JP2004358411A - Membrane separation unit for activated sludge treatment system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane separation unit which requires only a small installation area when increasing the treatment capacity of an activated sludge treatment system, and can easily increase the capacity for solid-liquid separation of treated sludge in the system without stopping the system. <P>SOLUTION: The membrane separation unit U in place of an existing settling tank (a) is connected to a biological reaction tank 1, thereby the capacity for the solid-liquid separation of the treated sludge in the system can be increased without a repair work of the settling tank (a). The membrane separation unit U is equipped with a membrane module 2 that obtains treated water by filtering the treated sludge after biological reaction treatment in the biological reaction tank 1. While passing the treated sludge through the membrane module 2 at a relatively high speed, a part of the treated sludge is filtered to extract the treated water. Back washing operations are carried out for periodically passing washing water through membrane elements reversely to the filtration direction of the treated water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a membrane separation unit applied to a water treatment system (activated sludge treatment system) for treating sewage, industrial wastewater, or the like by a so-called activated sludge process. In particular, the present invention relates to a membrane separation unit capable of easily increasing the capacity of solid-liquid separation of treated sludge when increasing the processing capacity of a water treatment system.
[0002]
[Prior art]
BACKGROUND ART Conventionally, various types of activated sludge treatment systems for treating wastewater such as sewage and industrial wastewater have been proposed. As an example, as disclosed in Patent Literature 1 below, an anaerobic aerobic system having a denitrification tank and a nitrification tank, and performing denitrification and dephosphorization of wastewater by an anaerobic step in a denitrification tank and an aerobic step in a nitrification tank. A water treatment system using the activated sludge method is known.
[0003]
In this water treatment system, nitrogen compounds contained in the sewage are oxidized by activated sludge into nitrate nitrogen in the aerobic process, and then nitrogen gas is generated by depriving the nitrate nitrogen of oxygen in the anaerobic process. Denitrification. Further, phosphorus is once released from the activated sludge in the anaerobic step, and thereafter, the activated sludge is subjected to excessive sampling of phosphorus in the aerobic step to remove phosphorus.
[0004]
In this treatment system, the treated sludge after the influent (sewage) is purified by the biological reaction treatment with the activated sludge is discharged to the final sedimentation tank. Then, the treated water and the sludge were separated by sedimenting the solid content in the treated sludge inside the final sedimentation tank, and the treated water that became the supernatant water was discharged from the system, and settled in the final sedimentation tank. Sludge is drawn out and returned to the denitrification tank and nitrification tank.
[0005]
[Patent Document 1]
JP-A-8-1189
[Problems to be solved by the invention]
By the way, the above-described activated sludge treatment system is generally installed in a factory or a sewage treatment facility. However, when the factory scale is expanded or the sewage treatment facility is expanded, the processing capacity of the activated sludge treatment system is reduced. It is necessary to increase it.
[0007]
Usually, as means for increasing the treatment capacity of the activated sludge treatment system, it is conceivable to increase the size of the biological reaction tank (denitrification tank, nitrification tank) and the size of the final sedimentation tank accordingly.
[0008]
However, if there is a limit to the size of the final sedimentation tank due to restrictions on the site area of the factory or sewage treatment facility, even if the biological reaction tank is sufficiently large, the ability to separate solid sludge from the treated sludge Is not sufficiently obtained, and as a result, it becomes impossible to increase the processing capacity of the entire system.
[0009]
In addition, when the final sedimentation tank is enlarged, the water in the final sedimentation tank is once drained, and then the final sedimentation tank will be repaired, during which time the system must be stopped. There was a problem that the operation of the factory and the sewage treatment facility had to be stopped for a long time.
[0010]
The present invention has been made in view of such a point, and an object of the present invention is to reduce the installation area when increasing the processing capacity of an activated sludge treatment system, and to stop the system. An object of the present invention is to provide a membrane separation unit capable of easily increasing the solid-liquid separation capacity of treated sludge in the system without using the system.
[0011]
[Means for Solving the Problems]
-Summary of the invention-
In order to achieve the above object, the present invention proposes a membrane separation unit newly connected to a biological reaction tank of an existing activated sludge treatment system. In other words, by connecting the membrane separation unit to the biological reaction tank instead of the existing sedimentation tank, the capacity of the system for solid-liquid separation of the treated sludge can be increased without renovating the sedimentation tank. . Further, the membrane separation unit is provided with a membrane separator for obtaining treated water by filtering the treated sludge after the biological reaction treatment in the biological reaction tank with a membrane element, and treating the treated sludge inside the membrane element at a relatively high speed. , While filtering some of the treated sludge to extract the treated water. In addition, the washing water is periodically passed through the membrane element in a direction opposite to the filtration direction of the treated water, so that solid substances adhering to the membrane element are peeled and removed.
[0012]
-Solution-
Specifically, by newly connecting to the biological reaction tank provided in the existing activated sludge treatment system, the treated sludge after performing the biological reaction treatment in this biological reaction tank is solid-liquid separated. Assume a membrane separation unit. The membrane separation unit is provided with a membrane separator and a backwashing means. The membrane separator has a membrane separator main body that is installed outside the biological reaction tank and houses the membrane element, and the membrane separator main body has a circulation circuit that circulates sludge with the biological reaction tank. The sludge is circulated through the circulation circuit, and the sludge is filtered from the primary side to the secondary side of the membrane element to obtain treated water. The backwashing means performs a backwashing operation for removing the solid matter adhering to the primary side surface of the membrane element by passing the washing water from the secondary side to the primary side of the membrane element.
[0013]
If it becomes necessary to increase the processing capacity of an existing activated sludge treatment system equipped with a biological reaction tank and a sedimentation tank due to this specific matter, replacing the sedimentation tank with the biological reaction tank To connect the membrane separation unit according to the present solution to the biological reaction tank. That is, instead of the method of precipitating the solid content in the treated sludge in the settling tank, the method is switched to solid-liquid separation of the treated sludge by membrane filtration.
[0014]
Thereby, the treated sludge after the biological reaction treatment in the biological reaction tank circulates in the circulation circuit formed between the membrane separator main body and the biological reaction tank. In other words, the treated sludge taken out of the biological reaction tank is supplied to the membrane separator main body, and a part of the sludge is filtered, which will be described later, and then returned to the biological reaction tank. This circulation operation is repeated in the circulation circuit.
[0015]
In the main body of the membrane separator, a part of the treated sludge supplied from the biological reaction tank is filtered from the primary side to the secondary side of the membrane element, whereby a part of the treated sludge is separated into a solid and a liquid. Water is obtained. That is, treated water is sequentially obtained in the main body of the membrane separator while the circulation operation in the circulation circuit is repeated.
[0016]
As described above, on the primary side of the membrane element, treated sludge having a flow rate substantially equal to the circulation flow rate in the circulation circuit flows. Therefore, if the circulation flow rate in this circulation circuit is set relatively high, the primary Sludge (solid matter) that is going to adhere to the side surface is swept away by the circulating flow and returned to the biological reaction tank without adhering to the membrane element. For this reason, the amount of sludge (solid matter) adhering per unit time on the primary surface of the membrane element is greatly reduced as compared with a general immersion type separation membrane unit. In the immersion type separation membrane unit, since the sludge is mostly retained on the primary side of the membrane element, the sludge after the treatment water is extracted is attached to the primary side surface of the membrane element without being washed away. After the start of the filtration of the sludge, a large amount of the sludge adhered to the membrane element within a short period of time, and the filtration capacity was rapidly reduced.
[0017]
According to the configuration of the present solution, the treated water is extracted from the circulating flow, so that the situation that sludge adheres to the membrane element in a short time is unlikely to occur, and the high filtration capacity is increased. It can be maintained over time. In addition, the circulation flow velocity of the circulation circuit is specifically determined by the capacity of a circulation pump provided in the circulation circuit.
