Activated sludge treatment device and method for modifying activated sludge treatment device

Abstract

To make an external circulation device smaller than a conventional device, in a membrane separation activated sludge treatment device.SOLUTION: An activated sludge treatment device 1 of the present invention includes: a biological treatment tank 10 including an anaerobic region 20 into which nitrogen-containing organic wastewater is introduced, and an aerobic region 30 located downstream of the anaerobic region 20, the anaerobic region 20 and the aerobic region 30 being separated by at least one partition member 11; a membrane treatment tank 50 located downstream of the aerobic region 30 and having a submerged membrane separation device 51; an aeration device 60 for aerating each of the aerobic region 30 and the membrane treatment tank 50; an external circulation device 70 that returns activated sludge mixed water in the membrane treatment tank 50 to the anaerobic region 20; and an internal circulation device 80 that returns the activated sludge mixed water in the aerobic region 30 to the anaerobic region 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an activated sludge treatment apparatus and a method for modifying an activated sludge treatment apparatus. [Background technology]

[0002] There are known organic wastewater treatment methods and treatment equipment that biologically treat nitrogen-containing organic wastewater using activated sludge, followed by a solid-liquid separation process in a membrane treatment tank to obtain membrane-treated water. This type of organic wastewater treatment method is called the membrane bioreactor (MBR) process, and can be broadly divided into two types: an integrated type in which the membrane separation device is installed directly in the aerobic tank of the biological treatment tank, and a separate tank type in which the biological treatment tank and membrane treatment tank are installed separately. The separate tank type allows the biological treatment tank and membrane treatment tank to be installed separately, making it useful in cases where the installation space for the activated sludge treatment equipment is limited.

[0003] One such example of a separate-tank type activated sludge treatment device is disclosed in Japanese Patent Laid-Open Publication No. 2017-12995 (Patent Document 1). In Patent Document 1, a circulation path is provided for extracting the treated water downstream of the membrane treatment tank and circulating it to an anoxic tank, and a portion of the treated water in the membrane treatment tank is pumped to the anoxic tank. As a result, nitrate nitrogen (activated sludge mixed liquor) nitrified by aerobic treatment in the membrane treatment tank is supplied to the anoxic tank, where it is removed as nitrogen by denitrification. This return of the activated sludge mixed liquor not only circulates nitrate nitrogen but also serves to equalize the activated sludge concentration (MLSS). External circulation is performed between the membrane treatment tank, which is the final destination of the activated sludge, and the anoxic tank. In particular, in separate-tank types, the biological treatment tank and the membrane treatment tank are often installed separately, necessitating an external circulation device for external circulation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-12995 Summary of the Invention [Problem to be solved by the invention]

[0005] Due to the characteristics of the membrane separation filtration device, the membrane bioreactor (MBR) requires a larger amount of circulating water (for example, about three times the treatment capacity) than other biological treatment methods (for example, circulating nitrification and denitrification).As a result, the circulating pumps and piping that make up the external circulation device also need to have a large treatment capacity, which increases the size of the external circulation device, and so there were cases where conventional membrane bioreactor treatment devices could not be installed because there was not enough space to install the external circulation device.

[0006] Therefore, in membrane separation activated sludge treatment devices, it is desired to make the external circulation device smaller than before. [Means for solving the problem]

[0007] The activated sludge treatment apparatus of the present invention is an activated sludge treatment apparatus comprising: a biological treatment tank including an anaerobic region into which nitrogen-containing organic wastewater is introduced; and an aerobic region located downstream of the anaerobic region, the anaerobic region and the aerobic region being separated by at least one partition member; a membrane treatment tank located downstream of the aerobic region and having a submerged membrane separation device; and an aeration device that aerates each of the aerobic region and the membrane treatment tank, and is characterized by comprising an external circulation device that returns the activated sludge mixed water in the membrane treatment tank to the anaerobic region; and an internal circulation device that returns the activated sludge mixed water in the aerobic region to the anaerobic region.

[0008] The method for modifying an activated sludge treatment apparatus according to the present invention is a method for modifying an activated sludge treatment apparatus comprising: a biological treatment tank including an anaerobic zone into which nitrogen-containing organic wastewater is introduced, and an aerobic zone located downstream of the anaerobic zone, the anaerobic zone and the aerobic zone being separated by at least one partition member; a membrane treatment tank located downstream of the aerobic zone and having a submerged membrane separation device; an aeration device that aerates each of the aerobic zone and the membrane treatment tank; and an external circulation device that returns the activated sludge mixed water in the membrane treatment tank to the anaerobic zone, and is characterized by comprising an internal circulation device installation step of installing an internal circulation device that returns the activated sludge mixed water in the aerobic zone to the anaerobic zone.

[0009] According to these configurations, an internal circulation device is provided in the biological treatment tank, and internal circulation is performed to return the activated sludge mixed water in the aerobic region to the anaerobic region, thereby reducing the amount of circulating water in the external circulation and making the external circulation device, such as the circulation pump and transfer piping, smaller than conventional devices.

[0010] Preferred embodiments of the present invention will be described below, but the scope of the present invention is not limited to the preferred embodiments described below.

[0011] In the activated sludge treatment device according to the present invention, it is preferable that the volume of the anoxic region is larger than the volume of the aerobic region.

[0012] With this configuration, even if the activated sludge concentration in the anoxic region becomes low, it is easy to ensure the absolute amount of activated sludge (biomass) required for denitrification treatment in the anoxic region, and the overall amount of circulating water due to internal and external circulation can be reduced.

[0013] In the activated sludge treatment apparatus according to the present invention, the ratio of the volume of the aerobic region to the volume of the anoxic region is preferably in the range of 1:1.1 to 1.5.

