7 is located between the wastewater supply start water level LWL and the wastewater supply stop water level HWL.

In the wastewater treatment device of Fig. 8, the supply of wastewater from the raw water tank 9 is started when the water level in the reaction tank 1 reaches the wastewater supply start water level LWL, and the supply of wastewater from the raw water tank 9 is stopped when the water level reaches the wastewater supply stop water level HWL, so that the wastewater level changes. As a result, the wastewater level moves between a position higher than the upper end of the partition plate 7 (hereinafter referred to as the "sewage overflow position") and a position lower than the upper end of the partition plate 7 (hereinafter referred to as the "sewage non-overflow position").
FIG. 9 is a diagram showing a schematic flow of wastewater when the wastewater level in the reaction tank 1 in FIG. 8 is at the wastewater overflow position.

When the wastewater level is at the wastewater overflow position, the air supplied from the air diffuser 4 to the membrane separation device 2 causes the wastewater to overflow the upper end of the partition plate 7, forming a circulating flow around the partition plate 7. This circulating flow causes the nitrite and nitrate in the wastewater area A to move to the wastewater area B, and most of the air in the wastewater area A is released outside the reaction tank 1 without moving to the wastewater area B. In other words, when the circulating flow is formed, a nitrification reaction takes place in the wastewater area A, which converts ammonia into nitrite and nitrate in the presence of oxygen, and a denitrification reaction takes place in the wastewater area B, which converts the nitrite and nitrate that have moved from the wastewater area on the circulating flow into nitrogen.

On the other hand, when the wastewater level is at the wastewater non-overflow position, the flow of wastewater is interrupted between wastewater area A and wastewater area B, so even if the air diffuser 4 supplies air to the membrane separation device 2, no circulating flow is formed around the partition plate 7. That is, in wastewater area A, a nitrification reaction takes place in which ammonia is converted into nitrite and nitrate in the presence of oxygen, while in wastewater area B, a denitrification reaction takes place in which the nitrite and nitrate that moved from wastewater area A before the flow of wastewater was interrupted are converted into nitrogen.

In conventional wastewater treatment equipment like that shown in Figure 8, in order to achieve good denitrification efficiency, the wastewater overflow time period and overflow stop time period were set to about 5 to 10 minutes each, and operation was repeated at intervals of 10 to 20 minutes including the overflow time period and overflow stop time period. In addition, in the reaction tank 1, the volume ratio of the wastewater area A, which is the aerobic zone, to the wastewater area B, which is the anoxic zone, was set and fixed at about 1:1 to 1:2.

Furthermore, depending on the size of the sewage treatment plant, the amount of sewage inflow can vary greatly from day to day. For example, in a small sewage treatment plant, the amount of sewage inflow during high load times is two to three times the amount during average treatment times, while the amount of sewage inflow during low load times drops significantly, to about 10 to 20% of the amount during average times.

JP 2004-261711 A International Publication No. 2018/123647 International Publication No. 2018/198422

However, in conventional wastewater treatment equipment (Figure 8), the combined interval between the overflow period and the overflow stop period was short, so the wastewater area B could not reach the anaerobic state required for phosphorus removal from the anoxic state, and phosphorus could not be sufficiently removed. In addition, in conventional wastewater treatment equipment, the volume ratio of the aerobic zone to the anaerobic zone was fixed, so even if the ratio of the wastewater overflow period to the overflow stop period and the air volume sent by the auxiliary aeration means were adjusted, it was not possible to adequately respond to daily flow rate fluctuations (load fluctuations).

The present invention aims to provide a wastewater treatment device and a wastewater treatment method that can simultaneously remove nitrogen and phosphorus from wastewater and perform stable wastewater treatment even when the wastewater flow rate fluctuates.

In order to achieve the above object, the sewage treatment device of the present invention is provided with a membrane separation device for separating pollutants contained in the sewage within a reaction tank for treating the sewage, and an aeration pipe for supplying air bubbles to the membrane separation device, wherein the reaction tank is provided with a first partition plate that divides the inside of the reaction tank into an area where the membrane separation device is disposed and an area where the membrane separation device is not disposed and that is disposed at a distance from the bottom of the reaction tank, and a second partition plate that has an upper end higher than an upper end of the first partition plate and that is disposed at a distance from the bottom of the reaction tank in the area where the membrane separation device is not disposed. The reaction tank has a first partition plate, a first region in which the membrane separation device is disposed, a second region existing between the first partition plate and the second partition plate, and a third region surrounded by the second partition plate and the inner wall of the reaction tank, and is characterized in that when the water level of the wastewater in the reaction tank is at a position higher than the upper end of the first partition plate, the wastewater flows from the first region over the upper end of the first partition plate and transfers to the second region, and when the water level of the wastewater in the reaction tank is at a position higher than the upper end of the second partition plate, the wastewater flows from the second region over the upper end of the second partition plate and transfers to the third region .

In order to achieve the above object, the wastewater treatment method of the present invention is a wastewater treatment apparatus including, inside a reaction tank for treating wastewater, a membrane separation device for separating pollutants contained in the wastewater, and an aeration pipe for supplying air bubbles to the membrane separation device, wherein the reaction tank includes a first partition plate that divides the inside of the reaction tank into an area where the membrane separation device is disposed and an area where the membrane separation device is not disposed and that is disposed away from the bottom of the reaction tank , a second partition plate that has an upper end higher than an upper end of the first partition plate and is disposed away from the bottom of the reaction tank in the area where the membrane separation device is not disposed, a first area where the membrane separation device is disposed, and a second area that exists between the first partition plate and the second partition plate. and a third region surrounded by the second partition and the inner wall of a reaction tank, the method for treating wastewater using the wastewater treatment device is characterized by having a first overflow step in which, when the water level of the wastewater in the reaction tank is higher than the upper end of the first partition, the wastewater flows from the first region over the upper end of the first partition and transfers to the second region , a non-overflow step in which, when the water level of the wastewater in the reaction tank is lower than the upper end of the first partition, the wastewater does not exceed the first partition, and a second overflow step in which, when the water level of the wastewater in the reaction tank is higher than the upper end of the second partition, the wastewater flows from the second region over the upper end of the second partition and transfers to the third region .

According to the present invention, it is possible to simultaneously remove nitrogen and phosphorus from wastewater, and to perform stable wastewater treatment even when the wastewater flow rate fluctuates.

