Sewage treatment apparatus and sewage treatment method

Abstract

The present invention provides a wastewater treatment device and a wastewater treatment method in which a nitrification and denitrification reaction are performed efficiently in accurate correspondence with daily wastewater load variations, and which are energy saving with reduced power consumption.　The wastewater treatment device comprises a membrane separation device 2, a diffuser tube 4, and a partition plate 7 which are in a reaction vessel 1, and also comprises: a means for pre-setting a target value of at least one control item selected from among interval time, overflow time ratio, overflow water depth, the operation method of a raw water pump 6, and the operation method of a suction pump 3, in accordance with wastewater load variations; a means for detecting the load variations of the wastewater supplied to the wastewater treatment device; and a means for controlling, on the basis of the detected load variations, the control item attains the preset target value.

Description

Technical Field

[0001] The present invention relates to a sewage treatment apparatus and a sewage treatment method.

Background Art

[0002] Conventionally, there is known a sewage treatment apparatus including a reaction tank for biologically treating sewage, a membrane separation device immersed in the reaction tank and removing solids from the biologically treated sewage, and a diffuser pipe installed below the membrane separation device and supplying a gas such as air to the membrane separation device. The biological treatment of sewage in the reaction tank is carried out based on the activated sludge method in which sewage is treated by so-called activated sludge.

[0003] In the activated sludge method, a nitrification reaction that converts ammonia to nitrous acid or nitric acid in the presence of oxygen (aerobic state) is carried out, and a denitrification reaction that converts nitrous acid or nitric acid to nitrogen in an oxygen-free state is carried out. In recent years, in order to achieve space saving of sewage treatment apparatuses, a partition plate insertion type sewage treatment apparatus in which a nitrification reaction and a denitrification reaction are carried out in a single reaction tank has been proposed (see, for example, Patent Documents 1 and 2).

[0004] FIG. 8 is a diagram schematically showing a conventional sewage treatment apparatus. The sewage treatment apparatus of FIG. 8 includes a reaction tank 1 that performs a nitrification reaction in an aerobic state and a denitrification reaction in an oxygen-free state, and a raw water tank 9 for supplying sewage to the reaction tank 1. The reaction tank 1 has a partition plate 7 for partitioning the inside of the reaction tank 1 into a plurality of compartments. The reaction tank 1 is partitioned into a sewage region A surrounded by the partition plate 7 and a sewage region B surrounded by the partition plate 7 and the inner wall of the reaction tank 1. The sewage region A has a membrane separation device 2 and a diffuser pipe 4.

[0005] In the sewage treatment apparatus of FIG. 8, when the water level in the reaction tank 1 reaches the sewage supply start water level LWL, the supply of sewage from the raw water tank 9 is started, and when the water level reaches the sewage supply stop water level HWL, the supply of sewage from the raw water tank 9 is stopped, and it is configured such that the water level of the sewage changes. As a result, the water level of the sewage alternates 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 schematically showing the flow of sewage when the water level of the sewage in the reaction tank 1 in FIG. 8 is at the sewage overflow position.

[0006] When the water level of the sewage is at the sewage overflow position, due to the air supplied from the air diffuser pipe 4 to the membrane separation device 2, the sewage overflows the upper end of the partition plate 7, and a circulating flow is formed that circulates around the partition plate 7. Due to this circulating flow, nitrous acid and nitric acid in the sewage region A migrate to the sewage region B, and most of the air in the sewage region A is discharged outside the reaction tank 1 without migrating to the sewage region B. That is, when the circulating flow is formed, a nitrification reaction that converts ammonia to nitrous acid and nitric acid in the presence of oxygen proceeds in the sewage region A, and a denitrification reaction that converts nitrous acid and nitric acid that have migrated from the sewage region along the circulating flow to nitrogen proceeds in the sewage region B.

[0007] On the other hand, when the water level of the sewage is at the sewage non-overflow position, since the flow of the sewage between the sewage region A and the sewage region B is interrupted, even if the air diffuser pipe 4 supplies air to the membrane separation device 2, a circulating flow that circulates around the partition plate 7 is not formed. That is, a nitrification reaction that converts ammonia to nitrous acid and nitric acid in the presence of oxygen proceeds in the sewage region A, and a denitrification reaction that converts nitrous acid and nitric acid that have migrated from the sewage region A before the flow of the sewage is interrupted to nitrogen proceeds in the sewage region B.

[0008] In such a partition plate insertion type sewage treatment device, there are an internal area A and an external area B of the partition plate. Sewage treatment is carried out by repeating a time zone (overflow time zone) in which the water level in the reaction tank exceeds the partition plate and a circulation flow is formed, and a time zone (overflow stop time zone) in which the water level in the reaction tank becomes lower than the partition plate and the circulation stops. Therefore, different control is required compared to a general sewage treatment device without a partition plate, in which the inside of the reaction tank is always in a state close to complete mixing.

[0009] In addition, the daily variation in the inflow sewage volume at a sewage treatment plant is predicted to vary by about 0 to 3 times the daily average sewage volume. Even when a flow adjustment tank or the like is provided for control, it is difficult to make the inflow sewage volume into the reaction tank uniform. For example, in a small-scale treatment device, the operation of the reaction tank corresponding to a variation of about 2 times the daily average sewage volume, and in a medium- to large-scale treatment device, the operation of the reaction tank corresponding to a variation of about 1.6 times the daily average sewage volume is required.

[0010] Regarding the partition plate insertion type sewage treatment device, as a sewage treatment method according to the daily variation in the inflow sewage volume, a method has been reported in which a dissolved oxygen meter and auxiliary aeration means are provided in the aerobic section, and the aeration amount by the auxiliary aeration means is controlled so that the dissolved oxygen concentration measured by the dissolved oxygen meter becomes a preset target value (Patent Document 2).