[0018]
Further, in this solution, the backwashing operation is performed, for example, every predetermined time, thereby removing and removing the solid matter adhering to the primary side surface of the membrane element. Specifically, in a state where the filtration operation of the treated sludge (filtration from the primary side to the secondary side of the membrane element) is stopped, the washing water is passed from the secondary side to the primary side, and the filtration of the membrane element is performed. The solid material adhering to the primary side is peeled off. For example, by setting the above-mentioned predetermined time so that the backwashing operation is performed before the amount of the solid attached on the primary side surface of the membrane element becomes large, the attached solid is exfoliated in a short time. The time required for the backwash operation can be shortened. For this reason, it is possible to avoid a situation where a large amount of solid matter adheres to the primary side surface of the membrane element, and it is possible to stably perform a filtration operation with a high capacity, and to improve the performance of the activated sludge treatment system. it can. As a result, compared to the immersion type separation membrane method, the amount of treated water per unit time can be significantly increased (high flux) even with a small membrane area, and high-performance water treatment is realized. can do. Further, in the case where the chemical cleaning of the membrane element is performed, the frequency of the cleaning can be reduced (for example, about once every six months), so that the operation rate of the water treatment operation (filtration operation) is improved. Therefore, high-performance water treatment can also be realized.
[0019]
As the execution timing of the backwashing operation, for example, after the filtration operation is continuously performed for 5 minutes, the backwashing for 8 seconds is performed. Further, it is preferable to use the treated water obtained in the filtration operation as the washing water used in the backwash operation. The washing water is not limited to the above treated water, but may be individual water (tap water or the like). In addition, an activator or the like may be mixed in water so that the adhered solid matter can be easily removed. However, this washing water is subjected to a biological reaction after permeating from the secondary side to the primary side of the membrane element. Since it flows into the tank, it is preferable that it does not adversely affect the biological reaction treatment.
[0020]
The following is a specific configuration of the membrane separator. That is, the membrane element is formed by molding the permeable membrane material into a cylindrical shape. Then, a large number of membrane elements are accommodated in the membrane separator body, and a sludge circulation circuit is formed between the internal space of each membrane element and the biological reaction tank. Furthermore, the sludge supplied from the biological reaction tank to each membrane element is filtered from the inside, which is the primary side of each membrane element, to the outside, which is the secondary side, to obtain treated water.
[0021]
As described above, when a permeable membrane material (eg, polyester or polystyrene) is formed into a cylindrical shape to constitute a membrane element, and a large number of membrane elements are accommodated in the membrane separator main body, the inner area of each membrane element is reduced. Can be made relatively small. This leads to a reduction in the total sludge adhesion area in each of the individual membrane elements when sludge adheres to the inner surface of the membrane element. That is, in each of the membrane elements, since the sludge adhesion area is small, the solid material can be more easily separated by the backwashing operation. For this reason, the time required for the backwashing operation is shortened, and the operation rate of the filtering operation can be improved. Also, when the treated water is sucked from the membrane element, the membrane element is formed into a cylindrical shape, so it is unlikely to be deformed by the negative suction pressure, and the shape of the internal space can be maintained, and the filtration capacity is stabilized. It becomes possible to maintain it. In other words, in the case where the internal space of the membrane element is largely secured and the filtration capacity of each membrane element is to be increased, if the membrane element is a flat plate-shaped membrane element, the membrane element is easily deformed by the suction negative pressure. However, when formed into a cylindrical shape as in the present solution, deformation due to the suction negative pressure is unlikely to occur, so that a large internal space of the membrane element can be ensured. As a result, the design of the membrane element can be freely performed. The degree (degree of freedom in designing the diameter) can be increased. Specifically, the outer diameter of the membrane element is set to about 5 to 8 mm.
[0022]
As means for ensuring a high sludge flow rate in the primary space of the membrane element, the followings are listed. In other words, a configuration is provided in which a bubble supply means for supplying a conveying force to the circulating sludge by supplying bubbles flowing along the flow direction of the circulating sludge to the primary space of the membrane element through which the circulating sludge flows.
[0023]
According to this specific matter, the bubbles supplied from the bubble supply means to the primary space of the membrane element will circulate the circulating sludge flowing in the primary space in the flow direction, and the circulating sludge will flow in the primary space. There is no stagnation. In addition, the bubbles also exert a function of suppressing the adhesion of sludge to the primary side surface of the membrane element, and further reduce the amount of attached sludge (solid matter) per unit time on the primary side surface of the membrane element. be able to. As a specific configuration, the membrane element is arranged in a vertical arrangement, and the treated sludge is caused to flow upward from the lower side of the primary space, and bubbles are supplied from the lower side of the membrane element to the primary space ( Air lift). Thereby, the buoyancy of the bubbles is given as the conveying power of the circulating sludge. As a result, the power required to circulate the circulating sludge (such as the power of a circulation pump) can be reduced, and the running cost of the system can be reduced.
[0024]
Further, in the case of this solution, it is preferable that the shape of the bubble supplied from the bubble supply means is made to substantially match the shape of the cross section orthogonal to the sludge flow direction in the primary space of the membrane element. In this case, a layer filled with sludge and a layer filled with air alternately exist in the sludge flow direction in the primary space. For this reason, the sludge is forced to be swept away by the air bubbles, and the conveying force can be reliably applied to the sludge from the air bubbles, so that an efficient sludge circulation operation can be performed.
[0025]
The following is a specific configuration of the bubble supply means. That is, an air diffusion member having a shape substantially matching the shape of the cross section orthogonal to the sludge flow direction in the membrane separator main body is provided as the bubble supply means.
[0026]
In addition, the following configuration is listed as the air diffusing member. That is, the main body of the membrane separator is a tubular body having a substantially circular cross section orthogonal to the sludge flow direction. The air diffuser is made of a disc-shaped porous body substantially matching the cross-sectional shape of the membrane separator main body.
[0027]
According to the above configuration, it is possible to supply air substantially uniformly to the internal space (primary space) of each of the many membrane elements housed inside the membrane separator main body. For this reason, the sludge flow rate in the primary space of each membrane element can be made substantially uniform, and the filtration capacity can be equalized. As a result, the filtration capacity of the entire membrane separator can be improved. it can.
[0028]
The following are listed as means for more efficiently performing the backwashing operation. In other words, the configuration is such that air supply means for temporarily passing a relatively large amount of air into the primary space of the membrane element during the backwashing operation is provided.
[0029]
As the air supply means, a compressor that generates pressurized air can be applied, but the following configuration may also be used. In other words, a storage container for storing air is provided, and during execution of the backwashing operation, the internal space of the storage container is released to the primary space of the membrane element to allow a relatively large amount of air to pass through the primary space of the membrane element. Configuration. According to this configuration, for example, when the bubble supply unit is provided, a part of the bubbles supplied from the bubble supply unit is stored in the storage container. Can supply a large amount of air to the primary space of the membrane element. In other words, in this case, the air bubbles supplied from the air bubble supply means can be used as air for the backwash operation, and a special air pressure feeding mechanism is not required, and the system configuration can be simplified.
[0030]
Next, a solution in a case where the membrane separator is washed with a chemical solution will be described. First, a chemical solution supply pipe for supplying a chemical solution to the inside of the membrane separator main body at the time of cleaning the chemical solution of the membrane separator main body is connected to an outlet pipe for drawing out treated water from the membrane separator main body. Further, there is provided a chemical cleaning means for performing a chemical cleaning operation of supplying a chemical from the chemical supply pipe through the outlet pipe to the inside of the membrane separator main body. Specifically, the chemical cleaning means is configured to execute the chemical cleaning operation at predetermined time intervals.