1A and 1B are a top view (upper view) and a side view (lower view) that generally show a wastewater treatment device according to a first embodiment of the present invention. 2 is a side view showing a schematic diagram of the flow of wastewater when the wastewater level in the reaction tank in FIG. 1 is at the wastewater overflow position of the first partition plate 7a. FIG. 2 is a side view showing a schematic diagram of the flow of wastewater when the wastewater level in the reaction tank in FIG. 1 is at the wastewater overflow position of the second partition plate 7b. FIG. FIG. 2 is a side view that shows, in schematic form, the flow of wastewater when the wastewater level in the reaction tank in FIG. 1 is at the wastewater overflow position of the second partition plate 7b and when the wastewater is aerated by the auxiliary aeration device 5b in the second zone Z2. FIG. 5 is a top view illustrating a sewage treatment device according to a second embodiment of the present invention. FIG. 11 is a top view illustrating a wastewater treatment device according to a third embodiment of the present invention. FIG. 13 is a top view illustrating a wastewater treatment device according to a fourth embodiment of the present invention. FIG. 1 is a schematic diagram of a conventional wastewater treatment device. FIG. 9 is a side view showing a schematic diagram of the flow of wastewater when the wastewater level in the reaction tank in FIG. 8 is at the wastewater overflow position.

The first embodiment of the present invention will be described in detail below with reference to the drawings.

Figure 1 (lower diagram) is a side view that shows a schematic diagram of a wastewater treatment device according to an embodiment of the present invention.

The wastewater treatment device in Figure 1 (lower diagram) is equipped with a single-tank reaction tank 1 for biologically treating wastewater. The reaction tank 1 is rectangular and is constructed by joining four tank walls and a bottom surface made of rectangular plate-shaped members so that they are perpendicular to each other. The reaction tank 1 has a membrane separation device 2 that separates pollutants contained in the wastewater, an aeration pipe 4 that supplies air bubbles to the membrane separation device 2, a first partition plate 7a, and a second partition plate 7b. The membrane separation device 2 is connected to a suction pump 3 outside the reaction tank 1. When the suction pump 3 is driven, the biologically treated wastewater is filtered by the membrane separation device 2, and the filtered water is taken out of the reaction tank 1.

The aeration pipe 4 is installed at the bottom of the membrane separation device 2 and is connected to a blower (not shown) outside the reaction tank 1, and the blower supplies air to the aeration pipe 4. Since the membrane separation device 2 filters wastewater, sludge substances in the wastewater adhere to the membrane surface of the membrane separation device 2. If the sludge substances in the wastewater adhering to the membrane surface of the membrane separation device 2 are left as they are, the membrane separation device 2 will become clogged and will not be able to properly filter the wastewater. However, air supplied from the blower to the aeration pipe 4 is supplied to the membrane surface of the membrane separation device 2, preventing sludge substances from adhering to the membrane surface of the membrane separation device 2.

The first partition plate 7a divides the inside of the reaction tank 1 into an area where the membrane separation device 2 is placed and an area where the membrane separation device 2 is not placed. The second partition plate 7b is placed between the first partition plate 7a and the inner wall of the reaction tank, and the area where the membrane separation device 2 is not placed is divided into two areas by the second partition plate 7b. The second partition plate 7b has an upper end higher than the upper end of the first partition plate 7a, and the difference between the upper end of the second partition plate 7b and the upper end of the first partition plate 7a is usually 3 to 50 cm, and preferably 5 to 30 cm. Since the wastewater treatment device of this embodiment has two partition plates (baffles), it is also called a double baffled membrane bioreactor (2B-MBR). The first partition plate 7a and the second partition plate 7b are placed away from the bottom of the reaction tank 1. The partition plate is required to be durable, so it is made of a metal such as stainless steel. The arrangement of the first partition plate 7a and the second partition plate 7b in the reaction tank 1 can be in various forms, as shown in Figures 5 to 7 below.

The first partition plate 7a and the second partition plate 7b may have a height adjustment means at the upper end capable of adjusting the height. The height adjustment means may be a rectangular plate-like member fixed to the upper end of the partition plate using a plurality of fixing members, and a movable weir that can slide up and down. It may also be a rectangular plate-like member fixed to the upper end of the partition plate via a hinge member or the like, and the means for adjusting the height of the upper end of the partition plate by tipping the plate-like member. When such a height adjustment means is attached to the partition plate, it is not necessary to provide a difference in the height of the upper ends between the first partition plate 7a and the second partition plate 7b, and it is sufficient that the upper end of the height adjustment means installed at the upper end of the second partition plate 7b is positioned higher than the upper end of the first partition plate 7a.

FIG. 1 (upper figure) is a top view of the sewage treatment device of FIG. 1 (lower figure).
The first partition plate 7a and the second partition plate 7b each consist of four rectangular plate-shaped members. The first partition plate 7a surrounds the entire periphery of the membrane separation device 2, and the second partition plate 7b surrounds the entire periphery of the first partition plate 7a. By providing the first partition plate 7a and the second partition plate 7b, the reaction tank 1 is divided into a first region Z1 in which the membrane separation device is disposed, a second region Z2 surrounded by the first partition plate and the second partition plate, and a third region Z3 surrounded by the second partition plate and the inner wall of the reaction tank. The volume ratio of the first region, the second region, and the third region can be optimally selected according to the inflow load and the treatment target, but it is preferable that it is 1:1 to 2:0.2 to 1 for general sewage.

The wastewater treatment device in FIG. 1 (lower diagram) is equipped with a wastewater supply means for supplying wastewater to the third zone Z3. The reaction tank 1 is connected to a raw water tank (not shown) that stores raw water via a raw water pump 6, and when the raw water pump 6 is driven, the wastewater to be treated is supplied from the raw water tank to the third zone Z3 in the reaction tank 1 by the wastewater supply means.

In the first zone Z1, an auxiliary aeration means 5a is disposed on the side of the lower part of the membrane separation device (Figure 1 (lower diagram)). When the amount of oxygen supplied by the aeration tube 4 is insufficient, the amount of oxygen can be supplemented by aeration from the auxiliary aeration means 5a. In addition, in the second zone Z2, an auxiliary aeration means 5b is disposed. By aeration from the auxiliary aeration means 5b, for example, during high load periods described below, the second zone can be made into an aerobic state and aerobic treatment can be performed. The auxiliary aeration means 5a and 5b are each connected to a blower (not shown), and air is supplied from the blower.

The wastewater in the reaction tank 1 contains nitrifying bacteria for carrying out nitrification reactions, denitrifying bacteria for carrying out denitrification reactions, and phosphorus accumulating bacteria for releasing and ingesting phosphorus in order to treat the wastewater. The denitrifying bacteria are, for example, denitrifying bacteria such as Pseudomonas denitrificans and Paracox denitrificans, or heterotrophic bacteria that do not operate in aerobic conditions but carry out denitrification reactions in anaerobic conditions. The phosphorus accumulating bacteria are, for example, polyphosphate accumulating bacteria.