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] In the method of Patent Document 2, the aeration amount by the auxiliary aeration means is controlled so that the dissolved oxygen concentration in the aerobic compartment becomes a target value preset according to the load situation of the influent raw water. However, the reaction behavior in the reaction tank where the overflow time zone and the overflow stop time zone are repeated is not sufficiently reflected, and there has been a demand for a control method that can accurately respond to the daily load fluctuations of the raw water.

[0013] In addition, in a sewage treatment apparatus having a membrane separation device, it has been necessary to constantly perform aeration cleaning of the membrane surface to prevent clogging of the membrane surface, and a large amount of power has been consumed. In recent years, however, reduction of the aeration amount for membrane cleaning for the purpose of energy saving has been achieved. On the other hand, an auxiliary aeration means for supplying oxygen necessary for the biological reaction is provided in the sewage treatment apparatus, but reducing the auxiliary aeration air volume has been an important issue in order to further suppress power consumption and achieve energy saving.

[0014] An object of the present invention is to provide an energy-saving sewage treatment apparatus and a sewage treatment method that accurately respond to daily load fluctuations of sewage, efficiently perform nitrification and denitrification reactions, and suppress power consumption in sewage treatment using a partition plate insertion type sewage treatment apparatus.

Means for Solving the Problems

[0015] In order to achieve the above object, the sewage treatment apparatus of the present invention includes a membrane separation device for separating contaminants contained in the sewage inside a reaction tank for treating sewage, a diffuser pipe for supplying bubbles to the membrane separation device, and a partition plate for partitioning the region where the membrane separation device is disposed and other regions. Huh Means for presetting a target value of at least one control item selected from an interval time, an overflow time ratio, an overflow water depth, an operation method of a raw water pump, and an operation method of a suction pump according to load fluctuations of sewage supplied to the sewage treatment apparatus, means for detecting load fluctuations of sewage supplied to the sewage treatment apparatus, and means for controlling the at least one control item to a preset target value based on the detected load fluctuations. In a sewage treatment apparatus, means for detecting a change pattern of the amount of dissolved oxygen in the region where the membrane separation device is disposed in a first interval, means for setting a target value of the auxiliary aeration air volume in a second interval based on the detected change pattern, and means for controlling the auxiliary aeration air volume to be the target value in the second interval It is characterized by the above. To achieve the above object, the sewage treatment apparatus of the present invention includes a membrane separation device for separating contaminants contained in the sewage inside a reaction tank for treating sewage, a diffuser pipe for supplying bubbles to the membrane separation device, and a partition plate for partitioning the region where the membrane separation device is disposed and other regions. In response to a load fluctuation of the sewage supplied to the sewage treatment apparatus, means for presetting a target value of at least one control item selected from an interval time, an overflow time ratio, an overflow water depth, an operation method of a raw material pump, and an operation method of a suction pump, means for detecting a load fluctuation of the sewage supplied to the sewage treatment apparatus, and means for controlling the at least one control item to be a preset target value based on the detected load fluctuation. In the sewage treatment apparatus, means for detecting the concentration of ammoniacal nitrogen (NH 4 -N) and / or nitrate nitrogen (NO 3-N) in the region where the membrane separation device is disposed at the start time of overflow in a first interval, means for setting a target value of the overflow stop time in a second interval based on the detected concentration, and means for controlling the overflow stop time to be the target value in the second interval

[0016] In order to achieve the above object, the sewage treatment apparatus of the present invention is a sewage treatment apparatus including a membrane separation device for separating contaminants contained in the sewage inside a reaction tank for treating sewage, an air diffuser for supplying bubbles to the membrane separation device, and a partition plate for partitioning the region where the membrane separation device is disposed and other regions. The sewage treatment apparatus is characterized by comprising means for detecting a change pattern of the dissolved oxygen amount in the region where the membrane separation device is disposed in a first interval, means for setting a target value of the auxiliary aeration air volume from the auxiliary aeration means in a second interval based on the detected change pattern, and means for controlling the auxiliary aeration air volume to be the target value in the second interval.

[0017] In order to achieve the above object, the sewage treatment apparatus of the present invention is a sewage treatment apparatus including a membrane separation device for separating contaminants contained in the sewage inside a reaction tank for treating sewage, an air diffuser for supplying bubbles to the membrane separation device, and a partition plate for partitioning the region where the membrane separation device is disposed and other regions. The sewage treatment apparatus is characterized by comprising means for detecting the ammonia nitrogen (NH4-N) concentration and / or the nitrate nitrogen (NO3-N) concentration in the region where the membrane separation device is disposed at the start point of overflow in a first interval, means for setting a target value of the overflow stop time in a second interval based on the detected concentration, and means for controlling the overflow stop time to be the target value in the second interval.

[0018] In order to achieve the above object, the sewage treatment method of the present invention is a sewage treatment method using the sewage treatment apparatus of the present invention, and according to the load fluctuation of the sewage supplied to the sewage treatment apparatus, an interval time, an overflow time ratio, an overflow water depth, a driving method of the raw water pump, and at least one control item selected from the driving method of the suction pump are set in advance. A step of setting a target value, a step of detecting a load fluctuation of the sewage supplied to the sewage treatment apparatus, and a step of controlling at least one of the control items to be a preset target value based on the detected load fluctuation. It is characterized by having.

[0019] In order to achieve the above object, the sewage treatment method of the present invention is a sewage treatment method using the sewage treatment apparatus of the present invention, and in the first interval, a step of detecting a change pattern of the dissolved oxygen amount in the region where the membrane separation apparatus is arranged, and based on the detected change pattern, a step of setting a target value of the auxiliary aeration air volume from the auxiliary aeration means in the second interval, and in the second interval, a step of controlling the auxiliary aeration air volume to be the target value. It is characterized by having.