[0014] With this configuration, even if the activated sludge concentration in the anoxic region becomes low, it is easy to ensure the absolute amount of activated sludge (biomass) required for denitrification treatment in the anoxic region, and the overall amount of circulating water due to internal and external circulation can be reduced.

[0015] In the activated sludge treatment apparatus according to the present invention, the internal circulation device preferably includes an air lift pump installed in the aerobic region.

[0016] According to this configuration, internal circulation is performed by an air lift pump that can be installed in the aerobic region, so new space is unlikely to be required for installing an internal circulation pump.

[0017] The activated sludge treatment apparatus according to the present invention preferably further comprises an anaerobic zone separated by a partition member before the anoxic zone.

[0018] According to this configuration, the biological treatment tank further includes an anaerobic region, so that phosphorus can be effectively removed from organic wastewater containing nitrogen and phosphorus.

[0019] In the activated sludge treatment device of the present invention, it is preferable that the biological treatment tank has the anaerobic zones and the aerobic zones separated by at least three partition members arranged alternately from the front to the rear, and the membrane treatment tank is arranged at least after the last aerobic zone.

[0020] According to this configuration, the amount of circulating water in the external circulation can be reduced in a multi-stage membrane bioreactor, and the external circulation equipment such as the circulation pump and transfer piping can be made smaller than before.

[0021] It is preferable that the method for modifying an activated sludge treatment device according to the present invention further includes a partition member relocation step of removing the partition member in the biological treatment tank and relocating the partition member to a position where the volume of the anaerobic region is larger than the volume of the aerobic region.

[0022] With this configuration, even if the activated sludge concentration in the anoxic region becomes low, it is easy to ensure the absolute amount of activated sludge (biomass) required for denitrification treatment in the anoxic region, and the overall amount of circulating water due to internal and external circulation can be reduced.

[0023] Further features and advantages of the present invention will become more apparent from the following description of exemplary and non-limiting embodiments, which is given with reference to the drawings. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic view of an activated sludge treatment apparatus (after modification) according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of a membrane cartridge provided in the membrane separation device of FIG. 1. [Figure 3] FIG. 2 is a schematic diagram of the activated sludge treatment device before modification. [Figure 4] FIG. 10 is a schematic view of the activated sludge treatment device after the partition member moving step. [Figure 5] FIG. 4 is a schematic view of an activated sludge treatment apparatus according to a second embodiment of the present invention. [Figure 6] FIG. 10 is a schematic view of an activated sludge treatment apparatus according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] A first embodiment of an activated sludge treatment apparatus and a method for modifying an activated sludge treatment apparatus according to the present invention will be described with reference to the drawings. The following describes an activated sludge treatment apparatus 1 as one embodiment of the activated sludge treatment apparatus according to the present invention, and a method for modifying a conventional activated sludge treatment apparatus 100 into the activated sludge treatment apparatus 1. In the following description, the term "treated water" refers to water treated in each tank and upstream of each zone, regardless of the level of treatment. The term "membrane-treated water" refers to filtered water treated in a membrane treatment tank. The term "activated sludge-mixed water" refers to water mixed with activated sludge in each tank and zone, regardless of the level of treatment. The term "external circulation" refers to circulation between tanks, such as from the membrane treatment tank 50 to the biological treatment tank 10, and the term "internal circulation" refers to circulation between zones within the same tank.

[0026] [Configuration of activated sludge treatment equipment] As shown in Fig. 1, the activated sludge treatment apparatus 1 according to this embodiment is an apparatus that biologically treats nitrogen-containing organic wastewater in a treatment tank storing activated sludge, and the treatment tank includes a biological treatment tank 10 and a membrane treatment tank 50. In this embodiment, the biological treatment tank 10 is partitioned into an anoxic region 20 and an aerobic region 30 by a single partition member 11. Thus, the activated sludge treatment apparatus 1 according to this embodiment is a single-stage circulation type membrane separation activated sludge treatment apparatus in which the biological treatment tank 10 includes one anoxic region 20 and one aerobic region 30.

[0027] Nitrogen-containing organic wastewater is organic wastewater such as sewage, human waste from which solids have been removed, and wastewater discharged from factories, and contains organic components including nitrogen. Nitrogen-containing organic wastewater is preferably pretreated to remove solids using a filter or the like before being introduced into the biological treatment tank 10, but the presence or absence of pretreatment and the type of pretreatment are not particularly limited in the present invention.

[0028] The anoxic region 20 is a region into which nitrogen-containing organic wastewater is introduced. In the anoxic region 20, the organic wastewater is mixed with activated sludge under anaerobic conditions by an agitator (not shown) and anaerobically treated. The activated sludge mixed water in the anoxic region 20 includes activated sludge mixed water returned from the external circulation device 70 and internal circulation device 80, which will be described later. In the anoxic region 20, nitrate nitrogen and nitrite nitrogen (collectively referred to as nitrate nitrogen, etc.) are anaerobically treated by anaerobic microorganisms (here, denitrifying bacteria) contained in the activated sludge and reduced to nitrogen gas. The nitrogen gas is released into the atmosphere, and the activated sludge mixed water in the anoxic region 20 is denitrified.

[0029] The partition member 11 is a partition wall that separates the biological treatment tank 10 into an anaerobic region 20 and an aerobic region 30. The partition member 11 separates the anaerobic region 20 and the aerobic region 30 in a manner that allows at least treated water that has been treated in the anoxic region 20 to flow from the anoxic region 20 into the aerobic region 30. In this embodiment, the partition member 11 has an opening (not shown), and treated water that has been anaerobically treated in the anoxic region 20 flows into the aerobic region 30 through the opening of the partition member 11. The configuration and material of the partition member 11 are not particularly limited. For example, synthetic wood, steel, etc. may be used as the material.