Figure 2 is a side view that shows the schematic flow of wastewater when the water level in the reaction tank in Figure 1 is at the wastewater overflow position of the first partition plate 7a.

When the water level in the reaction tank 1 is at the wastewater overflow position of the first partition plate 7a (the position between WL1 (Water Level 1) and WL2 (Water Level 2) in Figure 1 (lower diagram)), air is supplied from the air diffuser 4 to the membrane separation device 2, causing the wastewater to overflow the upper end of the partition plate 7a from the first area Z1 and move to the second area Z2 outside the partition plate 7a (Figure 2). The wastewater then descends in the second area Z2, passes through the area below the partition plate 7a, and returns to the first area Z1 inside the partition plate 7a. In other words, when the water level of the wastewater is at the wastewater overflow position of the first partition plate 7a and the wastewater overflows the partition plate 7a, a circulating flow is formed that circulates around the partition plate 7a. When the circulation flow is formed, for example, nitrite and nitrate in the first zone Z1 move to the second zone Z2, and most of the air in the first zone Z1 is released to the outside of the reaction tank 1 without moving to the second zone Z2. At this time, in the first zone Z1 (aerobic zone), a nitrification reaction that converts ammonia to nitrite and nitrate in the presence of oxygen progresses, and in the second zone Z2 (anoxic zone), a denitrification reaction that converts the nitrite and nitrate that have moved from the first zone Z1 on the circulation flow to nitrogen progresses.

On the other hand, when the wastewater level is at the wastewater non-overflow position (lower than WL1 in Figure 1 (lower diagram)) and the flow of wastewater is interrupted between the first zone Z1 and the second zone Z2, even if the air diffuser 4 supplies air to the membrane separation device 2, a circulation flow is not formed around the partition plate 7a. Therefore, in the first zone Z1 (aerobic zone), a nitrification reaction that converts ammonia to nitrite and nitrate in the presence of oxygen proceeds, and in the second zone Z2 (anoxic zone), a denitrification reaction that converts the nitrite and nitrate that moved from the first zone Z1 before the flow of wastewater was interrupted to nitrogen proceeds.

FIG. 3 is a side view that shows a schematic view of the flow of wastewater when the water level in the reaction tank in FIG. 1 is at the wastewater overflow position of the second partition plate 7b.
When the water level in the reaction tank 1 is at the wastewater overflow position of the second partition plate 7b (a position higher than WL2 in FIG. 1 (lower diagram)), a circulation flow is formed circulating around the partition plate 7a, similar to when the wastewater level is at the wastewater overflow position of the first partition plate 7a (between WL1 and WL2) (FIG. 2). At this time, in the first zone Z1 (aerobic zone), a nitrification reaction proceeds in which ammonia is converted to nitrite and nitrate in the presence of oxygen, and in the second zone Z2 (anoxic zone), a denitrification reaction proceeds in which nitrite and nitrate transferred from the first zone Z1 on the circulation flow are converted to nitrogen.

Furthermore, in FIG. 3, the wastewater that has overflowed the upper end of the partition plate 7a from the first zone Z1 also migrates to the third zone Z3 outside the partition plate 7b. The wastewater that has migrated to the third zone Z3 then descends within the third zone Z3, passes through the zone below the partition plate 7b, and returns to the first zone Z1 inside the partition plate 7a. That is, when the wastewater level is at the wastewater overflow position of the second partition plate 7b, a circulation flow that circulates between the first zone Z1 and the third zone Z3 is formed in addition to a circulation flow that circulates between the first zone Z1 and the second zone Z2. At this time, an anaerobic state is formed in the third zone Z3.

In the present invention, an aerobic state refers to a state in which oxygen molecules are dissolved in wastewater, an anaerobic state refers to a state in which oxygen molecules are not dissolved in wastewater but bound oxygen is dissolved in the form of nitrate or nitrite, and an anaerobic state refers to a state in which neither oxygen molecules nor bound oxygen are dissolved. The anaerobic state and the anoxic state can be confirmed or distinguished by, for example, measuring the dissolved oxygen concentration and nitrate concentration in the wastewater using a dissolved oxygen meter or a nitrate meter.

3, the anaerobic compartment of the third zone Z3 and the anoxic compartment of the second zone Z2 can be formed by setting the ratio of the circulating water volume of the third zone Z3 to the circulating water volume of the second zone Z2, i.e., the ratio of the overflow water volume of the second partition plate 7b to the overflow water volume of the first partition plate 7a, to 1:1 to 1:10, preferably 1:3 to 1:5. The overflow water volume of the partition plate is determined by the product (overflow cross-sectional area) of the overflow water depth (difference between the water level and the upper end of the partition plate) and the overflow weir length (length of the partition plate). Therefore, by appropriately setting the upper end position and length of the partition plates 7a and 7b in the reaction tank 1 and further adjusting the water level in the reaction tank 1, the anaerobic compartment (Z3) and the anoxic compartment (Z2) can be formed. In addition, the raw water supplied to the third zone Z3 by the wastewater supply means contains organic matter and ammonia, which consume oxygen, and the consumption of oxygen by these organic matter and ammonia also contributes to the formation of an anaerobic state.

In FIG. 3, in the third zone Z3 (anaerobic section), a process for biologically removing phosphorus is carried out. Specifically, raw water is supplied to the third zone Z3 by a wastewater supply means, and the raw water contains organic matter that consumes oxygen, ammonia, phosphorus, etc. In addition, the wastewater that flows over the upper end of the partition plate 7b and moves to the third zone Z3 contains activated sludge containing phosphorus-accumulating bacteria, and in the third zone Z3, which is in an anaerobic state, the phosphorus-accumulating bacteria take in organic matter and release phosphorus. The wastewater in which the amount of dissolved phosphorus has increased due to the metabolism of the phosphorus-accumulating bacteria in the third zone returns to the first zone Z1 inside the partition plate 7a through the zone below the second partition plate 7b.

In the first zone Z1 (aerobic zone), the phosphorus accumulating bacteria take in an excess of phosphorus, more than the amount released in the third zone Z3 (anaerobic zone). In other words, the phosphorus accumulating bacteria take in more phosphorus than they once released, and the phosphorus content in the bacteria increases. Wastewater containing phosphorus accumulating bacteria that have taken in an excess amount of phosphorus can be separated into sludge containing phosphorus accumulating bacteria using membrane separation device 2, thereby removing the phosphorus from the wastewater.