[0020] In order to achieve the above object, the sewage treatment method of the present invention is a sewage treatment method using the sewage treatment apparatus of the present invention, and at the start time of overflow in the first interval, a step of detecting the ammonia nitrogen (NH4-N) concentration and / or the nitrate nitrogen (NO3-N) concentration in the region where the membrane separation apparatus is arranged, and based on the detected concentration, a step of setting a target value of the overflow stop time in the second interval, and in the second interval, a step of controlling the overflow stop time to be the target value. It is characterized by having.

Effect of the Invention

[0021] According to the present invention, it is possible to accurately respond to the daily load fluctuation of sewage, efficiently execute the nitrification reaction and the denitrification reaction, and perform energy-saving sewage treatment with suppressed power consumption.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing a sewage treatment apparatus according to an embodiment of the present invention.

[0024] The sewage treatment apparatus 10 shown in Fig. 1 includes a raw water tank 9 for storing sewage, a single-tank reaction tank 1 for biologically treating sewage, and a flow adjustment tank 8 for adjusting the flow rate of sewage supplied from the raw water tank 9 to the reaction tank 1. The reaction tank 1 has a membrane separation device 2 for separating contaminants contained in the sewage, an air diffuser pipe 4 for supplying bubble-shaped air to the membrane separation device 2, and a partition plate 7 for partitioning the inside of the reaction tank 1 into a region where the membrane separation device 2 is disposed and other regions. The bottom of the partition plate 7 is provided at a distance from the bottom surface of the reaction tank 1. The partition plate 7 surrounds the entire lateral periphery of the membrane separation device 2, partitioning the inside of the reaction tank 1 into an internal region 11 (aerobic compartment) where the membrane separation device 2 and the air diffuser pipe 4 are disposed and an external region 12 outside the internal region 11. The partition plate 7 may surround the membrane separation device 2 in combination with the tank wall of the reaction tank 1. 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 sewage is filtered by the membrane separation device 2, and the filtered water is taken out of the reaction tank 1.

[0025] The air diffuser pipe 4 (membrane cleaning aeration means) is installed below the membrane separation device 2 and is connected to a blower B1 outside the reaction tank 1, and the blower B1 supplies air to the air diffuser pipe 4. Since the membrane separation device 2 filters sewage, sludge substances and the like in the sewage adhere to the membrane surface of the membrane separation device 2. If the sludge substances and the like in the sewage adhering to the membrane surface of the membrane separation device 2 are left unattended, the membrane separation device 2 will become clogged and will not be able to properly filter the sewage. Therefore, by supplying the air supplied from the blower B1 to the air diffuser pipe 4 to the membrane surface of the membrane separation device 2, it is possible to prevent sludge substances and the like from adhering to the membrane surface of the membrane separation device 2.

[0026] Auxiliary aeration means 5 is provided on the side of the lower part of the membrane separation device 2 to supply oxygen that is insufficient in the oxygen supply by the air diffuser pipe 4 (membrane cleaning aeration means). The auxiliary aeration means 5 is connected to a blower B2 outside the reaction tank 1, and the blower B2 supplies air to the auxiliary aeration means 5. As the auxiliary aeration means 5, a membrane-type air diffuser device that usually generates fine bubbles is generally used, and generally, the oxygen transfer efficiency is 2 to 5 times higher than that of the air diffuser pipe 4 (cleaning aeration means).

[0027] The sewage stored in the original water tank 9 is transferred to the flow rate adjustment tank 8. After the flow rate of the sewage is adjusted in the flow rate adjustment tank 8, it is supplied to the reaction tank 1 by the raw water pump 6. The sewage with adjusted flow rate is supplied to the external area 12 surrounded by the partition plate 7 in the reaction tank 1 and the tank wall of the reaction tank 1 by the sewage supply means.

[0028] The reaction tank 1 contains organic sludge containing microorganisms, that is, so-called activated sludge, and these microorganisms decompose organic substances to perform biological treatment. These microorganisms include nitrifying bacteria for performing nitrification reaction in the internal area 11 and denitrifying bacteria for performing denitrification reaction in the external area 12 in order to execute the treatment of sewage. The sludge itself containing these microorganisms is well-known in this field.

[0029] For the membrane separation device 2, a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, etc. can be used, and the shape of the membrane can be a flat membrane, a hollow fiber membrane, etc. The membrane separation device itself used in the present invention is well-known in this field.

[0030] FIG. 2 is a diagram schematically showing the flow of sewage when the water level in the reaction tank in FIG. 1 is at the sewage overflow position of the partition plate 7.

[0031] When the water level in the reaction tank 1 is at the sewage overflow position of the partition plate 7, air is supplied from the air diffuser 4 to the membrane separation device 2, so that the sewage overflows from the internal area 11 over the upper end of the partition plate 7 and moves to the external area 12 of the partition plate 7. Then, the sewage descends in the external area 12, passes through the area below the partition plate 7, and returns to the internal area 11 of the partition plate 7. That is, when the water level of the sewage is at the sewage overflow position of the partition plate 7 and the sewage overflows the partition plate 7, a circulating flow is formed around the partition plate 7. When the circulating flow is formed, for example, nitrous acid and nitric acid in the internal area 11 migrate to the external area, and most of the air in the internal area 11 is discharged to the outside of the reaction tank 1 without migrating to the external area 12. At this time, in the internal area 11 (aerobic compartment), a nitrification reaction that converts ammonia to nitrous acid or nitric acid proceeds in the presence of oxygen, and in the external area 12 (anaerobic compartment), a denitrification reaction that converts nitrous acid and nitric acid that have moved from the internal area along the circulating flow to nitrogen proceeds.