[0031]
According to this specific matter, at the time of cleaning the chemical, the chemical supplied from the chemical supply pipe to the inside of the membrane separator via the outlet pipe flows from the secondary side of the membrane element toward the primary side. This is the same flow as in the case of the backwashing described above. As a result, the solid matter adhering to the primary side surface of the membrane element is easily peeled off and dissolved, and the membrane element is purified, so that efficient chemical cleaning can be performed. This makes it possible to reduce the time required for the chemical liquid cleaning operation, and to quickly return the membrane separator to improve the operation rate of the filtration operation. In addition, if chemical cleaning is performed while the sludge circulation in the circulation circuit is stopped, the amount of chemical used for chemical cleaning only needs to be about the volume in the main body of the membrane separator. The amount of used chemical liquid can be reduced as compared with the case of cleaning the liquid. Thereby, the amount of waste liquid after the chemical solution cleaning is reduced, and the treatment can be easily performed.
[0032]
Further, the membrane separator main body is provided with a discharge means for discharging and removing the chemical solution in the membrane separator main body after the chemical solution cleaning is completed. According to this, after the chemical solution washing is completed, most of the chemical solution in the membrane separator main body is discharged and removed by the discharge means, and the chemical solution does not flow into the biological reaction tank. In the conventional immersion type separation membrane unit, when the membrane element is washed with a chemical solution, the chemical solution is present in the biological reaction tank as it is, and the sludge activity is reduced, which adversely affects the subsequent biological reaction treatment. Was exerted. In the present solution, since such a situation does not occur, the biological reaction treatment can always be stably performed, and the high performance of the activated sludge treatment system can be maintained.
[0033]
Further, the membrane separation unit includes an introduction pipe for introducing the treated sludge after the biological reaction treatment in the biological reaction tank into the membrane separation unit. The introduction pipe is provided with a withdrawing means for extracting excess sludge in the treated sludge taken out of the biological reaction tank from the circulation circuit. According to this configuration, a configuration for pulling out excess sludge can be easily realized, and the practicality of the activated sludge treatment system can be improved.
[0034]
Next, a case where the present invention is applied to a processing system in which a plurality of membrane separators are connected in parallel to a biological reaction tank will be described. First, a plurality of membrane separators are connected to a biological reaction tank in parallel. Further, the backflow cleaning means is configured to execute the backflow cleaning operation on only one selected from the plurality of membrane separators at the time of backflow cleaning. According to this configuration, only one of the plurality of membrane separators performs the backwashing operation, and the other membrane separators perform the filtration operation of the circulating sludge. For this reason, it is possible to maintain the high performance of the membrane element by the backwashing operation without greatly reducing the filtration capacity of the entire system.
[0035]
Further, a plurality of membrane separators are connected to the biological reaction tank in parallel with each other, and the chemical cleaning means performs a chemical cleaning operation on only one selected from the plurality of membrane separators at the time of chemical cleaning. It is configured to execute. Also in this case, only one of the plurality of membrane separators performs the chemical cleaning operation, and the other membrane separators perform the filtration operation of the circulating sludge. For this reason, it is possible to maintain the high performance of the membrane element by the above-mentioned chemical cleaning operation without greatly reducing the filtration capacity of the entire system.
[0036]
In addition, when the present invention is applied to an activated sludge treatment system using an anaerobic and aerobic activated sludge method in a case where the bubble supply means is provided as described above, the following configuration is cited. That is, an anaerobic tank and an aerobic tank are provided as biological reaction tanks. A sludge return pipe for returning the circulated sludge from the membrane separator main body to the biological reaction tank is branched corresponding to the anaerobic tank and the aerobic tank, respectively, while a return for adjusting the amount of sludge returned to the anaerobic tank and the aerobic tank. A quantity adjusting means (for example, a three-way valve) is provided.
[0037]
According to this configuration, the sludge supplied from the aerobic tank to the membrane separator main body can be returned to the anaerobic tank by the sludge return pipe. In the conventional activated sludge treatment system using the conventional anaerobic-aerobic activated sludge method, it is necessary to provide a special return pipe for returning sludge from the aerobic tank to the anaerobic tank, and to provide a pump in the return pipe. According to this solution, the circulation circuit has the functions of the return pipe and the pump. Therefore, the sludge can be returned from the aerobic tank to the anaerobic tank by effectively utilizing the circulation circuit, and the conventional return pipe and pump are not required, and the entire system can be made compact.
[0038]
When the bubble supply means is provided as described above, air (oxygen) is supplied to the treated sludge flowing through the membrane separator main body. For this reason, when the amount of air (DO (Dissolved Oxygen): dissolved oxygen amount) required for the aerobic tank is supplied to the treated sludge by the bubble supply means, and the treated sludge is returned to the aerobic tank, it is preferable. An aeration device is not required for the air tank. As a result, the system configuration can be simplified.
[0039]
Further, aeration means (aeration device) for supplying air into the aerobic tank is provided, and the supply amount of air supplied from the aeration means into the aerobic tank is determined by the air supply amount from the bubble supply means and the membrane separation. An aeration amount adjusting means for adjusting the amount of circulated sludge returned from the vessel body into the aerobic tank is provided. In this case, of the amount of air required for the aerobic tank, how much air is supplied by the air from the bubble supply means is determined by the amount of air supplied from the bubble supply means and from the membrane separator body into the aerobic tank. The amount of circulation sludge should be recognized and only the shortage should be supplied from the aeration means into the aerobic tank. As a result, more air than necessary is not supplied into the aerobic tank, and the running rate of the system can be significantly reduced by minimizing the operation rate of the aeration means.
[0040]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where the present invention is applied to a water treatment system using an anaerobic aerobic activated sludge method will be described. In addition, in order to facilitate understanding of the present invention, first, in the first embodiment, a water treatment system provided with only one membrane module as a membrane separator will be described. A water treatment system including a plurality of the membrane modules will be described in a second embodiment.
[0041]
(1st Embodiment)
FIG. 1 is a conceptual diagram showing a case where the membrane separation unit U according to the present embodiment is applied in place of the existing settling tank a when increasing the processing capacity of an existing activated sludge treatment system. That is, it is a diagram showing a case where the membrane separation unit U is newly connected to the biological reaction tank 1 of the existing activated sludge treatment system. In this case, the biological reaction tank 1 is changed to a large one in order to increase the processing capacity in the biological reaction tank 1.
[0042]
Before describing the configuration and the sewage treatment operation when the membrane separation unit U according to the present embodiment is applied, a schematic configuration of an existing activated sludge treatment system will be described.
[0043]
In this existing activated sludge treatment system, the biological reaction tank 1 and the sedimentation tank a are connected by a discharge pipe b, and the treated sludge after the biological reaction treatment in the biological reaction tank 1 is taken out from the discharge pipe b and settled. a. In the sedimentation tank a, the treated water and the sludge are separated by sedimenting solids in the treated sludge, and the treated water that has become supernatant water is discharged to the treated water tank 3. On the other hand, the sludge settled in the settling tank a is drawn out by the drawing pipe c provided with the pump d and returned to the biological reaction tank 1. Moreover, the biological reaction tank 1 includes an aerobic tank 12 and an anaerobic tank 11, and the two tanks 11 and 12 are connected by a return pipe e for returning sludge from the aerobic tank 12 to the anaerobic tank 11. The return pipe e is provided with a pump f.
[0044]
When the membrane separation unit U according to the present embodiment is applied instead of the existing sedimentation tank a, first, a sludge take-out pipe 51 and a sludge return pipe 52 extending from the membrane module 2 provided in the membrane separation unit U are used. Is connected to the biological reaction tank 1. Specifically, the upstream open end of the sludge removal pipe 51 is immersed in the water in the biological reaction tank 1, while the downstream open end of the sludge return pipe 52 is positioned above the biological reaction tank 1. Details of these pipes will be described later.