[0030] The aerobic zone 30 is located after the anoxic zone 20 in the biological treatment tank 10. The aerobic zone 30 receives at least a portion of the treated water from the anoxic zone 20. The activated sludge mixed water in the aerobic zone 30 is aerobically treated by aerobic microorganisms contained in the activated sludge under aerobic conditions. Specifically, the activated sludge mixed water in the aerobic zone 30 is aerated by the aeration device 60, which will be described later, so that the ammonia nitrogen contained in the activated sludge mixed water is oxidized (i.e., nitrified) by the aerobic microorganisms to become nitrate nitrogen, etc.

[0031] The membrane treatment tank 50 is disposed downstream of the aerobic region 30 of the biological treatment tank 10. In this embodiment, the aerobic region 30 of the biological treatment tank 10 and the membrane treatment tank 50 are connected by a connecting pipe 40. There are no particular limitations on the method of conveying water from the aerobic region 30 to the membrane treatment tank 50, but in this embodiment, when membrane-treated water is sucked from the membrane separation device 51, a water level difference occurs between the aerobic region 30 and the membrane treatment tank 50, and this water level difference is utilized to allow the treated water to flow into the membrane treatment tank 50 without power. The membrane treatment tank 50 is a tank that performs solid-liquid separation of the treated water that has flowed in from the aerobic region 30 of the biological treatment tank 10 to produce membrane-treated water, and has a submerged membrane separation device 51 inside.

[0032] The activated sludge treatment apparatus 1 includes an aeration device 60 that aerates each of the aerobic region 30 of the biological treatment tank 10 and the membrane treatment tank 50. By supplying air (oxygen) from the aeration device 60, the activated sludge mixed water in the aerobic region 30 and the membrane treatment tank 50 is kept under aerobic conditions. In this embodiment, the aeration device 60 includes a blower 61 that is a compressed air generator, two aeration members 62, and an aeration pipe 63 that connects these members together. Air (oxygen) is supplied to the aerobic region 30 and the membrane treatment tank 50 from the aeration members 62 that are installed near the bottom of the aerobic region 30 and the membrane treatment tank 50, respectively. As the aeration member 62, a membrane-type aeration member, an aeration pipe, or the like is used.

[0033] As described above, the membrane treatment tank 50 is equipped with a membrane separation device 51 therein. The membrane separation device 51 includes a plurality of membrane cartridges 52, a header pipe (described later), a suction pump (not shown), and the like. The plurality of membrane cartridges 52 are arranged and housed at regular intervals in the membrane treatment tank 50 so that each membrane surface is in a vertical position. The number of membrane cartridges 52 arranged and housed in the membrane treatment tank 50 is not particularly limited, and one or more may be provided.

[0034] FIG. 2 shows a membrane cartridge 52. The membrane cartridge 52 is configured by disposing separation membranes 52b on both the front and back sides of a resin membrane support 52a equipped with a water collection pipe 52c. In this embodiment, one membrane cartridge 52 is equipped with two water collection pipes 52c, and the separation membrane 52b is configured as a microfiltration membrane having a nominal pore size of approximately 0.4 μm and comprising an organic polymer membrane with porosity on the surface of a nonwoven fabric. A header pipe (not shown) that collects membrane-filtered water from the multiple membrane cartridges 52 is connected to the water collection pipe 52c, and the membrane-treated water is sucked in by a suction pump (not shown) connected to the header pipe. The membrane-treated water is discharged into a river or the like after undergoing other treatments as necessary.

[0035] The type of separation membrane 52b and the membrane cartridge 52 are not limited to the above-described embodiments, and any type of separation membrane and any form of membrane cartridge (hollow fiber membrane cartridge, tubular membrane cartridge, monolith membrane cartridge, etc.) can be used.

[0036] The air bubbles supplied from the air diffuser 62 of the aeration device 60 installed below the multiple membrane cartridges 52 of the membrane separation device 51 and the upward flow caused by the air bubbles prevent sludge from adhering to the membrane surface, and the adhering sludge is removed from the membrane surface. In other words, the air (oxygen) supplied from the air diffuser 62 of the membrane treatment tank 50 serves both the function of cleaning the membrane surfaces of the membrane cartridges 52 and the function of aerobic treatment.

[0037] The activated sludge treatment apparatus 1 is equipped with an external circulation device 70 that returns the activated sludge mixed water in the membrane treatment tank 50 to the anoxic region 20 of the biological treatment tank 10. The external circulation device 70 has an external circulation pump 71 and transfer piping 72. The external circulation device 70 returns the activated sludge mixed water that has not been subjected to membrane separation treatment in the membrane treatment tank 50 to the anoxic region 20. Since this activated sludge mixed water in the membrane treatment tank 50 contains a large amount of nitrate nitrogen and the like, it is denitrified in the anoxic region 20 and removed as nitrogen gas. Along with the circulation of nitrate nitrogen and the like, the activated sludge in the membrane treatment tank 50 is also returned to the anoxic region 20 to equalize the activated sludge concentration (MLSS).

[0038] The activated sludge treatment apparatus 1 according to the present invention includes, in addition to the external circulation device 70, an internal circulation device 80 that returns the activated sludge mixed water in the aerobic region 30 of the biological treatment tank 10 to the anoxic region 20.