[0032] On the one hand, when the water level of the sewage is at the sewage non-overflow position and the flow of sewage is interrupted between the internal region 11 and the external region 12, even if the air diffuser pipe 4 supplies air to the membrane separation device 2, a circulating flow that circulates around the partition plate 7 is not formed. Therefore, in the internal region 11 (aerobic compartment), a nitrification reaction that converts ammonia to nitrite or nitrate proceeds in the presence of oxygen, and in the external region 12, a denitrification reaction that converts nitrite or nitrate that has moved from the internal region 11 before the flow of sewage is interrupted to nitrogen proceeds.

[0033] In the present invention, the aerobic state refers to a state in which oxygen molecules are dissolved in the sewage, and the anoxic state refers to a state in which oxygen molecules are not dissolved in the sewage but bound oxygen is dissolved in the form of nitrate or nitrite.

[0034] The change in the water level of the sewage in the reaction tank 1 is generally carried out by changing the supply amount of the raw water supplied into the reaction tank 1 by the raw water pump 6 from the flow rate adjustment tank 8, but the suction amount of the membrane may also be changed. Furthermore, the sewage treatment device may have a water level control means for adjusting the water level in the reaction tank 1. As the water level control means, for example, there is a liquid level sensor that examines the water level in the reaction tank 1, that is, the position of the liquid surface. When the liquid level sensor detects the water level of the sewage, the raw water pump 6 automatically controls the amount of raw water supplied to the reaction tank 1 by the sewage supply means.

[0035] In this way, in the present embodiment, since sewage treatment is performed by repeating the overflow time zone in which the water level of the reaction tank exceeds the partition plate and a circulating flow is formed and the overflow stop time zone in which the water level of the reaction tank becomes lower than the partition plate and the circulation stops, it is necessary to perform control that sufficiently reflects the reaction behavior in both time zones. Hereinafter, a unit obtained by combining one overflow time zone and one overflow stop time zone that are consecutive to each other is referred to as an interval.

[0036] (First Embodiment) Hereinafter, the first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 3 is a flowchart showing the procedure of sewage treatment executed according to the first embodiment.

[0037] In this embodiment, in response to fluctuations in the load of the supplied sewage, in addition to the target values of the membrane flux and the aeration air volume for membrane cleaning, the target value of at least one control item selected from the interval time, the overflow time ratio, the overflow water depth, the operation method of the raw water pump, and the operation method of the suction pump is preset (S101).

[0038] Examples of fluctuations in the load of sewage include changes in the inflow sewage volume and the concentration of pollutants. Specifically, examples include fluctuations in the flow rate of the raw water pump 1, the water level of the raw water tank 9, the water level of the flow adjustment tank 8, the COD (chemical oxygen demand) concentration of the raw water, the T-N (total nitrogen) concentration, and the T-P (total phosphorus) concentration. These load fluctuations can be measured by a raw water pump flow meter (installed at 6 in FIG. 1), a raw water tank water level meter (installed at 9 in FIG. 1), a flow adjustment tank water level meter (installed at 8 in FIG. 1), a raw water COD concentration meter, a T-N concentration meter, and a T-P concentration meter (raw water component concentration meter C1 in FIG. 1), respectively.

[0039] For example, when the daily average load fluctuation of sewage is Q, the load fluctuations can be classified into multiple stages such as 0 to 0.4Q, 0.4Q to 0.8Q, 0.8Q to 1.2Q, 1.2Q to 1.6Q, and 1.6Q to 2Q. For the load fluctuations in each category, the target value of at least one of the above control items is preset (S101).

[0040] Table 1 below shows an example of the target value of each control item set according to the classification of load fluctuations. The membrane flux represents the amount of membrane filtration water per unit membrane area and per unit time (m 3 / m 2 / d), and the aeration air volume for membrane cleaning (SADm) represents the aeration air volume from the diffuser pipe 4 (Nm 3 / m 2 / h). The target value of the aeration air volume for membrane cleaning can be set corresponding to the target value of the membrane flux. As shown in Table 1, the target values of the membrane flux and the aeration air volume for membrane cleaning are set to increase as the load (inflow water volume) of the sewage increases from a low load to a high load.

[0041]

Table 1

[0042] The following describes the setting of the target values of the control items characteristic of the partition plate insertion type sewage treatment apparatus.

[0043] (Interval time) The interval time refers to the time required for one interval, which is the sum of one overflow time zone and one overflow stop time zone that are consecutive to each other. In the present embodiment, for example, as shown in Table 1 above, the target value of the interval time is set according to the load fluctuation of the sewage, and the interval time is set to be shorter as the load of the sewage changes from a low load to a high load.

[0044] In the low load time zone, since the inflow amount of the raw water containing organic substances and ammonia is small and the rising speed of the water level is slow, the overflow time zone and the overflow stop time zone are lengthened to set a long interval time. On the other hand, in the high load time zone, since the inflow amount of the raw water is large and the rising speed of the water level is fast, the overflow time zone and the overflow stop time zone are shortened to set a short interval time. The target value of the interval time according to the load fluctuation of the sewage is set with reference to other control items, taking as a reference the value obtained by multiplying the reciprocal of the square root of the flow rate ratio by 15 minutes in the normal load time zone (0.8Q to 1.2Q).

[0045] (Overflow time ratio) The overflow time ratio refers to the ratio (%) of the overflow time in one interval. In the present embodiment, for example, as shown in Table 1 above, the target value of the overflow time ratio is set according to the load fluctuation of the sewage, and the overflow time ratio is set to increase as the load of the sewage changes from a low load to a high load.