The level of the wastewater in the reaction tank 1 is generally changed by changing the amount of raw water supplied from the raw water tank to the reaction tank 1 by the wastewater supply means, but the amount of suction through the membrane may also be changed. Furthermore, the wastewater treatment device of this embodiment may have a water level control means for adjusting the water level in the reaction tank 1. An example of the water level control means is a liquid level sensor that detects the water level in the reaction tank 1, i.e., the position of the liquid surface. When the liquid level sensor detects the water level of the wastewater, the raw water pump 6 automatically controls the amount of raw water supplied to the reaction tank 1 by the wastewater supply means.

In this embodiment, the daily treatment time periods can be pre-divided into, for example, normal load time periods (11:00-18:00, 23:00-2:00), high load time periods (8:00-11:00, 18:00-23:00), and low load time periods (23:00-8:00) based on daily flow rate fluctuations of the wastewater supplied to the wastewater treatment device.

The high-load time periods and low-load time periods can be set based on measured values selected from the sewage inflow volume and sewage quality, or on calculated values obtained from the measured values. Specifically, using the hourly value of the sewage inflow volume, for example, a low-load time period can be set to 0.5 times or less of the hourly value of the daily average sewage volume, a normal-load time period can be set to 0.5 to 1.5 times, and a high-load time period can be set to 1.5 times or more. In addition to the sewage inflow volume, concentration data on sewage quality, such as BOD (biological oxygen demand), COD (chemical oxygen demand), and SS (suspended solids), can be obtained, and the product of the sewage inflow volume and sewage quality (concentration) can be used to set the load time periods from the ratio to the daily average load volume as described above.

In treatment plants that automatically measure the amount of sewage inflow and the quality of sewage, the load classification is determined by the product of the amount of sewage inflow and the quality (concentration) of sewage, depending on the ever-changing inflow load, and operation can be carried out according to the load classification. In the previous example, three load classifications were shown, but it is also possible to set more classifications and perform sewage treatment.

Next, we will explain the wastewater treatment method performed by the wastewater treatment device (Figure 1) according to the first embodiment of the present invention.

As described above, the wastewater treatment device of this embodiment has a membrane separation device 2, an aeration pipe 4, a first partition plate 7a, and a second partition plate 7b inside the reaction tank 1. The membrane separation device 2 is connected to a suction pump 3 outside the reaction tank 1, and the aeration pipe 4 is connected to a blower (not shown) outside the reaction tank 1 (Figure 1 (lower figure)). The first partition plate 7a and the second partition plate 7b divide the wastewater treatment device into a first area Z1 where the membrane separation device is located, a second area Z2 surrounded by the first partition plate and the second partition plate, and a third area Z3 surrounded by the second partition plate and the inner wall of the reaction tank.

When the raw water pump 6 is driven, raw water is supplied to the third zone Z3 of the reaction tank 1 by the wastewater supply means. The wastewater supplied to the inside of the reaction tank 1 contains activated sludge including nitrifying bacteria, denitrifying reaction-performing bacteria (denitrifying bacteria), and phosphorus-accumulating bacteria, and the wastewater is biologically treated by these bacteria. When the blower is driven, air bubbles are supplied from the air diffuser 4 installed at the bottom of the membrane separation device 2. When the suction pump 3 is driven, the biologically treated wastewater is filtered by the membrane separation device 2, and the filtered water is sucked by the suction pump 3 and taken out of the reaction tank 1. At this time, the air supplied to the membrane separation device 2 from the air diffuser 4 collides with the membrane surface of the membrane separation device 2, preventing sludge material and the like from adhering to the membrane surface.

(Normal load period)
The following describes a method for treating wastewater during normal load periods when the amount of wastewater flowing into the reaction tank 1 is an average amount.
First, the water level of the wastewater in the reaction tank 1 is set to the wastewater overflow position of the first partition plate 7a, that is, the position where the wastewater overflows the first partition plate 7a but does not overflow the second partition plate 7b (the position between WL1 and WL2 in FIG. 1 (lower drawing)), and wastewater treatment is performed in this state for 7.5 minutes (first overflow step). At this time, air is supplied from the air diffuser 4 to the membrane separation device 2, so that the wastewater overflows the upper end of the partition plate 7a from the first zone Z1 and moves to the second zone Z2 outside the partition plate 7a. After that, the wastewater descends in the second zone Z2, passes through the zone below the partition plate 7a, and returns to the first zone Z1 inside the partition plate 7a, forming a circulation flow circulating around the partition plate 7a (FIG. 2). When the circulating flow is formed, a nitrification reaction takes place in the first zone Z1 (aerobic zone) in which ammonia is converted into nitrite and nitrate in the presence of oxygen, and a denitrification reaction takes place in the second zone Z2 (anaerobic zone) in which the nitrite and nitrate that have migrated from the first zone Z1 via the circulating flow are converted into nitrogen.

Then, the wastewater level in the reaction tank 1 is set to the wastewater non-overflow position of the first partition plate 7a (a position lower than WL1 in Figure 1 (lower diagram)), and wastewater treatment is performed in this state for 7.5 minutes (non-overflow step). At this time, the flow of wastewater is interrupted between the first zone Z1 and the second zone Z2, and no circulation flow is formed around the partition plate 7a. Therefore, in the first zone Z1 (aerobic zone), a nitrification reaction that converts ammonia to nitrite and nitrate in the presence of oxygen proceeds, and in the second zone Z2 (anoxic zone), a denitrification reaction that converts the nitrite and nitrate that moved from the first zone Z1 before the flow of wastewater was interrupted to nitrogen proceeds.

As described above, operation with the first partition plate 7a in the wastewater overflow position (7.5 minutes) and operation with the first partition plate 7a in the wastewater non-overflow position (7.5 minutes) are combined to form one interval (15 minutes), and operation is performed for three intervals (45 minutes). This allows the nitrification reaction in the first zone Z1 and the denitrification reaction in the second zone Z2 to proceed efficiently.

Then, the wastewater level in the reaction tank 1 is set to the wastewater overflow position of the second partition plate 7b (a position higher than WL2 in Figure 1 (lower diagram)), and wastewater treatment is carried out in this state for 5 minutes (second overflow step). At this time, the wastewater that has overflowed the upper end of the partition plate 7a from the first zone Z1 also moves to the third zone Z3 outside the partition plate 7b. Therefore, in addition to the circulation flow that circulates between the first zone Z1 and the second zone Z2, a circulation flow that circulates between the first zone Z1 and the third zone Z3 is formed (Figure 3). At this time, an anaerobic section is formed in the third zone Z3.