[0039] As shown in Figure 3, a conventional activated sludge treatment device 100 only performs external circulation, returning activated sludge mixed water in the membrane treatment tank 50, which is the final stage of activated sludge treatment, to the anoxic region 20. This is because the membrane treatment tank 50 is a tank that performs membrane separation and also an aerobic treatment tank that performs aerobic treatment, and it has been thought that it is efficient to nitrify as much ammonia nitrogen as possible into nitrate nitrogen and the like in the membrane treatment tank 50 before returning it to the anoxic region 20. However, the present inventors have discovered that the amount of water circulated in the external circulation can be reduced by using an internal circulation system in which the activated sludge mixed water in the aerobic region 30 is returned to the anoxic region 20 in combination with external circulation to circulate nitrate nitrogen and activated sludge. In other words, they have discovered that by using internal circulation in combination, the nitrogen concentration flowing into the anoxic region 20 and the nitrogen removal rate in the anoxic region 20 can be ensured without circulating all of the activated sludge mixed water through external circulation. According to the present invention, the external circulation device, such as the external circulation pump 71 and the transfer piping 72, can be made smaller than before, so that it becomes possible to install an activated sludge treatment device in a place where it was previously not possible to install an activated sludge treatment device because it was not possible to secure the space for installing the external circulation pump or the space for laying the transfer piping, etc. In other words, when an external circulation device of the same scale as before is used, it is possible to improve the nitrogen removal rate by using the internal circulation device 80 in combination.

[0040] The internal circulation device 80 has an internal circulation pump 81 and a transfer pipe 82. In this embodiment, an air lift pump that lifts water by the upward movement of air supplied from a blower or the like is used as the internal circulation pump 81, and the air lift pump is set in the aerobic region 30.

[0041] In this embodiment, the volume of the anoxic region 20 is set larger than the volume of the aerobic region 30 in the biological treatment tank 10. Specifically, the ratio of the volume of the aerobic region 30 to the volume of the anoxic region 20 is set in the range of 1:1.1 to 1.5.

[0042] In this embodiment, the biological treatment tank 10 is equipped with an internal circulation device 80, which performs internal circulation from the aerobic region 30 to the anoxic region 20. This reduces the amount of circulated water required for external circulation. Without the internal circulation device 80, the external circulation device 70 requires a circulated water volume approximately three times its treatment capacity. However, with the internal circulation device 80, the ratio of the internal circulated water volume to the external circulated water volume can be set to, for example, 1.0-2.0:2.0-1.0. As a result, the amount of circulated water required for external circulation can be reduced to approximately one-third to two-thirds of the conventional amount, and the size of the external circulation device 70 (external circulation pump 71, transfer piping 72, etc.) can also be reduced. Furthermore, with the activated sludge treatment device 1 of this embodiment, the nitrogen concentration of the inflow into the anoxic region 20 can be set to a range of 30-40 mg / L, achieving a nitrogen removal rate of 60-70%.

[0043] Furthermore, in the biological treatment tank 10, the volume of the anoxic region 20 is larger than the volume of the aerobic region 30, so it is easy to secure the activated sludge (biomass) necessary for denitrification treatment even if the activated sludge concentration (MLSS) in the anoxic region 20 becomes low. As a result, the activated sludge treatment device 1 can also reduce the overall amount of circulating water due to internal and external circulation.

[0044] [Method for modifying activated sludge treatment equipment] Next, with reference to Figures 1, 3, and 4, a method of modifying an existing activated sludge treatment apparatus 100 shown in Figure 3 to the activated sludge treatment apparatus 1 shown in Figure 1 will be described. In Figures 3 and 4, members having the same functions as those in Figure 1 are designated by the same reference numerals, and their description will be omitted.

[0045] When renovating or updating an activated sludge treatment plant, it is necessary to consider the layout of each tank and device within the limited framework of the structure. In such cases, the installation space for the external circulation device may be smaller than that of the existing activated sludge treatment plant 100, which may result in the problem of not being able to install the activated sludge treatment plant itself. This modification method can be used in such cases.

[0046] 3 shows an existing activated sludge treatment apparatus 100, which comprises a biological treatment tank 10, in which an anaerobic region 20, into which nitrogen-containing organic wastewater is introduced, and an aerobic region 30, which is located downstream of the anoxic region 20 and can receive treated water from the anoxic region 20, are separated by at least one partition member 11, and a membrane treatment tank 50 having a submerged membrane separation device 51 that separates the treated water flowing in from the aerobic region 30 into solids and liquids.The apparatus also comprises an aeration device 60 that aerates both the aerobic region 30 and the membrane treatment tank 50, and an external circulation device 75 that returns the activated sludge mixed water in the membrane treatment tank 50 to the anoxic region 20.

[0047] The existing activated sludge treatment device 100 does not have the above-mentioned internal circulation device 80 in the biological treatment tank 10, and the ratio of the volume of the anoxic region 20 to the volume of the aerobic region 30 is approximately 1:1.

[0048] (Partition member relocation process) First, the operation of the existing activated sludge treatment device 100 is stopped, the liquid to be treated is discharged from the biological treatment tank 10, and the partition member 11 is temporarily removed. Next, the partition member 11 is moved to a position where the volume of the anaerobic region 20 is larger than the volume of the aerobic region 30 (in this embodiment, a position where the volume ratio of the anaerobic region 20 to the aerobic region 30 is 1.5:1) (FIG. 4). Thereafter, the position of the aeration member 62 is adjusted as necessary.

[0049] (Internal circulation device installation process) Next, an internal circulation device installation step is performed in which an internal circulation device 80 that returns the activated sludge mixed water in the aerobic region 30 to the anoxic region 20 is installed in the activated sludge treatment device 100 of FIG.