[0045]
Further, the treated water take-out pipe 53 and the backwashing pipe 54 extending from the membrane module 2 are connected to the treated water tank 3. Specifically, the downstream open end of the treated water take-out pipe 53 is positioned above the treated water tank 3, while the upstream end of the backwashing pipe 54 is connected to the treated water tank 3. Details of these pipes will also be described later.
[0046]
As described above, even while the pipes 51, 52, 53, and 54 of the membrane separation unit U are connected to the biological reaction tank 1 and the treatment water tank 3, the treatment by the biological reaction tank 1 and the sedimentation tank a is performed. Since the operation can be performed, the sewage treatment operation is continuously performed. In addition, it may be temporarily stopped as needed.
[0047]
Then, after the connection operation of the membrane separation unit U is completed, the introduction of the treated sludge from the biological reaction tank 1 to the settling tank a is stopped, and at the same time, the circulation pump P1 provided in the sludge removal pipe 51 is started. . Thereby, the treated sludge in the biological reaction tank 1 is introduced into the membrane module 2 from the sludge removal pipe 51, and solid-liquid separation by the membrane module 2 is started. The details of the solid-liquid separation operation will also be described later.
[0048]
By such an operation, since the solid-liquid separation method using the precipitation tank a is switched to the solid-liquid separation method using membrane filtration, the operation can be started immediately after the membrane separation unit U is connected, and the biological reaction tank 1 can be started. There is no need to remove the water inside, and there is no need to temporarily stop the water treatment system.
[0049]
FIG. 2 is a schematic configuration diagram illustrating a state where the membrane separation unit U is connected to the biological reaction tank 1. When the membrane separation unit U is connected to the biological reaction tank 1 in this way, the existing sedimentation tank a becomes unnecessary, and thereafter, the sedimentation tank a is removed. In addition, the outlet pipe b, the extraction pipe c, the return pipe e, and the pumps d and f provided therein are also unnecessary, so that these are also removed. The reason why these can be removed will be described later. Hereinafter, a configuration of a water treatment system to which the present membrane separation unit U is applied and a sewage treatment operation will be described.
[0050]
-Description of the schematic configuration of the water treatment system-
FIG. 2 is a diagram showing a schematic configuration of a water treatment system to which the membrane separation unit U according to the present embodiment is applied. As shown in FIGS. 1 and 2, the membrane separation unit U includes a membrane module 2, a chemical solution tank 4, and various pipes, and these devices are housed in one package to be a unit. Alternatively, each of these devices is installed on the same base plate to form a unit.
[0051]
As described above, the existing activated sludge treatment system includes the denitrification tank 11 as the anaerobic tank and the nitrification tank 12 as the aerobic tank that constitute the biological reaction tank 1, and the treatment water tank 3. In the present water treatment system (water treatment system to which the membrane separation unit U is applied), the biological reaction tank 1 and the nitrification tank 12 are used as they are.
[0052]
The denitrification tank 11 is for introducing inflow water (dirty water) that has passed through the fine mesh screen 13 provided on the upstream side. A stirrer 14 is installed inside the denitrification tank 11, and the sewage in the denitrification tank 11 is stirred by the driving of the stirrer 14, so that the anaerobic process is performed.
[0053]
On the other hand, the sewage treated in the denitrification tank 11 flows into the nitrification tank 12. Further, an air supply pipe 61 extending from an aeration blower B1 as an aeration means is introduced into the nitrification tank 12, and air can be supplied from a diffuser 61a provided at the tip of the air supply pipe 61. I have. Then, air is supplied into the nitrification tank 12 in accordance with the driving of the aeration blower B1, and the processing in the aerobic step accompanying the air is supplied.
[0054]
Hereinafter, the principle of the biological reaction treatment (aerobic step and anaerobic step) performed in the denitrification tank 11 and the nitrification tank 12 will be described. First, the nitrogen compound contained in the sewage is oxidized by activated sludge into nitrate nitrogen in the aerobic step in the nitrification tank 12, and then deprives the nitrate nitrogen of oxygen in the anaerobic step in the denitrification tank 11 to obtain nitrogen gas. Is generated, thereby performing denitrification (the operation of returning sludge from the nitrification tank 12 to the denitrification tank 11 at this time will be described later). Further, in the anaerobic process, phosphorus is once released from the activated sludge, and thereafter, the activated sludge is subjected to excessive sampling of phosphorus in the aerobic process to perform phosphorus removal. Such treatment is performed in the biological reaction tank 1 to perform denitrification and phosphorus removal.
[0055]
The treated water tank 3 collects the treated water extracted by sludge solid separation by the membrane module 2 described later. In the treated water tank 3, chlorination and the like are performed on the treated water, and the treated water after the disinfection is discharged as effluent water.
[0056]
The chemical liquid tank 4 which is a constituent member of the membrane separation unit U stores a chemical for cleaning the membrane module 2 described below with a chemical liquid. That is, at the time of the chemical cleaning performed every predetermined period, the chemical stored in the chemical tank 4 is supplied to the membrane module 2. The piping structure for this chemical cleaning and the chemical cleaning operation will be described later.
[0057]
-Description of membrane module 2-
Next, a description will be given of the membrane module 2 which is a device which is a feature of the present embodiment. 3 is a cross-sectional view showing the internal structure of the membrane module 2, and FIG. 4 is a cross-sectional view showing a part of a state where the membrane elements 22, 22,.
[0058]
The membrane module 2 is provided with a main body casing 21 as a substantially cylindrical membrane separator main body which is installed vertically, and a large number of membrane elements 22, 22,... Are accommodated in the main body casing 21. Has become. More specifically, as shown in FIG. 3, the main body casing 21 is configured as an element accommodating portion 23 having a constant inner diameter at a central portion in the longitudinal direction. 615) are accommodated in a bundled state. The treatment capacity of the membrane module 2 is determined by its outer diameter, length (height), and the number of membrane elements 22, 22,... The choice will depend on how much processing power is to be increased.
[0059]
Each of the membrane elements 22, 22,... Is a so-called straw-shaped member having a small diameter (for example, 5.2 mm in outer diameter) in which a permeable membrane material is formed into a cylindrical shape, and when sludge flows into the inside thereof, It is constituted by a microporous membrane or the like so that only water can be filtered out from the sludge. In addition, polyester, polystyrene, polyvinyl chloride, and the like are listed as a permeable membrane material constituting the membrane element 22. The permeable membrane material is not limited to these materials.
[0060]
Thus, a sludge inflow space 24 is formed in a lower portion of the main body casing 21 in the longitudinal direction, and a sludge outflow space 25 is formed in an upper portion of the main body casing 21 in the longitudinal direction. Also, at both ends in the longitudinal direction of the membrane elements 22, 22,... (Regions close to the sludge inflow space 24 and the sludge outflow space 25), the outer peripheral surfaces of these membrane elements 22, 22,. Are filled with resin, whereby the internal space of each of the membrane elements 22, 22,... Is in communication with the sludge inflow space 24 and the sludge outflow space 25, and each of the membrane elements 22, 22, ,... Are not in communication with the sludge inflow space 24 and the sludge outflow space 25.
[0061]
A discharge pipe 64 is connected to the bottom of the main casing 21 of the membrane module 2 as a discharge means for discharging a chemical from the bottom of the main casing 21 after a chemical cleaning operation described later is completed. The discharge pipe 64 is provided with a valve V2 which can be opened and closed freely. That is, when the valve V2 is opened after the end of the chemical cleaning operation, the chemical is discharged from the main casing 21 and does not flow into the biological reaction tank 1.
[0062]
-Explanation of circulation circuit-
The membrane module 2 and the biological reaction tank 1 are connected to each other by a sludge removal pipe 51 and a sludge return pipe 52, and the membrane module 2 and the biological reaction tank 1 are driven by a circulation pump P <b> 1 provided in the sludge removal pipe 51. Sludge is circulated between the tank 1 and the tank 1. That is, the biological reaction tank 1, the membrane module 2, the sludge removal pipe 51, and the sludge return pipe 52 constitute a sludge circulation circuit.