[0046] In the high load time zone, since the inflow amount of the raw water containing organic substances and ammonia is large, it is necessary to maintain a high reaction rate of the oxidation reaction of organic substances (such as BOD) and then the oxidation reaction of ammonia and ensure the necessary reaction time. For this reason, the overflow time ratio is increased to control so as to maintain the entire reaction layer 1 in an aerobic state. The target value of the overflow time ratio according to the sewage load variation is determined in consideration of the ratio of the nitrification rate to the denitrification rate. Generally, in the high-load time zone, the nitrification rate decreases and the denitrification rate increases. Also, in the low-load time zone, the nitrification rate increases and the denitrification rate decreases. The overflow time ratio in the normal load time zone is about 40%, and it is set in the range of about 20 - 60% according to the degree of the load. Note that, instead of the overflow time ratio, the target value may be set and controlled with the overflow stop time ratio (%) as the control item.

[0047] (Overflow water depth) The overflow water depth refers to the difference between the water level in the reaction tank 1 and the upper end of the partition plate 7. In this embodiment, for example, as shown in Table 1 above, the target value of the overflow water depth is set according to the sewage load variation, and the overflow water depth is set to become deeper as the sewage load changes from low load to high load. The overflow water depth affects the circulating water volume (the flow rate of the circulating flow formed in the overflow time zone) together with the aeration air volume for membrane cleaning and the auxiliary aeration air volume. The deeper the overflow water depth, the larger the circulating water volume. The value obtained by dividing the circulating water volume by the raw water volume is called the circulation rate, which affects the nitrogen removal rate. The higher the circulation rate, the higher the nitrogen removal rate, but if it is made too large, it will lead to an increase in energy consumption. There is an optimal value considering the nitrogen removal rate and energy consumption, which is usually about 3 - 10 times.

[0048] In the low-load time zone, since the nitrogen concentration of the raw water is also low and a high nitrogen removal rate is not required, the overflow water depth is set to be small so as to result in a low circulation rate. On the other hand, in the high-load time zone, since the nitrogen concentration of the raw water is also high and a high nitrogen removal rate is required, the overflow water depth is set to be deep so as to result in a high circulation rate. The target value of the overflow water depth according to the sewage load variation is set by setting an optimal circulation rate and considering the length of the upper end portion of the partition plate, the aeration air volume for membrane cleaning, and the auxiliary aeration air volume. In this embodiment, it is set in the range of 1 - 50 cm according to the load variation.

[0049] (Operation method of the raw water pump: Supply time of the raw water) The sewage supplied to the reaction tank 1 can be controlled by changing the operation method of the raw water pump 6. Examples of the operation method of the raw water pump 6 include the supply time of the raw water. In the present embodiment, as shown in Table 1 above, the target value of the supply time of the raw water is set according to the load fluctuation of the sewage. Specifically, as the load of the sewage increases from a low load to a high load, the supply of the raw water is set to be from the supply centered on the overflow stop time zone to the supply in both the overflow stop time zone and the overflow time zone.

[0050] In a low load time zone with a small inflow water volume, in order to supply an electron donor necessary for the denitrification reaction and perform efficient nitrification and denitrification, it is preferable to supply the raw water to the outer region 12 of the partition plate in the overflow stop time zone. In the low load time zone and the normal load time zone, as the load of the sewage increases, the supply time of the raw water in the overflow stop time zone can be set to be longer.

[0051] In a high load time zone with a large inflow water volume, if the raw water is supplied only in the overflow stop time zone, the discharge flow rate will increase, so a large raw water pump is required. In addition, it is difficult to control because of a rapid rise in the water level of the reaction tank and a rapid increase in the load. Therefore, in the high load time zone, it is necessary to set the supply time of the raw water to be longer so that it becomes a part of the overflow stop time zone and the overflow time zone, and even all (continuous) of the overflow stop time zone and the overflow time zone, in order to suppress a rapid change in the reaction tank. The target value of the operation method (supply time of the raw water) of the raw water pump 6 according to the load fluctuation of the sewage is, in principle, supplied in the overflow stop time zone + a part of the overflow time zone (time required for the water level to rise). However, when the raw water supply amount exceeds the set value, the supply time is set to be longer including the overflow time zone.

[0052] (Operation method of the suction pump) The water filtered by the membrane separation device 2 can be controlled by changing the operation method of the suction pump 3. The operation methods of the suction pump 3 include the suction volume, operation time, and stop time. Considering the raw water supply volume, overflow water depth, and interval (overflow stop time zone and overflow time zone), the suction volume is controlled so that the water level in the reaction tank can be appropriately controlled.

[0053] The suction pump 3 performs intermittent operation (9-minute operation - 1-minute stop) regardless of the load fluctuation of the sewage in order to prevent clogging of the membrane surface of the membrane separation device 2. In this embodiment, as shown in Table 1 above, target values for the operation time and stop time are set according to the load fluctuation of the sewage. Specifically, as the load of the sewage increases from a low load to a high load, the target value is set so that the operation time increases. During the low load time zone, the suction volume is reduced, and the operation time is set to be shorter and the stop time to be longer at an interval of 10 minutes (for example, 5-minute operation - 5-minute stop). On the other hand, during the high load time zone, the suction volume is increased, and the operation time is set to be longer and the stop time to be shorter (for example, 14.5-minute operation - 0.5-minute stop).

[0054] After setting the target values for each control item according to the load fluctuation of the sewage as described above, the load fluctuation of the sewage supplied to the reaction tank 1 in actual sewage treatment is detected (S102). Examples of the load fluctuation of the sewage include changes in the inflow sewage volume and the concentration of pollutants as in the case of setting the above target values. Specifically, it includes at least one fluctuation selected from the flow rate of the raw water pump 1, the water level of the raw water tank 9, the water level of the flow adjustment tank 8, the COD concentration, T-N concentration, and T-P concentration of the raw water. The load fluctuation of the sewage can be measured by at least one means selected from a raw water pump flow meter (installed at 6 in FIG. 1), a raw water tank water level meter (installed at 9 in FIG. 1), a flow adjustment tank water level meter (installed at 8 in FIG. 1), a raw water COD concentration meter, a T-N concentration meter, and a T-P concentration meter (raw water component concentration meter C1 in FIG. 1). Several types of means can be combined and used. The load fluctuation of the sewage is measured for a time corresponding to one interval using the above means, and the average value can be used as the detected value.