[0050] In the internal circulation device installation step of this embodiment, an air lift pump that uses the rising air supplied from a blower or the like to lift water is installed as the internal circulation pump 81 in the aerobic region 30, and a transfer pipe 82 that is connected to the internal circulation pump 81 and extends from the aerobic region 30 to the anoxic region 20 is installed. Finally, the external circulation pump 76 and transfer pipe 77 that make up the external circulation device 75 are replaced with the smaller external circulation pump 71 and transfer pipe 72, and an external circulation device 70 that is smaller overall in size than the external circulation device 75 is installed. In this way, the activated sludge treatment device 1 shown in FIG. 1 is modified.

[0051] According to the method for modifying the activated sludge treatment device 100 of this embodiment, by installing a new internal circulation device 80 in the internal circulation device installation step, the external circulation device 75 can be reduced in size from the existing one. Moreover, in this embodiment, an air lift pump that can be installed in the upper region of the aerobic region 30 is installed as the internal circulation pump 81, which has the advantage that no new space is required to install the internal circulation device 80. An air lift pump also has the advantage of relatively low power consumption.

[0052] Furthermore, the partition member relocation step relocates the partition member 11, making the volume of the anoxic region 20 larger than the volume of the aerobic region 30. This makes it easy to ensure the absolute amount of activated sludge (biomass) necessary for denitrification treatment even if the activated sludge concentration (MLSS) in the anoxic region 20 decreases, and reduces the overall amount of circulating water (internal circulation and external circulation) in the activated sludge treatment device 1. Therefore, it is easy to modify the existing activated sludge treatment device 100 to have a smaller external circulation device while still utilizing the external shape of the biological treatment tank 10.

[0053] Next, a second embodiment of an activated sludge treatment apparatus according to the present invention will be described with reference to Fig. 5. An activated sludge treatment apparatus 2 will be described below as one embodiment of the activated sludge treatment apparatus according to the present invention.

[0054] The activated sludge treatment device 2 according to the second embodiment differs from the first embodiment in the biological treatment tank 15. The biological treatment tank 15 is partitioned by at least three partition members 11, and anoxic regions 20 (20A, 20B) and aerobic regions 30 (30A, 30B) are alternately arranged from the front to the rear. That is, the activated sludge treatment device 2 according to the second embodiment is a multi-stage membrane bioreactor, and this embodiment shows an example in which the anoxic regions 20 and the aerobic regions 30 are alternately arranged in two stages. The biological treatment tank 15 may also be a multi-stage step type in which the anoxic regions 20 and the aerobic regions 30 are alternately arranged in three or four or more stages.

[0055] In the second embodiment, the volume of the anaerobic region 20 (20A, 20B) is also larger than the volume of the aerobic region 30 (30A, 30B), and the volume ratio of the anaerobic region 20 (20A, 20B) to the aerobic region 30 (30A, 30B) is 1.5:1.0, respectively.

[0056] Nitrogen-containing organic wastewater is introduced into both the first-stage anaerobic zone 20A and the second-stage anaerobic zone 20B. The first-stage aerobic zone 30A, the second-stage aerobic zone 30B, and the membrane treatment tank 50 are all equipped with aeration members 62 near their bottoms, and the activated sludge mixed water in each zone is aerated.

[0057] In the second embodiment, the membrane treatment tank 50 is disposed downstream of the final aerobic zone 30B, and performs solid-liquid separation on the treated water that flows in from the final aerobic zone 30B. In this manner, the membrane treatment tank 50 is disposed at least downstream of the final aerobic zone 30B.

[0058] In the second embodiment, the external circulation device 70 returns the activated sludge mixed water in the membrane treatment tank 50 to the second-stage anoxic region 20B of the biological treatment tank 10. The internal circulation device 80 returns the activated sludge mixed water in the first-stage aerobic region 30A to the first-stage anoxic region 20A.

[0059] Furthermore, the second embodiment includes a second internal circulation device 90 that returns the activated sludge mixed water in the second-stage anoxic region 20B to the first-stage anoxic region 20A. The second internal circulation device 90 has a second internal circulation pump 91 and a transfer pipe 92. In this embodiment, an air lift pump, for example, is used as the second internal circulation pump 91. The air introduced by the air lift pump is a small amount and has coarse bubbles that are difficult to dissolve in the mixed water, so it can also be used for internal circulation in the anoxic region.

[0060] Even in a multi-stage membrane bioreactor such as the activated sludge treatment device 2 of the second embodiment, the internal circulation from the aerobic region 30 to the anoxic region 20 is performed by the internal circulation device 80, thereby reducing the amount of circulating water in the external circulation and enabling the external circulation device 70 to be smaller than conventional devices. A multi-stage or multi-step system can achieve a higher nitrogen removal rate than a single-stage system. For example, a single-stage system achieves a nitrogen removal rate of 60-70%, while a two-stage system can achieve a nitrogen removal rate of 70% or more. In the multi-stage membrane bioreactor of the second embodiment, when the internal circulation device 80 is not provided and internal circulation is not performed, the external circulation device 70 requires a circulating water volume approximately three times the treatment capacity. However, when the internal circulation device 80 is provided, the ratio of the internal circulating water volume (in the internal circulation device 80) to the external circulating water volume can be set to a ratio of 1.0-2.0:2.0-1.0, respectively. As a result, the amount of external circulating water can be reduced to approximately one-third to two-thirds of that in conventional systems, and the size of the external circulation device 70 can also be reduced.