[0063]
One end (upstream end) of the sludge removal pipe 51 is open inside the nitrification tank 12, and the other end (downstream end) is connected to the sludge inflow space 24 of the membrane module 2. On the other hand, one end (upstream end) of the sludge return pipe 52 is connected to the sludge outflow space 25 of the membrane module 2. The other end (downstream end) of the sludge return pipe 52 is branched, one branch pipe 52a is connected to the nitrification tank 12, and the other branch pipe 52b is connected to the denitrification tank 11. That is, the sludge flowing out of the membrane module 2 is selectively returned to the nitrification tank 12 and the denitrification tank 11 by the branch pipes 52a and 52b. A three-way valve V1 is provided at a branch portion of each of the branch pipes 52a and 52b. The amount of sludge returned to the nitrification tank 12 and the denitrification tank 11 can be arbitrarily set by adjusting the opening of the three-way valve V1. It is possible.
[0064]
As described above, the sludge circulation circuit is configured by the biological reaction tank 1, the membrane module 2, the sludge removal pipe 51, and the sludge return pipe 52. It is taken out of the tank 1 and supplied to the membrane module 2. Inside the membrane module 2, a flow is generated from the sludge inflow space 24 to the sludge outflow space 25 via the internal space of each of the membrane elements 22, 22,. For this reason, as shown in FIG. 5A, a part of the sludge flowing in the internal space of each of the membrane elements 22, 22,... Is filtered, and a part of the treated sludge is separated into a solid and a liquid. The treated water is extracted outside the membrane element 22. In this way, the treated water is continuously obtained in the membrane module 2 while the sludge circulation operation in the circulation circuit is repeated. In the normal operation state, the ratio between the amount of sludge circulated in the circulation circuit and the amount of treated water extracted by the membrane element 22 is set to be about "20: 1". The present invention is not limited to this ratio.
[0065]
The sludge that has been separated into solid and liquid in the internal space of the membrane element 22 is nitrified from the internal space of the membrane element 22 through the sludge outflow space 25 and the sludge return pipe 52 along the sludge flow generated in the internal space. The tank is returned to the tank 12 or the denitrification tank 11.
[0066]
As described above, in the internal space (primary side) of the membrane element 22, the treated sludge having a flow rate substantially equal to the circulation flow rate in the circulation circuit flows. Therefore, if the circulation flow rate in this circulation circuit is set relatively high. The sludge (solid matter) to be attached to the inner surface of the membrane element 22 is washed away by the circulation flow and returned to the biological reaction tank 1 without attaching to the membrane element 22. For this reason, the amount of sludge (solid matter) adhered per unit time on the inner surface of the membrane element 22 is significantly reduced as compared with the conventional immersion type separation membrane unit. This makes it possible to maintain a high filtration capacity for a long time. FIG. 5B shows a state in which the circulating operation in the circulating circuit is continuously performed for a predetermined period of time, and the solid matter slightly adheres to the inner surface of the membrane element 22.
[0067]
-Removal of treated water-
The membrane module 2 and the treated water tank 3 are connected by a treated water take-out pipe 53 as an outlet pipe. The treated water outlet pipe 53 is branched at the side connected to the membrane module 2, and one of the branched pipes 53 a is connected to a lower portion of the element housing portion 23, and the other is connected to an upper portion of the element housing portion 23. Have been. Further, the treated water take-out pipe 53 is provided with a membrane filtration pump P2. With the driving of the membrane filtration pump P2, the treated water filtered by each of the membrane elements 22, 22,. The treated water is extracted from the treated water tank 53 through the treated water take-out pipe 53.
[0068]
−Air lift−
Further, the present system is provided with an air lift blower B2 for continuously supplying air bubbles to the internal space of each of the membrane elements 22, 22,. The air lift blower B2 and the sludge inflow space 24 of the membrane module 2 are connected by a lift air supply pipe 62. With the driving of the air lift blower B2, air is supplied to the sludge inflow space 24, and the air becomes bubbles. Are continuously supplied to the internal spaces of the membrane elements 22, 22,... (See FIGS. 5A and 5B). Specifically, a diffuser pipe 62a having a large number of openings is attached to the tip of the lift air supply pipe 62, and air bubbles are supplied to the sludge inflow space 24 from each of the openings of the diffuser pipe 62a. By the buoyancy, it is continuously supplied to the internal space of each of the membrane elements 22, 22,. In this way, the lift air supply pipe 62 and the air lift blower B2 constitute the bubble supply means according to the present invention.
[0069]
As described above, air bubbles are continuously supplied to the internal space of each of the membrane elements 22, 22,..., So that the air bubbles push sludge in the membrane element 22 in the flow direction (upward). In addition, sludge does not stay in the internal space of the membrane element 22. In addition, the bubbles also exert a function of suppressing the adhesion of sludge to the inner surface of the membrane element 22, and further reduce the amount of sludge (solid matter) adhered to the inner surface of the membrane element 22 per unit time. be able to. As a result, the buoyancy of the bubbles is given as the conveying force of the circulating sludge, and as a result, the power required to circulate the circulating sludge (the power of the circulating pump P1) can be reduced, and the running of the system can be reduced. Cost can be reduced.
[0070]
In this case, the outer diameter of the bubbles supplied to the internal space of the membrane element 22 is set to be substantially equal to the inner diameter of the membrane element 22 or slightly larger than the inner diameter of the membrane element 22. According to this, a layer filled with sludge and a layer filled with air alternately exist in the internal space of the membrane element 22 in the sludge flow direction (FIGS. 5A and 5B). ), The sludge is forced to be washed away by the bubbles, and the conveying force can be reliably applied to the sludge from the bubbles, so that an efficient sludge circulation operation can be performed.
[0071]
-Backwashing-
The treated water tank 3 and the treated water take-out pipe 53 are connected by a backwashing pipe 54. The backwashing pipe 54 is provided with a backwashing pump P3. When the backwashing pump P3 is driven, the treated water in the treated water tank 3 passes through the backwashing pipe 54 and the treated water take-out pipe 53 to form a membrane module. 2 (see arrows indicated by broken lines in FIG. 2).
[0072]
That is, the backwashing operation is performed by driving the backwashing pump P3 at predetermined time intervals, whereby the solid matter adhering to the inner surfaces of the membrane elements 22, 22,. . When the backwashing operation is performed, the driving of the circulation pump P1 is continued, while the membrane filtration pump P2 is stopped to stop the filtration operation. As described above, the backwashing means in the present invention is constituted by the backwashing pipe 54 and the backwashing pump P3.
[0073]
By performing such a backwashing operation, as shown in FIG. 5 (c), it is possible to easily peel off and remove the solid matter adhering to the inner surface of the membrane element 22, and to achieve high performance. Can be stably performed, and the performance of the activated sludge treatment system can be improved. As a result, the amount of treated water obtained per unit time can be significantly increased (increased flux) even with a small membrane area as compared with the conventional one, without increasing the size of the entire system. , High-performance water treatment can be realized. Specifically, the processing capacity of the conventional immersion type separation membrane unit was about 0.4 m ³ / m ² · day, but the processing capacity of the membrane module 2 according to the present embodiment was 0.8 m ^3. It has been confirmed by experiments that the ratio is improved to about / m ² · day.
[0074]
In addition, according to the present embodiment, the frequency of chemical solution cleaning for the membrane element 22 can be reduced (for example, about once every six months), so that the operation rate of the water treatment operation (filtration operation) is improved. Thus, high-performance water treatment can be realized.