[0055] The detected load fluctuation of the sewage is classified into any one of the above-mentioned classifications of 0 to 0.4Q, 0.4Q to 0.8Q, 0.8Q to 1.2Q, 1.2Q to 1.6Q, and 1.6Q to 2Q, with the daily average load fluctuation being Q, and the target values of each control item are set. The target values of each control item set in the load fluctuation of the corresponding classification are specified (S103).

[0056] Next, while performing sewage treatment, it is controlled so that each of the above control items becomes the specified target value (S104). In order to control the membrane flux and the operation method of the suction pump to the target value, it is executed by adjusting the suction flow rate by the suction pump 3. In order to control the aeration air volume for membrane cleaning to the target value, it is executed by adjusting the air flow rate supplied from the blower B1 for membrane cleaning to the air diffuser pipe 4 (aeration means for membrane cleaning). In order to control the interval time, the overflow time ratio, and the overflow water depth to the target value, it is executed by adjusting the supply flow rate and supply time from the raw water pump 6 and the suction flow rate and suction time by the suction pump 3.

[0057] By performing the above control, it becomes possible to accurately respond to the load fluctuation of the raw water, execute an efficient nitrification reaction and denitrification reaction, and perform good nitrogen removal.

[0058] (Second Embodiment) Hereinafter, a second embodiment of the present invention will be described in detail with reference to the drawings.

[0059] FIG. 4 is a diagram showing a change pattern of the dissolved oxygen concentration in the internal region 11 and the external region 12 of the partition plate 7 in the reaction tank 1 of the partition plate insertion type that repeats the overflow time zone and the overflow stop time zone at a constant interval time (15 minutes). Since the dissolved oxygen concentration fluctuates rapidly at the start of overflow, a simple control that makes the dissolved oxygen concentration a constant value cannot be applied, and it is necessary to perform accurate control according to the fluctuation of the dissolved oxygen concentration.

[0060] FIG. 5 is a flowchart showing the procedure of sewage treatment executed according to the second embodiment.

[0061] In this embodiment, first, in the first interval, a change pattern of the amount of dissolved oxygen (hereinafter referred to as DO amount) in the region where the membrane separation device 2 is disposed (the internal region 11 of the partition plate) is detected (S201). Here, as the change pattern to be detected, the maximum value (DO imax ) of the DO concentration in the internal region 11 of the partition plate in the first interval (the i-th interval) is used.

[0062] The change pattern of the DO amount in the internal region 11 is detected by a dissolved oxygen meter (DO meter) installed in the internal region 11. For more accurate control, the DO meter is installed near the center of the internal region 11, above the upper end of the membrane separation device 2, and at a position where the DO meter is immersed in the liquid even when the liquid level in the reaction tank 1 reaches the lowest water level.

[0063] Next, the detected maximum value (DO imax ) of the DO concentration is compared with a reference value, for example, 2 mg / L (S202). When the maximum value (DO imax ) of the DO concentration is 2 mg / L or less, the target value of the auxiliary aeration air volume in the second interval (the (i + 1)-th interval) is set based on the following formula (1) (S203).

[0064] (1) When DO imax ≦ 2 mg / L F i+1 = F i + (F max - F i ) × (DO high - DO imax ) / (DO high - DO low ) ··· (1) In formula (1), each symbol represents the following. F i : Auxiliary aeration air volume in the i-th interval F i+1 : Auxiliary aeration air volume in the (i + 1)-th interval F max : Maximum auxiliary aeration air volume (set, for example, equipment capacity) DO high: Upper limit target value of DO in the internal area (set, e.g., 2 mg / L) DO low : Lower limit target value of DO in the internal area (set, e.g., 1 mg / L) DO imax : Maximum value of DO in the internal area at the i-th interval

[0065] Also, when the maximum value of the DO concentration (DO imax ) exceeds 2 mg / L, the target value of the auxiliary aeration air volume at the second interval (the (i + 1)-th interval) is set based on the following formula (2) or formula (3) (S205).

[0066] (2) When DO imax > 2 mg / L F i+1 = F i × TDO high / T cycle × f ···(2) In formula (2), each symbol represents the following. TDO hgih : Time when DO in the internal area exceeds DO high T cycle : Time of one cycle f: Factor (e.g., 0.9)

[0067] F i+1 = F i × (DO high / DO imax ) ···(3) In formula (3), each symbol represents the following. DO high : Upper limit target value of DO in the internal area (set, e.g., 2 mg / L) DO imax : Maximum value of DO in the internal area at the i-th interval

[0068] Note that when DO imin (minimum value of DO in the internal area at the i-th interval) > 2 mg / L, it is also effective to add control with F i+1 = 0.

[0069] ​Next, in the second interval (the (i + 1)-th interval), the auxiliary aeration air volume from the auxiliary aeration means 5 is controlled to reach the set target value (S204, S206). As a method for controlling the auxiliary aeration air volume, there are a method of performing PID control by an air flow meter of the auxiliary aeration means 5 and an inverter of the auxiliary aeration blower B2 to approach the target value, and a method of setting the frequency of the inverter from the performance table of the blower B2 or the like to approach the target value.

[0070] In FIG. 4, the change pattern of the DO concentration in the overflow stop time zone reflects the oxygen consumption rate, and it is effective to utilize this change pattern of the DO concentration in the overflow stop time zone for the control of the auxiliary aeration air volume. Therefore, as the change pattern to be detected, the DO change pattern in the overflow stop time zone in the first interval is used, the excess or deficiency amount of the DO supply amount is set as the target value from the detected DO change pattern, and the auxiliary aeration air volume F in the second interval is calculated using this target value. i+1 can also be calculated.