[0061] As an example of the amount of circulating water in the activated sludge treatment device 2 of the second embodiment, of the inflow amount of nitrogen-containing organic wastewater of 1Q, 0.5Q is introduced into the first-stage anaerobic region 20A, 0.5Q is introduced into the second-stage anaerobic region 20B, the inflow amount from the second-stage aerobic region 30B to the membrane treatment tank 50 is set to 2Q, the amount of external circulating water from the membrane treatment tank 50 to the second-stage anaerobic region 20B is set to 1Q, the amount of internal circulating water from the second-stage anaerobic region 20B to the first-stage anaerobic region 20A is set to 0.5Q, and the amount of internal circulating water from the first-stage aerobic region 30A to the first-stage anaerobic region 20A is set to 0.5Q, and finally, 1Q of membrane-treated water is obtained from the membrane treatment tank 50.

[0062] In the second embodiment, a second internal circulation device 90 is further provided, which also performs internal circulation from the anoxic region 20B to the anoxic region 20A, so that the external circulation device 70 can return the activated sludge mixed water in the membrane treatment tank 50 to the second anoxic region 20B of the biological treatment tank 10. With this configuration, the length of the transfer piping 72 of the external circulation device 70 does not need to be long in a multi-stage membrane bioreactor, and a smaller treatment capacity external circulation pump 71 can be used, making it easier to further reduce the size of the external circulation device 70. However, in the second embodiment, the external circulation device 70 may be configured to return the activated sludge mixed water in the membrane treatment tank 50 to the first anoxic region 20A of the biological treatment tank 10, in which case the second internal circulation device 90 need not be installed.

[0063] In the second embodiment, the volumes of the anoxic regions 20A and 20B in the biological treatment tank 10 are also larger than the volumes of the aerobic regions 30A and 30B, so that it is easy to secure the activated sludge (biomass) necessary for denitrification treatment even if the activated sludge concentration (MLSS) in the anoxic region 20 decreases. This makes it possible to reduce the overall amount of circulating water in the activated sludge treatment device 1.

[0064] Next, a third embodiment of an activated sludge treatment apparatus according to the present invention will be described with reference to Fig. 6. An activated sludge treatment apparatus 3 will be described below as one embodiment of the activated sludge treatment apparatus according to the present invention.

[0065] The activated sludge treatment device 3 of the third embodiment has a biological treatment tank 16 that is different from the biological treatment tank 15 of the activated sludge treatment device 2 of the second embodiment. The biological treatment tank 16 of the activated sludge treatment device 3 has an anaerobic region 25 further separated by a partition member 11 in front of the anoxic region 20A. At least a portion of the nitrogen-containing organic wastewater is introduced into the anoxic region 20A through the anaerobic region 25.

[0066] In this embodiment, at least a portion of the nitrogen-containing organic wastewater is introduced into the anaerobic region 25 and then introduced into the anoxic region 20A via the anaerobic region 25. The remainder of the nitrogen-containing organic wastewater is introduced into the anoxic region 20B.

[0067] In the activated sludge treatment apparatus 3 of the third embodiment, the external circulation device 70 also returns the activated sludge mixed water in the membrane treatment tank 50 to the second-stage anoxic region 20B of the biological treatment tank 10. The internal circulation device 80 returns the activated sludge mixed water in the first-stage aerobic region 30A to the first-stage anoxic region 20A.

[0068] In the third embodiment, instead of the second internal circulation device 90, a third internal circulation device 95 is provided that returns the activated sludge mixed water in the second-stage anoxic region 20B to the anaerobic region 25. The third internal circulation device 95 has a third internal circulation pump 96 and a transfer pipe 97. In this embodiment, an air lift pump, for example, is used as the third internal circulation pump 96.

[0069] The third embodiment also includes a fourth internal circulation device 98 that returns the activated sludge mixed water in the first-stage anoxic region 20A to the anaerobic region 25. Although not shown, the fourth internal circulation device 98 also has a fourth internal circulation pump and transfer piping.

[0070] As an example of the amount of circulated water in the activated sludge treatment device 3 of the third embodiment, of the inflow amount of nitrogen-containing organic wastewater of 1Q, 0.5Q is introduced into the anaerobic region 25, 0.5Q is introduced into the second-stage anaerobic region 20B, the inflow amount from the second-stage aerobic region 30B to the membrane treatment tank 50 is set to 2.5Q, the external circulating water amount from the membrane treatment tank 50 to the second-stage anaerobic region 20B is set to 1.5Q, the internal circulating water amount from the second-stage anaerobic region 20B to the anaerobic region 25 is set to 0.5Q, the internal circulating water amount from the first-stage aerobic region 30A to the first-stage anaerobic region 20A is set to 0.5Q, and the internal circulating water amount from the first-stage anaerobic region 20A to the anaerobic region 25 is set to 0.5Q, and finally, 1Q of membrane-treated water is obtained from the membrane treatment tank 50.

[0071] In the activated sludge treatment apparatus 3 of the third embodiment, the biological treatment tank 16 further includes the anaerobic region 25, thereby enabling effective removal of phosphorus from organic wastewater containing nitrogen and phosphorus. Furthermore, activated sludge that has absorbed excess phosphorus in the aerobic region 30A is internally circulated by the internal circulation device 80, and is returned to the anaerobic region 25 via the anoxic region 20A, thereby effectively removing phosphorus from the nitrogen-containing organic wastewater. As a result, the phosphorus concentration in the treated water discharged from the membrane treatment tank 50 can be reduced.

[0072] In the activated sludge treatment device 3 of the third embodiment, which simultaneously removes nitrogen and phosphorus from organic wastewater containing nitrogen and phosphorus, the size of the external circulation device 70 can be made smaller than in the conventional case, as in the second embodiment. Furthermore, the activated sludge treatment device 3 of the third embodiment can achieve a high nitrogen removal rate while also achieving a high phosphorus removal rate compared to a single-stage system. The activated sludge treatment device 3 of the third embodiment can achieve, for example, a nitrogen removal rate of 70% or more and a phosphorus removal rate of 70%.