In the third zone Z3 (anaerobic zone), phosphorus accumulating bacteria contained in the wastewater take in organic matter and release phosphorus. In the third zone, the wastewater in which the amount of dissolved phosphorus has increased due to the metabolism of phosphorus accumulating bacteria returns to the first zone Z1 inside the partition plate 7a through the zone below the second partition plate 7b. In the first zone Z1 (aerobic zone), the phosphorus accumulating bacteria take in an excess of phosphorus beyond the amount released in the third zone Z3 (anaerobic zone). In other words, the phosphorus accumulating bacteria take in more phosphorus than they once released, so the phosphorus content in the bacteria increases. The wastewater containing phosphorus accumulating bacteria that have taken in an excess amount of phosphorus is separated from the sludge containing phosphorus accumulating bacteria by the membrane separation device 2, and the phosphorus in the wastewater is removed.

As described above, during normal load times, the first area is an aerobic zone, the second area is an anaerobic zone, and the third area is an anaerobic zone, making it possible to simultaneously remove nitrogen and phosphorus from wastewater.

(High load period)
The following describes a method for treating wastewater during high-load periods when the amount of wastewater flowing into the reaction tank 1 is large and the inflow load is high.

During high load times, the inflow of raw water containing ammonia is large, so to promote the nitrification reaction, aeration is performed using the auxiliary aeration means 5b installed in the second zone Z2, and the second zone Z2 is used as an aerobic section (Figure 1 (lower diagram)).

First, the water level in the reaction tank 1 is set to the wastewater overflow position of the second partition plate 7b (a position higher than WL2 in Figure 1 (lower diagram)), and wastewater treatment is carried out in this state for 7.5 minutes.

Figure 4 is a side view that shows the schematic flow of wastewater when the water level in the reaction tank 1 in Figure 1 is at the wastewater overflow position (higher than WL2) of the second partition plate 7b and the wastewater is aerated by the auxiliary aeration device 5b in the second region.

When the water level in the reaction tank 1 is at the wastewater overflow position of the second partition plate 7b, the wastewater that has overflowed the upper end of the partition plate 7a from the first area Z1 and the wastewater that has risen in the second area Z2 due to aeration from the auxiliary aeration means 5b cross the upper end of 7b and move to the third area Z3 outside the partition plate 7b. The wastewater then descends in the third area Z3, passes through an area below the partition plate 7b, and returns to the first area Z1 inside the partition plate 7a and the second area Z2 inside the partition plate 7b. That is, a circulation flow that circulates between the first area Z1 and the third area Z3, and a circulation flow that circulates between the second area Z2 and the third area Z3 are formed (Figure 4). When the circulation flow is formed, a nitrification reaction that converts ammonia to nitrite and nitrate in the presence of oxygen proceeds in the first area Z1 (aerobic section) and the second area Z2 (aerobic section). Most of the air in the first zone Z1 and the second zone Z2 is released outside the reaction tank 1 without moving to the third zone Z3, and in the third zone Z3 (anoxic zone), a denitrification reaction takes place in which the nitrite and nitrate that have moved from the first zone Z1 and the second zone Z2 via the circulation flow are converted into nitrogen.

Next, the water level of the wastewater in the reaction tank 1 is set to the wastewater overflow position of the first partition plate 7a, that is, the position where the wastewater overflows the first partition plate 7a but does not overflow the second partition plate 7b (the position between WL1 and WL2 in FIG. 1 (lower diagram)), and wastewater treatment is performed in this state for 7.5 minutes. At this time, the flow of wastewater is interrupted between the first zone Z1 and the second zone Z2 and the third zone Z3, and a circulation flow via the third zone Z3 is not formed. Therefore, in the first zone Z1 (aerobic zone) and the second zone Z2 (aerobic zone), a nitrification reaction that converts ammonia to nitrite and nitrate in the presence of oxygen proceeds, and in the third zone Z3 (anoxic zone), a denitrification reaction that converts nitrite and nitrate that have moved from the first zone Z1 and the second zone Z2 to nitrogen proceeds before the flow of wastewater is interrupted.

The operation with the first partition plate 7b in the sewage overflow position (7.5 minutes) and the operation with the first partition plate 7a in the sewage overflow position (7.5 minutes) as described above constitute one interval (15 minutes), and the operation is performed by repeating the interval multiple times. This makes it possible to promote nitrification reactions in the first zone Z1 and the second zone Z2, while achieving good nitrogen removal in the third zone Z3, even during high-load periods.

During high-load periods, the amount of oxygen used in the nitrification reaction can be supplemented by aeration from the auxiliary aeration means 5a located in the first zone Z1 (Figure 4). By using both the auxiliary aeration means 5a located in the first zone Z1 and the auxiliary aeration means 5b located in the second zone Z2, the efficiency of oxygen dissolution in the wastewater can be improved, so the amount of air sent from the blower can be reduced compared to when the same amount of oxygen is supplied, achieving energy savings. Also, during high-load periods, wastewater treatment with increased membrane flux is required as the amount of treated water increases, but energy-saving operation can be achieved by keeping the amount of cleaning air from the aeration pipe 4 to a minimum.

(low load time period)
The following describes a method for treating wastewater during low-load periods when the amount of wastewater flowing into the reaction tank 1 is small and the inflow load is small.

During low load periods, the inflow of raw water containing organic matter and ammonia is small, so the third zone Z3 is not used as a reaction zone but as a raw water inlet conduit, the auxiliary aeration means 5b is stopped, and the second zone Z2 is used as an anoxic zone or anaerobic zone (Figure 1 (lower diagram)). Also, because the inflow is small, the rate at which the water level rises is slow, so the sewage overflow zone and sewage overflow stop zone are lengthened, and the interval time is set long.

First, the water level in the reaction tank 1 is set to the wastewater overflow position of the first partition plate 7a, that is, the position where the wastewater overflows the first partition plate 7a but does not overflow the second partition plate 7b (the position between WL1 and WL2 in FIG. 1 (lower drawing)), and wastewater treatment is performed in this state for 15 minutes (FIG. 2) (first overflow step). At this time, air is supplied from the air diffuser 4 to the membrane separation device 2, so that the wastewater overflows the upper end of the partition plate 7a from the first area Z1 and moves to the second area Z2 outside the partition plate 7a. The wastewater then descends in the second area Z2, passes through the area below the partition plate 7a, and returns to the first area Z1, which is the internal area of the partition plate 7a, forming a circulating flow that circulates around the partition plate 7a (FIG. 2). When the circulation flow is formed, a nitrification reaction takes place in the first zone Z1 (aerobic zone) in which ammonia is converted to nitrite and nitrate in the presence of oxygen, and a denitrification reaction takes place in the second zone Z2 (anoxic zone) in which the nitrite and nitrate that have been transported from the first zone Z1 by the circulation flow are converted to nitrogen.