[0071] Furthermore, it is also possible to perform image recognition on the change pattern of DO and / or the transition of the change pattern of DO (setting from ···, i - 2, i - 1, i to the (i + 1)-th) and determine the control amount by AI. It is also possible to measure the DO in the external region 12 together with the DO in the internal region 11 of the partition plate and perform control using both measured values.

[0072] By performing the control as described above, it is possible to accurately respond to the daily load fluctuations of sewage, efficiently execute the nitrification reaction and the denitrification reaction, and perform good nitrogen removal. In addition, it is possible to execute energy-saving sewage treatment with reduced auxiliary aeration air volume and suppressed power consumption.

[0073] In the present invention, by combining the second embodiment with the first embodiment, it is possible to more accurately respond to the daily load fluctuations of sewage, more efficiently execute the nitrification reaction and the denitrification reaction, and execute sewage treatment with further suppressed power consumption.

[0074] (Third Embodiment) Hereinafter, a third embodiment of the present invention will be described in detail with reference to the drawings. The third embodiment is a method for controlling the over-flow stop time in the second interval based on the ammonia nitrogen (NH4-N) concentration and / or the nitrate nitrogen (NO3-N) concentration in the internal region 11 in the first interval.

[0075] FIG. 6 is a flowchart showing a sewage treatment procedure in which control is executed based on the NH4-N concentration.

[0076] First, at the start time of over-flow in the first interval, the ammonia nitrogen (NH4-N) concentration in the internal region 11 is detected (S301). The NH4-N concentration in the internal region 11 can be detected by an NH4-N concentration meter C2 installed in the internal region 11. For more accurate control, the NH4-N concentration meter C2 is installed near the center of the internal region 11, above the upper end of the membrane separation device 2, and at a position where the NH4-N concentration meter C2 is immersed in the liquid even when the liquid level in the reaction tank 1 reaches the lowest level.

[0077] Next, the detected NH4-N concentration is compared with a reference value, for example, 3 mg / L (S302). In FIG. 4, in the over-flow time zone, since the DO is low (0.5 to 1 mg / L or less) in both the internal region 11 and the external region 12 of the partition plate, the nitrification reaction is inhibited. On the other hand, in the over-flow stop time zone, the DO in the internal region 11 of the partition plate becomes high and the nitrification reaction is promoted. Therefore, when the NH4-N concentration inside the partition plate at the start time of over-flow in the first interval (the i-th interval) exceeds the reference value (for example, 3 mg / L), in order to advance the nitrification reaction, as the target value of the over-flow stop time in the second interval (the (i + 1)-th interval), a long over-flow stop time corresponding to the exceeded amount is set (S303).

[0078] In the second interval, the breakthrough stop time is controlled to reach the target value (S304). Since the breakthrough stop time is the time when the water level in the reaction tank does not exceed the upper end of the partition plate 7, the breakthrough stop time can be controlled by detecting the water level with a water level sensor installed in the reaction tank and adjusting the flow rate of the raw water pump 6 while detecting the water level. Also, when the NH4-N concentration inside the partition plate at the breakthrough start time in the first interval (the i-th interval) is less than or equal to the reference value (for example, 3 mg / L), the sewage treatment in the second interval proceeds without controlling the breakthrough stop time.

[0079] Figure 7 is a flowchart showing the procedure of sewage treatment in which control is executed based on the NO3-N concentration.

[0080] First, at the breakthrough start time in the first interval, the concentration of nitrate nitrogen (NO3-N) in the internal region 11 is detected (S401). The NO3-N concentration in the internal region 11 can be detected by a NO3-N concentration meter C2 installed in the internal region 11. For more accurate control, the NO3-N concentration meter C2 is preferably installed near the center of the internal region 11, above the upper end of the membrane separation device 2, and at a position where the NO3-N concentration meter C2 is immersed in the liquid even when the liquid level in the reaction tank 1 reaches the lowest water level.

[0081] Next, the detected NO3-N concentration is compared with a reference value, for example, 5 mg / L (S402). When the NO3-N concentration inside the partition plate at the breakthrough start time in the first interval (the i-th interval) exceeds the reference value (for example, 5 mg / L), in order to suppress the nitrification reaction, a short breakthrough stop time corresponding to the exceeded amount is set as the target value of the breakthrough stop time in the second interval (the (i + 1)-th interval) (S403).

[0082] In the second interval, the breakthrough stop time is controlled to reach the target value (S404). The breakthrough stop time can be controlled by detecting the water level with a water level sensor installed in the reaction tank and adjusting the flow rate of the raw water pump 6. Further, when the NO3-N concentration inside the partition plate at the breakthrough start time in the first interval (the i-th interval) is equal to or lower than the reference value (for example, 5 mg / L), the sewage treatment in the second interval proceeds without controlling the breakthrough stop time.

[0083] In the present embodiment, the breakthrough stop time in the third interval (the (i + 2)-th interval) can also be controlled based on the values of the NH4-N concentration and / or the NO3-N concentration inside the partition plate at the breakthrough start times in the first interval (the i-th interval) and the second interval (the (i + 1)-th interval).

[0084] By performing the control as described above, it is possible to accurately respond to the daily load fluctuations of sewage, efficiently execute the nitrification reaction and the denitrification reaction, and perform good nitrogen removal. Further, the operation of the raw water pump 6 can be minimized, and energy-saving sewage treatment with suppressed power consumption can be executed.

[0085] In the present invention, by combining the third embodiment with the first and / or second embodiments, it is possible to more accurately respond to the daily load fluctuations of sewage, more efficiently execute the nitrification reaction and the denitrification reaction, and execute sewage treatment with further suppressed power consumption.