[0073] The third embodiment further includes a third internal circulation device 95 for internal circulation from the anoxic region 20B to the anaerobic region 25, so that the external circulation device 70 can return the activated sludge mixed water in the membrane treatment tank 50 to the second-stage anoxic region 20B of the biological treatment tank 10. This configuration eliminates the need to lengthen the transfer piping 72 of the external circulation device 70 in a multi-stage membrane bioreactor, and allows the external circulation pump 71 to have a smaller treatment capacity, making it easier to further reduce the size of the external circulation device 70. However, the external circulation device 70 of the third embodiment may be configured to return the activated sludge mixed water in the membrane treatment tank 50 to the first-stage anoxic region 20A of the biological treatment tank 10, in which case the third internal circulation device 95 need not be installed.

[0074] [Other embodiments] Other embodiments of the activated sludge treatment device and the method for modifying the activated sludge treatment device according to the present invention will be described below. Note that the configurations disclosed in the following embodiments can be applied in combination with the configurations disclosed in other embodiments, as long as no contradiction occurs.

[0075] In the above embodiment, an example has been described in which the biological treatment tank 10 and the membrane treatment tank 50 are installed at a distance from each other. However, the present invention is not limited to a configuration in which the biological treatment tank 10 and the membrane treatment tank 50 are installed at a distance from each other, and for example, the biological treatment tank 10 and the membrane treatment tank 50 may be arranged via a common partition wall.

[0076] In the above embodiment, an example has been described in which the volume of the anaerobic region 20 is larger than the volume of the aerobic region 30, and in particular, an example has been described in which the ratio of the volume of the aerobic region 30 to the volume of the anaerobic region 20 is in the range of 1:1.1 to 1.5. However, in the present invention, the size relationship and volume ratio between the volumes of the anaerobic region 20 and the aerobic region 30 are not limited. For example, the volumes of the anaerobic region 20 and the aerobic region 30 may be approximately equal, or the volume of the anaerobic region 20 may be smaller than the volume of the aerobic region 30.

[0077] In the above embodiment, the internal circulation device 80 has been described as an example of a configuration in which an air lift pump is used as the internal circulation pump 81 installed in the aerobic region 30. However, in the present invention, the types of the internal circulation pump 81, transfer piping 82, etc. that constitute the internal circulation device 80 are not limited. For example, the internal circulation pump 81 may be any of various submersible pumps, land pumps, etc. Furthermore, the types of the external circulation pump 71, transfer piping 72, etc. that constitute the external circulation device 70 are not limited. For example, the external circulation pump 71 may be any of various land pumps, submersible pumps, etc.

[0078] In the multi-stage membrane bioreactor activated sludge treatment devices (activated sludge treatment devices 2 and 3) of the second and third embodiments, the membrane treatment tank 50 has been described as being configured to perform solid-liquid separation on treated water flowing in from at least the final aerobic zone 30B. However, the treated water flowing in to the membrane treatment tank 50 of the present invention is not limited to that flowing in from the final aerobic zone 30B. For example, treated water flowing in from an intermediate aerobic zone may be subjected to solid-liquid separation in the membrane treatment tank 50.

[0079] In the second and third embodiments of the multi-stage membrane bioreactor activated sludge treatment apparatus (activated sludge treatment apparatuses 2 and 3), the internal circulation device 80 has been described as returning the activated sludge mixed water in the first-stage aerobic region 30A to the first-stage anoxic region 20A. However, in the present invention, the aerobic region 30 from which the internal circulation device 80 returns and the anoxic region 20 to which the internal circulation device 80 returns are not limited. When the biological treatment tank has multiple aerobic regions 30 and multiple anoxic regions 20, any combination of the aerobic region 30 from which the internal circulation device 80 returns and the anoxic region 20 to which the internal circulation device 80 returns can be used. For example, the internal circulation device 80 may perform the following internal circulation, and multiple internal circulation devices 80 may be provided to perform the multiple internal circulations described in (3) and (4) below. (1) A configuration in which the activated sludge mixed water in the second-stage aerobic region 30B is returned to the second-stage anaerobic region 20B (2) A configuration in which the activated sludge mixed water in the second-stage aerobic region 30B is returned to the first-stage anaerobic region 20A. (3) In addition to (1), the activated sludge mixed water in the first-stage aerobic region 30A is returned to the first-stage anaerobic region 20A. (4) In addition to (2), the activated sludge mixed water in the first-stage aerobic region 30A is returned to the first-stage anaerobic region 20A.

[0080] The same applies to the internal circulation of a three or more stage multi-step activated sludge treatment device, and in this case, the following internal circulation configuration using an internal circulation device 80 is exemplified. (i) A configuration in which the activated sludge mixed water in the aerobic region 30 is returned to the anoxic region 20 immediately preceding it. (ii) A configuration in which the activated sludge mixed water in the aerobic region 30 is returned to the anoxic region 20 in the preceding stage across one or more other aerobic regions. (iii) A configuration in which two or more of one of the configurations (i) and (ii) above are combined, or at least two of the configurations (i) and (ii) above are combined.

[0081] It is preferable that the internal circulation device 80 return the wastewater to the anoxic region 20 at the previous stage as much as possible, and it is also preferable that the second internal circulation device 90, the third internal circulation device 95, and the fourth internal circulation device 98 return the wastewater to the anoxic region 20 or anaerobic region 25 at the previous stage as much as possible.