[0075]
−Air injection−
In order to perform the above-mentioned backwashing operation more efficiently, the present system is provided with an air injection compressor C for temporarily passing a relatively large amount of air into the internal space of each of the membrane elements 22, 22,. The air injection compressor C and the sludge take-out pipe 51 are connected by an air injection pipe 63. With the driving of the air injection compressor C, pressurized air flows through the sludge take-out pipe 51 and the sludge inflow space 24. Are temporarily supplied in large quantities to the internal spaces of the membrane elements 22, 22,.... As described above, the air injection means according to the present invention is constituted by the air injection pipe 63 and the air injection compressor C.
[0076]
By this pressurized air, the sludge adhering to the inner surface of the membrane element 22 can be quickly removed (see FIG. 5C), and the time required for the backwashing operation is reduced, and the filtration operation is reduced. The operation rate can be improved.
[0077]
-Chemical cleaning-
The chemical liquid tank 4 and the treated water take-out pipe 53 are connected by a chemical liquid supply pipe 55. The chemical supply pipe 55 is provided with a chemical cleaning pump P4. With the driving of the chemical cleaning pump P4, the chemical in the chemical tank 4 is passed through the chemical supply pipe 55 and the treated water extraction pipe 53, and the membrane module 2 is discharged. (See an arrow indicated by a chain line in FIG. 2).
[0078]
In other words, the chemical cleaning operation is performed by driving the chemical cleaning pump P4 every predetermined period, whereby the solid substances adhering to the inner surfaces of the respective membrane elements 22, 22,... Can be dissolved and removed. . When the chemical cleaning operation is performed, all of the pumps P1 to P3 except the chemical cleaning pump P4 are stopped, and the filtering operation and the air supply operation are stopped. The execution of the chemical cleaning operation by the drive control of the pump is performed by the control of a chemical cleaning means provided in a controller (not shown).
[0079]
By performing such a chemical cleaning operation at predetermined intervals, solid substances adhering to the inner surface of the membrane element 22 are easily separated and dissolved, and the membrane element 22 is purified. Good chemical cleaning can be performed. This makes it possible to reduce the time required for the chemical liquid cleaning operation, and to quickly return the membrane module 2 to improve the operation rate of the filtration operation. In addition, since the amount of the chemical used for cleaning the chemical is only required to be about the volume in the main body casing 21 of the membrane module 2, the amount of the chemical used can be reduced as compared with the conventional case of cleaning the immersion type separation membrane unit with the chemical. Thereby, the amount of waste liquid after the chemical solution cleaning is reduced, and the treatment can be easily performed. In addition, since the chemical does not flow into the biological reaction tank, the activity of the activated sludge in the biological reaction tank is not reduced, and stable treatment can be performed even after the chemical treatment.
[0080]
-Execution timing of each operation-
Next, the execution timing of the above-described backwashing operation and chemical solution cleaning operation will be described. FIG. 6 is a timing chart showing the operation of the present water treatment system. As shown in this figure, in the normal treated water filtration operation, the membrane filtration pump P2, the circulation pump P1, and the air lift blower B2 are operated, and the treated water filtration operation associated with the above-described sludge circulation operation is performed. Then, the treated water is continuously drawn into the treated water tank 3.
[0081]
Then, after this operation is performed for a predetermined time A (for example, 5 minutes), the operation is switched to the backwashing operation. As described above, the backwashing operation is performed by stopping the membrane filtration pump P2 and driving the backwashing pump P3. This backwashing operation is performed only for a time B (for example, 8 seconds) in the figure. During the backwashing operation, the air injection compressor C is temporarily driven, and a large amount of pressurized air is temporarily supplied to the internal space of each of the membrane elements 22, 22,. The drive timing of the air injection compressor C is set to an intermediate time among the execution times of the backwashing operation.
[0082]
After such a backwashing operation is performed, the activation of the membrane filtration pump P2 is inhibited for a predetermined time (time E in FIG. 6), and after the elapse of the wait time, the membrane filtration pump P2 is activated. Thus, the process water filtration operation associated with the above-described circulation operation is restored. The above operation is repeated.
[0083]
The chemical cleaning operation is performed every six months. In this case, as described above, all the pumps P1 to P3 except the chemical cleaning pump P4 are stopped.
[0084]
-Effects of Embodiment-
As described above, in the present embodiment, while the treated sludge is passed through the inside of the membrane element 22 at a relatively high speed, a part of the treated sludge is filtered to extract the treated water. At this time, the sludge (solid matter) to be attached to the inner surface of the membrane element 22 is washed away by the circulating flow and returned to the biological reaction tank 1 without attaching to the membrane element 22. For this reason, the amount of sludge adhering per unit time on the inner surface of the membrane element 22 is greatly reduced as compared with the conventional immersion type separation membrane unit. Therefore, it is possible to maintain a high filtering ability for a long time. Further, in this embodiment, the solid matter adhering to the inner surface of the membrane element 22 is peeled and removed by periodically passing the washing water through the membrane element 22 in a direction opposite to the filtration direction of the treated water. I have to. For this reason, a situation where a large amount of solid matter adheres to the inner surface of the membrane element 22 can be avoided, and a high-performance filtration operation can be stably performed, and the activated sludge treatment system can be improved in performance. it can. As a result, the amount of treated water obtained per unit time can be significantly increased (increased flux) even with a small membrane area as compared with the conventional one, without increasing the size of the entire system. , High-performance water treatment can be realized. Further, since the frequency of cleaning the membrane element 22 with the chemical solution can be reduced, the operation rate of the water treatment operation (filtration operation) can be improved, thereby also realizing high-performance water treatment. .
[0085]
Until now, when increasing the treatment capacity of a water treatment system, a immersion-type separation membrane unit was installed in a biological reaction tank to increase the concentration of MLSS (Mixed Liquid Suspended Solids). However, in this method, when the immersion-type separation membrane unit is installed, water in the biological reaction tank is once extracted, and the immersion-type separation membrane unit is fixed to the bottom of the biological reaction tank with an anchor or the like, and then, the biological reaction is performed again. It was necessary to supply water into the tank and then start operation. When the membrane separation unit U of the present embodiment is used, it is possible to start the operation immediately after connecting the sludge take-out pipe 51 and the sludge return pipe 52 of the membrane separation unit U to the biological reaction tank 1. Therefore, there is no need to remove the water from the biological reaction tank, and there is no need to temporarily stop the water treatment system. For this reason, an easy and highly practical membrane separation unit U can be provided.
[0086]
Further, in the present embodiment, as described above, the sludge return pipe 52 for returning the circulating sludge from the main body casing 21 of the membrane module 2 to the biological reaction tank 1 is branched corresponding to the denitrification tank 11 and the nitrification tank 12, respectively. A three-way valve V1 is provided as return amount adjusting means capable of adjusting the amount of sludge returned to the denitrification tank 11 and the nitrification tank 12. Therefore, the sludge supplied to the main casing 21 can be returned to the denitrification tank 11 by the sludge return pipe 52. In the conventional activated sludge treatment system using the anaerobic-aerobic activated sludge method, a special return pipe (return pipe e in FIG. 1) for returning sludge from the aerobic tank to the anaerobic tank is provided. It was necessary to provide a pump f. According to the present embodiment, the functions of the return pipe e and the pump f are provided in the circulation circuit. Therefore, the sludge can be returned from the nitrification tank 12 to the denitrification tank 11 by effectively utilizing the circulation circuit, and the conventional return pipe e and pump f are not required, and the entire system can be made compact. . In the normal operation state, the amount of sludge returned from the membrane module 2 to the nitrification tank 12 and the amount of sludge returned to the denitrification tank 11 are adjusted to “3: 1”. The present invention is not limited to this ratio.