[0086] In the sewage treatment apparatus and the sewage treatment method according to the first to third embodiments described above, each means and step can be automatically controlled and executed using an information processing apparatus including a CPU, a RAM, a ROM, an HDD, and a data input unit.

[0087] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

Explanation of Reference Numerals

[0088] 1 Reaction tank 2 Membrane separation device 3 Suction pump 4 Diffuser pipe 5 Auxiliary aeration means 6 Raw water pump 7 Partition board 8 Flow adjustment tank 9 Raw water tank 10 Sewage treatment device 11 Internal region 12 External region DO Dissolved oxygen meter C1 Raw water component concentration meter C2 NH4-N / NO3-N concentration meter

Claims

Claim 1: Inside a reaction tank for treating sewage, there are provided a membrane separation device for separating contaminants contained in the sewage, an air diffuser for supplying air bubbles to the membrane separation device, and a partition plate for partitioning the area where the membrane separation device is disposed and other areas. Means for presetting target values of at least one control item selected from an interval time, an overflow time ratio, an overflow water depth, an operation method of a raw material pump, and an operation method of a suction pump according to load fluctuations of sewage supplied to the sewage treatment device. Means for detecting load fluctuations of sewage supplied to the sewage treatment device. Means for controlling at least one control item to reach a preset target value based on the detected load fluctuations. In a sewage treatment device comprising the above, Means for detecting a change pattern of the dissolved oxygen amount in the area where the membrane separation device is disposed in a first interval. Means for setting a target value of the auxiliary aeration air volume in a second interval based on the detected change pattern. Means for controlling the auxiliary aeration air volume to reach the target value in a second interval. A sewage treatment device characterized by comprising the above. Claim 2: Inside a reaction tank for treating sewage, there are provided a membrane separation device for separating contaminants contained in the sewage, an air diffuser for supplying air bubbles to the membrane separation device, and a partition plate for partitioning the area where the membrane separation device is disposed and other areas. Means for presetting target values of at least one control item selected from an interval time, an overflow time ratio, an overflow water depth, an operation method of a raw material pump, and an operation method of a suction pump according to load fluctuations of sewage supplied to the sewage treatment device. Means for detecting load fluctuations of sewage supplied to the sewage treatment device. Means for controlling at least one control item to reach a preset target value based on the detected load fluctuations. In a sewage treatment device comprising the above, Means for detecting the ammonia nitrogen (NH₄-N) concentration and / or the nitrate nitrogen (NO₃-N) concentration in the area where the membrane separation device is disposed at the start time of overflow in a first interval. Means for setting a target value of the overflow stop time in a second interval based on the detected concentration. Means for controlling the overflow stop time to reach the target value in a second interval. A sewage treatment device characterized by comprising the above. Claim 3 Inside a reaction tank for treating sewage, there are a membrane separation device for separating contaminants contained in the sewage, an air diffuser for supplying air bubbles to the membrane separation device, and a partition plate for partitioning the area where the membrane separation device is disposed from other areas. In a sewage treatment apparatus comprising the same, means for detecting a change pattern of the amount of dissolved oxygen in the area where the membrane separation device is disposed in a first interval; means for setting a target value of the auxiliary aeration air volume from the auxiliary aeration means in a second interval based on the detected change pattern; means for controlling the auxiliary aeration air volume to be the target value in a second interval; A sewage treatment apparatus, characterized by comprising the above.

4. Means for detecting the concentration of ammonia nitrogen (NH ４ -N) and / or nitrate nitrogen (NO ３ -N) in the region where the membrane separation device is disposed at the start time of the breakthrough in the first interval; means for setting a target value of the overflow stop time in a second interval based on the detected concentration; means for controlling the overflow stop time to be the target value in a second interval; The sewage treatment apparatus according to claim 3, comprising the above.

5. Inside a reaction tank for treating sewage, there are a membrane separation device for separating contaminants contained in the sewage, an air diffuser for supplying air bubbles to the membrane separation device, and a partition plate for partitioning the area where the membrane separation device is disposed from other areas. In a sewage treatment apparatus comprising the same, Means for detecting the concentration of ammonia nitrogen (NH ４ -N) and / or nitrate nitrogen (NO ３ -N) in the region where the membrane separation device is disposed at the start time of the breakthrough in the first interval; means for setting a target value of the overflow stop time in a second interval based on the detected concentration; means for controlling the overflow stop time to be the target value in a second interval; A sewage treatment apparatus, characterized by comprising the above.

6. In a sewage treatment method using the sewage treatment apparatus according to claim 1 or 2, a step of presetting a target value of at least one control item selected from an interval time, an overflow time ratio, an overflow water depth, an operation method of a raw water pump, and an operation method of a suction pump according to a load fluctuation of sewage supplied to the sewage treatment apparatus; a step of detecting a load fluctuation of sewage supplied to the sewage treatment apparatus; a step of controlling the at least one control item to be a preset target value based on the detected load fluctuation; A sewage treatment method, characterized by comprising the above.

7. In a sewage treatment method using the sewage treatment apparatus according to claim 1 or 3, a step of detecting a change pattern of the amount of dissolved oxygen in the area where the membrane separation device is disposed in a first interval; Based on the detected change pattern, setting a target value for the auxiliary aeration air volume from the auxiliary aeration means in the second interval; In the second interval, controlling the auxiliary aeration air volume to be the target value; A sewage treatment method characterized by comprising the above.

8. In the sewage treatment method using the sewage treatment apparatus according to claim 2, 4 or 5, Step of detecting ammonia nitrogen (NH ４ -N) concentration and / or nitrate nitrogen (NO ３ -N) concentration in the region where the membrane separation device is arranged at the start time of the breakthrough in the first interval; Based on the detected concentration, setting a target value for the overflow stop time in the second interval; In the second interval, controlling the overflow stop time to be the target value; A sewage treatment method characterized by comprising the above.

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