Then, the wastewater level in the reaction tank 1 is set to the wastewater non-overflow position of the first partition plate 7a (a position lower than WL1 in Figure 1 (lower diagram)), and wastewater treatment is performed in this state for 15 minutes (non-overflow step). At this time, the flow of wastewater is interrupted between the first zone Z1 and the second zone Z2, and no circulation flow is formed around the partition plate 7a. Therefore, in the first zone Z1 (aerobic zone), a nitrification reaction that converts ammonia to nitrite and nitrate in the presence of oxygen proceeds, and in the second zone Z2 (anoxic zone), a denitrification reaction that converts the nitrite and nitrate that moved from the first zone Z1 before the flow of wastewater was interrupted to nitrogen proceeds.

The second zone Z2 can be changed to an anaerobic zone after the denitrification reaction has progressed as an anoxic zone. Specifically, in the first overflow step, the water level in the reaction tank 1 is lowered to reduce the amount of overflow water of the first partition plate 7a, thereby changing the second zone Z2 from an anoxic zone to an anaerobic zone. In the non-overflow step, the wastewater treatment time is lengthened to change the second zone Z2 from an anoxic zone to an anaerobic zone. In the second zone Z2 that has become an anaerobic zone, a process is carried out in which phosphorus-accumulating bacteria contained in the wastewater release phosphorus. At this time, the wastewater in which the amount of phosphorus dissolved has increased due to the metabolism of the phosphorus-accumulating bacteria in the second zone returns to the first zone Z1 inside the partition plate 7a through the zone below the first partition plate 7a. In the first zone Z1 (aerobic zone), the phosphorus-accumulating bacteria take in excess phosphorus more than the amount released in the second zone Z2 (anaerobic zone). Wastewater containing phosphorus-accumulating bacteria that have ingested excessive amounts of phosphorus can have the phosphorus removed by separating the sludge containing the phosphorus-accumulating bacteria using membrane separation device 2.

During low load times, the operation is performed multiple times, with one interval (30 minutes) consisting of the operation (15 minutes) with the first partition plate 7a in the wastewater overflow position as described above and the operation (15 minutes) with the first partition plate 7a in the wastewater non-overflow position. By lengthening the time of one interval, it is possible to ensure sufficient nitrification time and denitrification time according to the low inflow load, and perform good nitrogen removal. Furthermore, good phosphorus removal can be performed by lengthening the interval time and reducing the amount of overflow water. In addition, the auxiliary aeration device 5a installed in the first zone Z1 is controlled to provide the minimum necessary air volume, while keeping the membrane flux small and controlling the membrane cleaning aeration volume from the aeration tube 4 to the minimum necessary. By performing such operation, energy-saving operation can be achieved.

As described above, the daily treatment time slots are divided into normal load time slots, high load time slots, and low load time slots in advance based on the daily flow rate fluctuations of the wastewater supplied to the wastewater treatment device, and optimal wastewater treatment is performed in the first, second, and third regions of each time slot. This makes it possible to simultaneously remove nitrogen and phosphorus from the wastewater, and to perform stable wastewater treatment even with fluctuations in the wastewater flow rate, thereby achieving energy-saving operation.

The degree of progress of the nitrification reaction in the reaction tank 1, the status of nitrogen removal, and the status of phosphorus removal can be understood from the measured values of the oxidation-reduction potential (ORP) and the concentrations of various components in the first, second, and third regions.

In the first zone, the membrane permeate water becomes the final treated water, so it is possible to judge whether the target water quality has been obtained based on the dissolved oxygen (DO) concentration, oxidation-reduction potential (ORP), ammonia nitrogen (NH ₄ -N) concentration, and nitrate nitrogen (NO ₃ -N) concentration in the first zone. For example, when the NH ₄ -N concentration in the first zone is higher than the target value and the DO concentration is low, it is considered that the nitrification reaction is not proceeding sufficiently, so it is necessary to control the aeration amount of the auxiliary aeration means 5a provided in the first zone to be increased. On the other hand, when the NO ₃ -N concentration in the first zone is higher than the target value and the DO concentration is high, it is considered that the denitrification reaction is proceeding excessively, so it is necessary to control the aeration amount of the auxiliary aeration means 5a provided in the first zone to be reduced. In addition, in order to promote the nitrification reaction, it is preferable to set the ORP of the first zone Z1 to 100 to 200 mV or more. When the ORP is lower than this, it is necessary to control the aeration amount of the auxiliary aeration means 5a to be increased. Furthermore, it is possible to make a comprehensive judgment based on these indicators.

In the second zone, when the operation is performed with the denitrification reaction as the main purpose, if the concentration of NO ₃ -N is higher than the target value, it is necessary to control the aeration amount of the auxiliary aeration means 5a provided in the first zone to be reduced. In order to promote the denitrification reaction, it is preferable to set the ORP of the second zone Z2 to -100 to 0 mV. In order to perform more preferable control according to the load state, it is important to take into consideration the conditions of the first zone and the third zone, and the measured values of other items (DO, NH ₄ -N) in the second zone. It is preferable to prepare an arithmetic formula using the above measured values in advance and control the auxiliary aeration means 5a and/or the auxiliary aeration means 5b based on this arithmetic formula.

In the third zone, when the operation is performed with the main purpose of releasing phosphorus by phosphorus-accumulating bacteria, it is preferable to set the ORP at -200 to -100 mV. In the first zone, since an anaerobic compartment is formed, it is preferable to maintain a state in which NO ₃ -N is not detected and NH ₄ -N is not decreased.

As described above, the amount of aeration from the auxiliary aeration means provided in the first or second zone can be controlled based on the measured values or the calculated values obtained from the measured values selected from the dissolved oxygen (DO) concentration, oxidation-reduction potential (ORP), ammonia nitrogen (NH ₄ -N) concentration and nitrate nitrogen (NO ₃ -N) concentration in the first zone, the dissolved oxygen (DO) concentration, oxidation-reduction potential (ORP), ammonia nitrogen (NH 4 -N) concentration and nitrate nitrogen (NO ₃ -N) concentration in the second zone, and the oxidation-reduction potential (ORP) and ammonia concentration in the third zone, thereby realizing an optimal operation method according to the classification of the load time zone. In addition, the ratio of the overflow time zone and the overflow stop time zone can be controlled based on the measured values or the calculated values obtained from the measured values. Furthermore, in a treatment plant where the measured values are automatically measured, the appropriate operation control can be performed by setting the control method by an arithmetic formula or the like using various measurement data.