[0082] In the above embodiment, an example was described in which the partition member 11 has an opening. However, in the present invention, it is sufficient that treated water treated in each region flows into the subsequent region through the partition member 11. A gap may be formed between the lower end of the partition member 11 and the bottom surface of the biological treatment tank 10, or the height of the upper end of the partition member 11 may be low so that treated water treated in each region overflows and flows into the subsequent region. Water may be pumped from the previous region to the subsequent region between the regions separated by the partition member 11.

[0083] In the above embodiment, the configuration in which the biological treatment tank 16 has the anaerobic region 25 in the multi-step activated sludge treatment device 3 of the third embodiment has been described. However, the configuration in which the biological treatment tank 16 has the anaerobic region 25 is not limited to the multi-step activated sludge treatment device. For example, a single-stage circulation type membrane bioreactor activated sludge treatment device such as the activated sludge treatment device 1 of the first embodiment may further have an anaerobic region partitioned by a partition member 11 in the stage preceding the anoxic region 20.

[0084] In the first embodiment, an example has been described in which the partition member relocation step is performed before the internal circulation device installation step in the method for modifying the activated sludge treatment device 1. However, in the method for modifying the activated sludge treatment device of the present invention, the order of the steps is not limited, and for example, the internal circulation device installation step may be performed before the partition member relocation step.

[0085] In the first embodiment, an example has been described in which the external circulation device 75 is replaced with a smaller one by installing a new internal circulation device 80 in a modification method for the activated sludge treatment device 1. However, the size of the external circulation device 75 does not necessarily have to be changed, and the installation of the internal circulation device 80 may increase the overall treatment capacity compared to the conventional system. In this case, it can be said that the size of the external circulation device 75 is reduced relative to the treatment capacity.

[0086] In the above embodiment, an example of a method for converting an existing activated sludge treatment device 100 into the activated sludge treatment device 1 of the first embodiment has been described. However, in the present invention, the activated sludge treatment device to be converted is not limited to a single-stage circulation type membrane bioreactor treatment device. For example, it may be converted into a multi-stage membrane bioreactor treatment device (activated sludge treatment devices 2 and 3) as in the second and third embodiments, or a multi-stage membrane bioreactor treatment device.

[0087] Regarding other configurations, it should be understood that the embodiments disclosed in this specification are illustrative in all respects and that the scope of the present invention is not limited thereby. Those skilled in the art will easily understand that appropriate modifications are possible without departing from the spirit of the present invention. Therefore, other embodiments modified without departing from the spirit of the present invention are naturally included in the scope of the present invention. [Industrial Applicability]

[0088] The present invention can be used, for example, as an activated sludge treatment device in a sewage treatment plant. [Explanation of symbols]

[0089] 1, 2, 3: Activated sludge treatment equipment 100: Activated sludge treatment equipment before modification 10: Biological treatment tank 11: Partition member 20:Anoxic region 20A, 20B: Anoxic region 30: Aerobic zone 30A, 30B: Aerobic zone 50: Membrane treatment tank 51: Membrane treatment equipment 60: Aeration device 70: External circulation device 71: External circulation pump 72: Transfer piping 80: Internal circulation device 81: Internal circulation pump (air lift pump)

Claims

1. A biological treatment tank including an anaerobic region into which nitrogen-containing organic wastewater is introduced and an aerobic region disposed downstream of the anaerobic region, wherein the anaerobic region and the aerobic region are separated by at least one partition member; A membrane treatment tank arranged downstream of the aerobic zone and having a submerged membrane separation device; an aeration device that aerates each of the aerobic region and the membrane treatment tank, An activated sludge treatment apparatus comprising: an external circulation device that returns the activated sludge mixed water in the membrane treatment tank to the anoxic region; and an internal circulation device that returns the activated sludge mixed water in the aerobic region to the anoxic region.

2. The activated sludge treatment apparatus according to claim 1 , wherein the volume of the anoxic region is larger than the volume of the aerobic region.

3. 3. The activated sludge treatment apparatus according to claim 2, wherein the ratio of the volume of the aerobic region to the volume of the anaerobic region is in the range of 1:1.1 to 1.

5.

4. The activated sludge treatment apparatus according to claim 1 , wherein the internal circulation device includes an air lift pump installed in the aerobic region.

5. 2. The activated sludge treatment apparatus according to claim 1, further comprising an anaerobic zone separated by a partition member in front of the anoxic zone.

6. In the biological treatment tank, the anoxic regions and the aerobic regions partitioned by at least three of the partition members are alternately arranged from the front stage to the rear stage, The activated sludge treatment apparatus according to claim 1 , wherein the membrane treatment tank is disposed at least after the last aerobic zone.

7. A method for modifying an activated sludge treatment apparatus comprising: a biological treatment tank including an anaerobic zone into which nitrogen-containing organic wastewater is introduced and an aerobic zone located downstream of the anaerobic zone, the anaerobic zone and the aerobic zone being separated by at least one partition member; a membrane treatment tank located downstream of the aerobic zone and having a submerged membrane separation device; an aeration device for aerating each of the aerobic zone and the membrane treatment tank; and an external circulation device for returning activated sludge mixed water in the membrane treatment tank to the anaerobic zone, A method for modifying an activated sludge treatment apparatus, comprising the step of installing an internal circulation device that returns the activated sludge mixed water in the aerobic region to the anoxic region.

8. 8. The method for modifying an activated sludge treatment apparatus according to claim 7, further comprising a partition member relocation step of removing the partition member in the biological treatment tank and relocating the partition member to a position where the volume of the anaerobic region is larger than the volume of the aerobic region.

Images