[0087]
Further, the supply amount of air supplied from the aeration blower B1 to the nitrification tank 12 is adjusted according to the air supply amount from the air lift blower B2 and the return amount of the circulating sludge from the sludge return pipe 52 into the nitrification tank 12. If the aeration blower B1 is controlled such that the sum of the amount of oxygen in the sludge returned into the nitrification tank 12 and the amount of oxygen from the aeration blower B1 becomes the target DO, air in the nitrification tank 12 becomes more than necessary. The supply of the aeration blower B1 is eliminated, and the operating rate of the aeration blower B1 is reduced to a necessary minimum, so that the running cost of the system can be significantly reduced. The adjustment of the supply amount of air supplied from the aeration blower B1 to the nitrification tank 12 is performed under the control of an aeration amount adjusting means provided in a controller (not shown). In the normal operation state, the supply amount of air from the aeration blower B1 and the supply amount of air from the air lift blower B2 are adjusted to "3: 1". The present invention is not limited to this ratio.
[0088]
In this embodiment, the aeration blower B1 for supplying air to the nitrification tank 12 is provided. However, the amount of air required for the nitrification tank 12 is given to the treated sludge by the air lift blower B2, and the treated sludge is nitrified. When returning to the tank 12, the aeration blower B1 becomes unnecessary. As a result, the system configuration can be simplified.
[0089]
(First Modification)
Next, a first modification of the above-described first embodiment will be described. This example is a modification of the configuration for temporarily passing a relatively large amount of air through the internal space of each of the membrane elements 22, 22,. Other configurations are the same as those of the above-described first embodiment, and therefore, only the differences from the first embodiment will be described here.
[0090]
FIG. 7 is a diagram illustrating a schematic configuration of a water treatment system according to the present example. As shown in FIG. 7, in the water treatment system according to the present embodiment, the downstream side of the lift air supply pipe 62 connected to the air lift blower B2 is branched, and one branch pipe 62b is connected to the sludge inflow space 24 of the membrane module 2. And the other branch pipe 62c is connected to the sludge removal pipe 51. Further, a storage container 65 for temporarily storing air supplied from the air lift blower B2 is provided in the middle of the other branch pipe 62c. Opening / closing valves V3 and V4 are provided on the upstream and downstream pipes of the storage container 65, respectively.
[0091]
Therefore, at the time of the treated water filtration operation, only the upstream opening / closing valve V3 is opened while the air lift blower B2 is driven, and a part of the air supplied from the air lift blower B2 flows into the branch pipe 62c and flows into the storage container 65. It is stored inside.
[0092]
During the backwashing operation, the on-off valve V3 on the upstream side is closed and the on-off valve V4 on the downstream side is opened, so that the air stored in the storage container 65 is discharged into the sludge take-out pipe 51, the sludge Are temporarily supplied in large quantities to the internal space of each of the membrane elements 22, 22,... Via the inflow space 24. Thereby, solid matter adhering to the inner surface of the membrane element 22 can be effectively peeled and removed.
[0093]
That is, in this example, by using the air bubbles supplied from the air lift blower B2 as air for the backflow cleaning operation, the air injection compressor C and the air injection pipe 63 in the first embodiment can be eliminated, The system configuration can be simplified.
[0094]
(Second Modification)
Next, a second modification of the above-described first embodiment will be described. This example is a modification of the configuration for continuously supplying air bubbles from the air lift blower B2 to the internal spaces of the respective membrane elements 22, 22,. Other configurations are the same as those of the above-described first embodiment, and therefore, only the differences from the first embodiment will be described here.
[0095]
FIG. 8 is a cross-sectional view illustrating the internal structure of the membrane module 2 according to the present example. FIG. 9 is a perspective view of the air diffusing member 62d attached to the tip of the lift air supply pipe 62. As shown in these figures, a diffuser member 62d composed of a disc-shaped porous body substantially matching the cross-sectional shape of the main body casing 21 of the membrane module 2 is attached to the tip of the lift air supply pipe 62. A diffuser member 62 d is provided at the bottom of the sludge inflow space 24.
[0096]
For this reason, it is possible to supply air substantially uniformly to the internal space (primary space) of each of the large number of membrane elements 22, 22, ... housed in the main body casing 21 of the membrane module 2. Become. Therefore, the sludge flow rate in the internal space of each of the membrane elements 22, 22,... Can be made substantially uniform, and the filtration capacity can be equalized. As a result, the filtration capacity of the entire membrane separation device can be improved. Can be planned.
[0097]
(2nd Embodiment)
Next, a second embodiment of the present invention will be described. This embodiment relates to a water treatment system provided with a plurality of membrane modules. Here, a water treatment system including five membrane modules will be described. Further, since the configuration of each membrane module is the same as that of the first embodiment described above, description thereof will be omitted.
[0098]
FIG. 10 is a piping diagram of the water treatment system according to the present embodiment. As shown in this figure, each of the membrane modules 2A to 2E is connected in parallel to the biological reaction tank 1, the treatment water tank 3, and the chemical tank 4. That is, the sludge take-out pipe 51, the sludge return pipe 52, the treated water take-out pipe 53, the backwashing pipe 54, and the chemical supply pipe 55 are branched so as to correspond to the respective membrane modules 2A to 2E. Each of the branch pipes of the sludge return pipe 52, the treated water take-out pipe 53, the backflow washing pipe 54, and the chemical supply pipe 55 is provided with an open / close valve (not shown). Further, although not shown, a lift air supply pipe 62 connected to the air lift blower B2 and an air injection pipe 63 connected to the air injection compressor C are also branched so as to correspond to each of the membrane modules 2A to 2E. The branch pipe 63 is provided with an on-off valve.
[0099]
In this embodiment, at the time of backwashing, the backwashing operation is performed only on one selected one of the five membrane modules 2A to 2E. For example, when performing the backwash operation with respect to the first membrane module 2A, the other membrane modules 2B to 2E continue to perform the treated water filtration operation. At this time, among the open / close valves provided in the branch pipes of the respective pipes connected to the first membrane module 2A, the open / close valves provided in the treated water take-out pipe 53 and the branch pipe of the chemical solution supply pipe 55 are closed. Thus, the on-off valve provided on the branch pipe of the backwashing pipe 54 is opened. Further, the on-off valve provided in the air injection pipe 63 is also opened.
[0100]
When the backwashing operation is completed, the on-off valve provided on the branch pipe of the treated water removal pipe 53 is opened, and the on-off valve provided on the branch pipe of the backflow cleaning pipe 54 is closed. The process water filtration operation using 2A to 2E returns.
[0101]
Thereafter, when the backflow cleaning timing of another one of the membrane modules (for example, the second membrane module 2B) is reached, the opening and closing of the on-off valve is switched in the same manner as in the above case, and the backflow cleaning operation for this one membrane module is performed. Be executed. In this way, the filtered water treatment operation is performed in the four or five membrane modules 2A to 2E while the backwash operation is sequentially performed on one membrane module.
[0102]
Similarly, in the chemical cleaning operation, the chemical is supplied to only one of the five membrane modules 2A to 2E and the cleaning is performed. For example, when performing the chemical liquid cleaning operation on the first membrane module 2A, the other membrane modules 2B to 2E continue to perform the treated water filtration operation. At this time, among the on / off valves provided on the branch pipes of the respective pipes connected to the first membrane module 2A, the on / off valves provided on the branch pipe of the chemical solution supply pipe 55 are opened and provided on the other branch pipes. The opened / closed valve is closed. Further, the on-off valve provided in the air injection pipe 63 is also closed.
[0103]
When the chemical cleaning operation is completed, the on-off valve provided on the branch pipe of the chemical supply pipe 55 is closed, and the on-off valves provided on the branch pipes of the sludge discharge pipe 51 and the treated water discharge pipe 53 are opened. The on-off valve provided on the branch pipe of the backwashing pipe 54 is closed, and the operation of filtering the treated water using all the membrane modules 2A to 2E is restored.