Next, we will explain a wastewater treatment device and a wastewater treatment method according to another embodiment of the present invention.

Figure 5 is a top view showing a schematic diagram of a wastewater treatment device according to a second embodiment of the present invention.

The wastewater treatment device in FIG. 5 is basically the same as the first embodiment (FIG. 1) in terms of its configuration and operation, but differs from the first embodiment (FIG. 1) in that multiple third regions Z3 surrounded by the second partition plate 7b and the tank wall of the reaction tank are formed at the four corners of the reaction tank 1. In the following, we will omit explanations of the overlapping configurations and operations and will explain the different configurations and operations.

In FIG. 5, the second zone Z2 in the reaction tank 1 is surrounded by the first partition plate 7a and the second partition plate 7b, as well as the four tank walls of the reaction tank 1. In addition, a third zone Z3 is disposed at each of the four corners of the reaction tank 1. Here, the four corners of the reaction tank 1 refer to the four joints where the four tank walls constituting the reaction tank 1 are joined to each other. That is, in this embodiment, the reaction tank 1 is divided into a first zone Z1 surrounded by the first partition plate 7a and where a membrane separation device is disposed, a second zone Z2 surrounded by the first partition plate, the second partition plate, and the inner wall of the reaction tank, and four third zones Z3 surrounded by the second partition plate and the inner wall of the reaction tank.

As shown in Figure 5, by arranging the third zones Z3 at the four corners of the reaction tank 1, when the water level in the reaction tank 1 is set to the wastewater overflow position of the second partition plate 7b (corresponding to a position higher than WL2 in Figure 1 (lower diagram)), the circulation flow circulating through the first zone Z1 and the third zone Z3 is a circulation flow along the diagonal direction connecting the center and the four corners of the reaction tank 1. Since all four third zones Z3 formed in the reaction tank 1 have the same positional relationship with the first zone Z1, an anoxic or anaerobic state can be formed equally in the four third zones Z3, which has the advantage that the anoxic or anaerobic state can be easily controlled. In addition, when remodeling an existing water treatment facility, it has the advantage that it is easy to apply if the reaction tank shape is close to a square.

Figure 6 is a top view showing a schematic diagram of a wastewater treatment device according to a third embodiment of the present invention.

The wastewater treatment device in FIG. 6 is basically the same as the first embodiment (FIG. 1) in terms of its configuration and operation, but differs from the first embodiment (FIG. 1) in that a first region Z1 in which the membrane separation device 2 is disposed is disposed near one inner wall of the reaction tank 1, a third region Z3 is disposed near the inner wall opposite the one inner wall, and a second region Z2 is disposed between the first and third regions. In the following, explanations of overlapping configurations and operations will be omitted, and only different configurations and operations will be explained.

In FIG. 6, the first region Z1 is surrounded by the first partition plate 7a as well as the three inner walls of the reaction tank 1, and is located near one of the inner walls of the reaction tank 1. The second region Z2 is surrounded by the first partition plate 7a and the second partition plate 7b as well as the two opposing inner walls of the reaction tank 1. That is, in this embodiment, the reaction tank 1 is surrounded by the first partition plate 7a and the three inner walls of the reaction tank 1, and is divided into the first region Z1 where the membrane separation device is located, the second region Z2 surrounded by the first partition plate 7a, the second partition plate 7b, and the two opposing inner walls of the reaction tank 1, and the third region Z3 surrounded by the second partition plate and the three inner walls of the reaction tank.

As shown in Figure 6, by arranging the first, second, and third regions as a single region inside the reaction tank 1, it becomes easier to arrange equipment such as a membrane separation device, and it also becomes easier to control the circulation flow rate. In addition, when remodeling an existing water treatment facility, this method has the advantage of being easily applicable when the reaction tank is shaped like a long, narrow rectangle.

Figure 7 is a top view showing a schematic diagram of a wastewater treatment device according to a fourth embodiment of the present invention.

The wastewater treatment device in FIG. 7 is basically the same as the third embodiment (FIG. 6) in terms of its configuration and operation, but differs from the third embodiment (FIG. 6) in that the third area Z3 is divided into four areas surrounded by the second partition plate 7b, and the four areas Z3 are arranged so as to be in contact with the first partition plate 7a. In the following, we will omit explanations of the overlapping configurations and operations and will explain the different configurations and operations.

7, there are four third zones Z3 in the reaction tank 1, and each zone Z3 is surrounded by a second partition plate 7b consisting of four rectangular plate-shaped members and arranged so as to contact the first partition plate 7a. The second zone Z2 is surrounded by a tank wall facing the tank wall located near the membrane separation device 2, two tank walls joined thereto, the first partition plate 7a, and the second partition plate 7b. Since the second partition plate 7b is spaced from the bottom of the reaction tank 1 and arranged so as to contact the partition plate 7a, it is desirable to fix the second partition plate 7b to the reaction tank 1 in a stable state using a plate material or steel material. That is, in this embodiment, the reaction tank 1 is divided into a first zone Z1 surrounded by the first partition plate 7a and the three inner walls of the reaction tank 1, in which the membrane separation device is disposed, a second zone Z2 surrounded by the first partition plate 7a, the second partition plate 7b, and the three inner walls of the reaction tank, and four third zones Z3 surrounded by the second partition plate 7b.

Depending on the difference in water level between the first and second regions, the first partition plate 7a may be subjected to a large water pressure. In this embodiment, by providing multiple third regions Z3 surrounded by second partition plates 7b inside the reaction tank 1 and arranging these multiple third regions Z3 so that they are in contact with the first partition plate 7a, the second partition plate 7b functions as a reinforcing material for the first partition plate 7a, resulting in an advantageously highly durable wastewater treatment device.

The present invention has been described above using the above-mentioned embodiment, but the present invention is not limited to the above-mentioned embodiment.

The present invention provides a wastewater treatment device and method that can simultaneously remove nitrogen and phosphorus from wastewater and perform stable wastewater treatment even when the wastewater flow rate fluctuates.

REFERENCE SIGNS LIST 1 Reaction tank 2 Membrane separation device 3 Suction pump 4 Aeration pipe 5a, 5b Auxiliary aeration means 6 Raw water pump 7a First partition plate 7b Second partition plate Z1 First zone Z2 Second zone Z3 Third zone

Claims (15)

A wastewater treatment device including a membrane separation device for separating contaminants contained in wastewater in a reaction tank for treating the wastewater, and an aeration pipe for supplying air bubbles to the membrane separation device,
The reaction vessel comprises:
A first partition plate that divides the inside of the reaction tank into an area where the membrane separation device is arranged and an area where the membrane separation device is not arranged and is arranged away from the bottom of the reaction tank;
A second partition plate having an upper end higher than an upper end of the first partition plate and spaced apart from the bottom of the reaction tank in an area where the membrane separation device is not disposed;
a first region in which the membrane separation device is disposed;
a second region existing between the first partition plate and the second partition plate;
a third region surrounded by the second partition plate and an inner wall of the reaction vessel;
having
When the water level of the wastewater in the reaction tank is higher than the upper end of the first partition plate, the wastewater flows from the first region over the upper end of the first partition plate and moves to the second region,
A sewage treatment device characterized in that when the water level of the sewage in the reaction tank is higher than the upper end of the second partition plate, the sewage flows from the second area over the upper end of the second partition plate and moves to the third area . The wastewater treatment device according to claim 1, characterized in that when the wastewater level in the reaction tank is at a position higher than the upper end of the second partition plate, the wastewater forms a circulating flow that circulates between the first area and the third area . 3. The wastewater treatment device according to claim 1 , wherein the second area is surrounded by the first partition plate, the second partition plate and an inner wall of a reaction tank . 4. The wastewater treatment device according to claim 1, further comprising a wastewater supplying means for supplying wastewater to the third area. A wastewater treatment device including a membrane separation device for separating contaminants contained in wastewater in a reaction tank for treating the wastewater, and an aeration pipe for supplying air bubbles to the membrane separation device,
The reaction vessel comprises:
A first partition plate that divides the inside of the reaction tank into an area where the membrane separation device is arranged and an area where the membrane separation device is not arranged and is arranged away from the bottom of the reaction tank;
A second partition plate having an upper end higher than an upper end of the first partition plate and spaced apart from the bottom of the reaction tank in an area where the membrane separation device is not disposed;
a first region in which the membrane separation device is disposed;
a second region existing between the first partition plate and the second partition plate;
a third region surrounded by the second partition plate and an inner wall of the reaction vessel;
having
A wastewater treatment apparatus comprising : an auxiliary aeration means provided in the second area. 5. The wastewater treatment device according to claim 1, wherein a volume ratio of the first region to the second region to the third region is 1:1-2:0.2-1. 7. The wastewater treatment device according to claim 1, wherein at least one of the first partition plate and the second partition plate is provided with a water level adjustment means at an upper end thereof. A method for treating wastewater using the wastewater treatment device, comprising: a reaction tank for treating wastewater, a membrane separation device for separating pollutants contained in the wastewater, and an aeration pipe for supplying air bubbles to the membrane separation device, the reaction tank having a first partition plate that divides the inside of the reaction tank into an area where the membrane separation device is located and an area where the membrane separation device is not located, and that is disposed away from the bottom of the reaction tank, a second partition plate in the area where the membrane separation device is not located, that has an upper end higher than an upper end of the first partition plate and is disposed away from the bottom of the reaction tank , a first area where the membrane separation device is located, a second area present between the first partition plate and the second partition plate, and a third area surrounded by the second partition plate and an inner wall of the reaction tank,
A first overflow step in which, when the water level of the wastewater in the reaction tank is at a position higher than the upper end of the first partition plate, the wastewater flows from the first region over the upper end of the first partition plate and moves to the second region ;
A non-overflow step in which the wastewater does not overflow the first partition when the water level of the wastewater in the reaction tank is at a position lower than the upper end of the first partition ;
A second overflow step in which, when the water level of the wastewater in the reaction tank is at a position higher than the upper end of the second partition plate, the wastewater flows from the second region over the upper end of the second partition plate and moves to the third region ;
A wastewater treatment method comprising the steps of: A wastewater treatment method as described in claim 8, characterized in that when the wastewater level in the reaction tank is at a position higher than the upper end of the second partition plate, the wastewater forms a circulating flow that circulates between the first area and the third area . 10. The wastewater treatment method according to claim 8, wherein the second area is surrounded by the first partition plate, the second partition plate and an inner wall of the reaction tank . The wastewater treatment method according to any one of claims 8 to 10, characterized in that high-load time periods and/or low-load time periods are preset based on daily fluctuations in the flow rate of wastewater supplied to the wastewater treatment device. A method for treating wastewater using the wastewater treatment device, comprising: a reaction tank for treating wastewater, a membrane separation device for separating pollutants contained in the wastewater, and an aeration pipe for supplying air bubbles to the membrane separation device, the reaction tank having a first partition plate that divides the inside of the reaction tank into an area where the membrane separation device is located and an area where the membrane separation device is not located, and that is disposed away from the bottom of the reaction tank, a second partition plate in the area where the membrane separation device is not located, that has an upper end higher than an upper end of the first partition plate and is disposed away from the bottom of the reaction tank, a first area where the membrane separation device is located, a second area present between the first partition plate and the second partition plate, and a third area surrounded by the second partition plate and an inner wall of the reaction tank,
a first overflow step in which the wastewater overflows the first partition;
A non-overflow step in which the wastewater does not exceed the first partition plate;
a second overflow step in which the wastewater overflows the second partition;
having
A wastewater treatment method characterized in that high-load time periods and/or low-load time periods are set in advance based on daily flow rate fluctuations of wastewater supplied to the wastewater treatment device, and during the high-load time periods, a second area surrounded by the first partition plate and the second partition plate, or a second area surrounded by the first partition plate, the second partition plate and an inner wall of a reaction tank, is set as an aerobic compartment. The wastewater treatment method according to claim 11, characterized in that during the low load period, the second area surrounded by the first partition plate and the second partition plate, or the second area surrounded by the first partition plate, the second partition plate and the inner wall of the reaction tank, is an anoxic compartment or an anaerobic compartment. The wastewater treatment method according to claim 11 or 13, characterized in that the high-load time period and/ or the low-load time period are set based on measured values selected from wastewater inflow volume and wastewater quality or calculated values obtained from the measured values. A wastewater treatment method according to any one of claims 8 to 11, _{13 and 14} , characterized in that the aeration amount from an auxiliary aeration means provided in the first area or the second area is controlled based on measured values or calculated values obtained from the measured values selected from the dissolved oxygen (DO) concentration, oxidation-reduction potential (ORP), ammoniacal nitrogen (NH ₄ -N) concentration and nitrate nitrogen (NO ₃ -N) concentration in the first area, the dissolved oxygen (DO) concentration, oxidation-reduction potential (ORP), ammoniacal nitrogen (NH 4 -N) concentration and nitrate nitrogen (NO 3 -N ) concentration in the second area, and the oxidation-reduction potential (ORP) and ammonia concentration in the third area.

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