[0104]
Thus, in the backwashing operation or the chemical cleaning operation, only one membrane module shifts to the operation, and in the other membrane modules, the treated water filtration operation is continuously performed. For this reason, it is possible to maintain the high performance of the membrane element by the above-mentioned backwashing operation or chemical solution washing operation without greatly reducing the filtration capacity of the entire system.
[0105]
-Other embodiments-
In each of the above-described embodiments and modified examples, the case where the present invention is applied to the water treatment system using the anaerobic-aerobic activated sludge method has been described. The present invention is not limited to this, and can be applied to a water treatment system using another activated sludge method.
[0106]
In each of the above-described embodiments and modifications, the existing sedimentation tank a is removed after the membrane separation unit U is connected to the biological reaction tank 1. The present invention is not limited to this, and the unnecessary precipitation tank a may be newly used as a biological reaction tank. According to this, it is possible to increase the processing capacity of the processing system without changing the existing biological reaction tank 1 to a large one.
[0107]
The installation mode of the membrane separation unit U is not limited to the case where the membrane separation unit U is installed on the ground, but an installation plate is provided so as to cover the upper part of the biological reaction tank 1, and the membrane separation unit U is installed on the installation plate. May be. According to this, the site area for installing the membrane separation unit U is not required separately from the biological reaction tank 1, and the installation area of the whole system can be reduced. Further, as another installation mode of the membrane separation unit U, the membrane separation unit U may be installed inside the unnecessary settling tank a.
[0108]
【The invention's effect】
As described above, the present invention proposes a membrane separation unit newly connected to the biological reaction tank of the existing activated sludge treatment system. In other words, by connecting the membrane separation unit to the biological reaction tank instead of the existing sedimentation tank, the capacity of the system for solid-liquid separation of the treated sludge can be increased without renovating the sedimentation tank. . Therefore, when the processing capacity of the activated sludge treatment system is to be increased, the installation area can be small, and the capacity of the system for solid-liquid separation of the treated sludge can be easily increased without stopping the system. Is possible.
[0109]
Further, the membrane separation unit is provided with a membrane separator for filtering the treated sludge after the biological reaction treatment in the biological reaction tank with a membrane element to obtain treated water, and the treated sludge is introduced into the membrane element at a relatively high speed. While passing through, some of the treated sludge is filtered to extract treated water. In addition, the washing water is periodically passed through the membrane element in a direction opposite to the filtration direction of the treated water, so that solid substances adhering to the membrane element are peeled and removed.
[0110]
For this reason, on the primary side of the membrane element, treated sludge having a flow rate substantially equal to the circulation flow rate in the circulation circuit flows. If the circulation flow rate in this circulation circuit is set relatively high, the primary side of the membrane element Sludge (solid matter) to be attached to the surface is swept away by the circulating flow and returned to the biological reaction tank without adhering to the membrane element. As a result, the amount of sludge (solid matter) attached per unit time on the primary surface of the membrane element is significantly reduced as compared with the case of the conventional immersion type separation membrane unit, and the high filtration capacity is obtained. Can be maintained for a long time.
[0111]
Further, in the present invention, the backwashing operation is performed every predetermined time, whereby the solid matter adhering to the primary side surface of the membrane element is peeled off. For this reason, it is possible to avoid a situation where a large amount of solid matter adheres to the primary side surface of the membrane element, and it is possible to stably perform a filtration operation with a high capacity, and to improve the performance of the activated sludge treatment system. it can. As a result, the amount of treated water obtained per unit time can be significantly increased (increased flux) even with a small membrane area as compared with the conventional one, without increasing the size of the entire system. , High-performance water treatment can be realized. In addition, since the frequency of chemical solution cleaning for the membrane element can be reduced, the operation rate of the water treatment operation (filtration operation) can be improved, and thereby high-performance water treatment can be realized.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a case where a membrane separation unit according to an embodiment is applied in place of an existing sedimentation tank.
FIG. 2 is a diagram illustrating a schematic configuration of a water treatment system according to the first embodiment.
FIG. 3 is a sectional view showing the internal structure of the membrane module.
FIG. 4 is a cross-sectional view showing a state in which a membrane element is housed inside the membrane module.
FIG. 5 is a view for explaining a state inside a membrane element in each step.
FIG. 6 is a timing chart showing the operation of the water treatment system.
FIG. 7 is a diagram illustrating a schematic configuration of a water treatment system according to a first modification.
FIG. 8 is a cross-sectional view illustrating an internal structure of a membrane module according to a second modification.
FIG. 9 is a perspective view of an air diffusion member according to a second modification.
FIG. 10 is a piping diagram of a water treatment system according to a second embodiment.
[Explanation of symbols]
1 Biological reaction tank 2 Membrane module (membrane separator)
11 Denitrification tank (anaerobic tank)
12 Nitrification tank (aerobic tank)
21 Body casing (membrane separator body)
22 Membrane element 52 Sludge return pipes 52a, 53a Branch pipe 53 Treated water outlet pipe (outlet pipe)
55 chemical supply pipe 62d diffuser 64 discharge pipe (discharge means)
65 Storage container V1 Three-way valve (return amount adjusting means)

Claims (7)

It is a membrane separation unit that is newly connected to the biological reaction tank provided in the existing activated sludge treatment system so as to perform solid-liquid separation of the treated sludge that has been subjected to the biological reaction treatment in this biological reaction tank. hand,
The bioreactor includes a membrane separator main body that is installed outside the bioreactor and houses the membrane element, and the membrane separator main body constitutes a circulation circuit that circulates sludge with the bioreactor. A membrane separator configured to obtain treated water by filtering the sludge from the primary side to the secondary side of the membrane element while circulating the sludge in the circulation circuit,
A backwashing means for performing a backwashing operation for allowing the washing water to pass from the secondary side toward the primary side toward the primary side to peel off solid matter attached to the primary side surface of the membrane element; A membrane separation unit for an activated sludge treatment system. The membrane separation unit for an activated sludge treatment system according to claim 1,
Activated sludge treatment characterized by being provided with a bubble supply means for supplying a conveying force to the circulating sludge by supplying air bubbles flowing along the flow direction of the circulating sludge to the primary space of the membrane element through which the circulating sludge flows. Membrane separation unit for system. The membrane separation unit for an activated sludge treatment system according to claim 1 or 2,
A membrane separation unit for an activated sludge treatment system, wherein an air supply means for temporarily passing a relatively large amount of air into a primary space of a membrane element during execution of a backwashing operation is provided. The membrane separation unit for an activated sludge treatment system according to claim 1, 2, or 3,
A chemical solution supply pipe for supplying a chemical solution to the inside of the membrane separator body at the time of cleaning the chemical solution of the membrane separator body is connected to an outlet pipe for leading treated water from the membrane separator body,
A membrane separation unit for an activated sludge treatment system, comprising a chemical cleaning means for performing a chemical cleaning operation for supplying a chemical from the chemical supply pipe through an outlet pipe to the inside of the membrane separator main body. The membrane separation unit for an activated sludge treatment system according to claim 4,
The membrane cleaning unit for an activated sludge treatment system, wherein the chemical cleaning means is configured to execute a chemical cleaning operation at predetermined time intervals. In the membrane separation unit for an activated sludge treatment system according to any one of claims 1 to 5,
The membrane separation unit is connected with an introduction pipe for introducing the treated sludge after the biological reaction treatment in the biological reaction tank into the membrane separation unit,
A membrane separation unit for an activated sludge treatment system, wherein the introduction pipe is provided with a withdrawing means for withdrawing excess sludge in the treated sludge taken out of the biological reaction tank from a circulation circuit. In the membrane separation unit for the activated sludge treatment system according to any one of claims 1 to 6,
A plurality of membrane separators are connected in parallel to the biological reaction tank, and the backwashing means performs the backwashing operation on only one selected from the plurality of membrane separators at the time of backwashing. A membrane separation unit for an activated sludge treatment system, which is configured as described above.

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