JP5048637B2 - Membrane separator - Google Patents

Description

  The present invention relates to a membrane separation apparatus that performs solid-liquid separation using a membrane module using a filtration membrane in a water treatment apparatus that treats sewage, industrial wastewater, and the like by an activated sludge treatment method.

  In recent years, in water treatment equipment, when sludge liquid after biological reaction treatment in a biological reaction tank containing activated sludge liquid is solid-liquid separated, it is not affected by the sedimentation property of activated sludge liquid, and it is a clear and advanced treatment of water quality. Membrane separation methods using membrane separation technology are attracting attention as water treatment methods that can obtain water and make the treatment facility compact. In this method, solid-liquid separation of activated sludge and treated water has been mainly studied and put into practical use by immersing a filtration membrane having a fine pore size in a biological reaction tank.

  The membrane module (membrane separation unit) immersed in the biological reaction tank as described above is an air diffuser that supplies air for cleaning the membrane surface from the bottom, for backwashing the membrane surface with treated water or clear water In general, it has a mechanism and a mechanism for injecting a cleaning agent such as hypochlorous acid, and these prevent the clogging of the film surface and continue processing. And since the membrane surface will be clogged due to the adhesion of organic substances etc. when used for a long time, the membrane module is periodically taken out from the biological reaction tank and filled with cleaning chemicals such as hypochlorous acid adjusted to a predetermined concentration. It was necessary to perform immersion cleaning in the immersion cleaning tank.

  In a facility that treats a large amount of water, such as a sewage treatment facility, a membrane module to be used is large, and a crane or the like must be used to take it out of a biological reaction tank, which is not easy. Therefore, in order to simplify the labor of immersion cleaning, a water treatment apparatus has been devised in which a biological reaction tank for biological treatment of sewage and a membrane separation tank for solid-liquid separation are separately installed (non-patent document). 1).

  Non-Patent Document 1 discloses that, as a membrane separation activated sludge method (MBR), a separation operation between activated sludge and treated water, which is performed by gravity sedimentation in a final sedimentation basin or the like in the conventional activated sludge method, is performed using a membrane, and It is described that a membrane separation tank is preferably provided separately from the biological reaction tank. In other words, the provision of a membrane separation tank necessitates the provision of a sludge liquid circulation line or pump between the membrane separation tank and the biological reaction tank. It has excellent flexibility in operation such as changing the number of operating series according to the amount of water, and has the advantage that it is not necessary to move the membrane module during immersion cleaning.

  And when installing a membrane separation tank separately, in order to maintain the sludge liquid flow rate in the biological reaction tank and prevent the sludge concentration from becoming too high in the membrane separation tank, the sludge between the biological reaction tank and the membrane separation tank It is necessary to circulate the liquid.

In order to prevent sludge from adhering to the membrane, a method of supplying air for cleaning the membrane surface from the lower part of the membrane module in the membrane separation tank and preventing sludge from adhering to the membrane has been implemented. The air supply to the membrane module also has a function of causing a swirl flow in the sludge liquid in the membrane separation tank and making the sludge concentration in the membrane separation tank uniform.
Journal of Sewerage Association Vol.43, No.528, p87-98, Survey on membrane separation activated sludge process in European sewage treatment facilities, 2006

  By the way, when the biological reaction tank for biological treatment of raw water and the membrane separation tank for solid-liquid separation are separated, the sludge liquid is circulated between the biological reaction tank and the membrane separation tank as described above. In general, it is necessary to circulate the sludge liquid by installing a pump. In this case, the labor required to carry out the immersion cleaning of the membrane module is compared to the method of performing membrane separation in a biological reaction tank. Although it is simple, extra power such as a pump for circulating the sludge liquid is required, which increases the processing cost.

  The present invention has been made in view of the above points, and by devising a connection method between the biological reaction tank and the membrane separation tank, the power required for the sludge liquid circulation between the biological reaction tank and the membrane separation tank can be reduced and more efficiently. An object of the present invention is to provide a membrane separation apparatus capable of performing a membrane separation treatment.

The membrane separation apparatus of the present invention is a membrane separation apparatus for solid-liquid separation of sludge liquid after biological reaction treatment in a biological reaction tank containing activated sludge liquid,
A membrane separation tank installed separately from the biological reaction tank;
A plurality of membrane modules arranged vertically in the membrane separation tank;
In order to circulate sludge liquid in the biological reaction tank and the membrane separation tank, a sludge liquid supply pipe connecting the membrane separation tank and the biological reaction tank at the lower part,
In order to circulate sludge liquid in the biological reaction tank and the membrane separation tank, a sludge liquid return pipe connecting the membrane separation tank and the biological reaction tank at the upper part,
Air supply means for ejecting air into the membrane separation tank,
The sludge liquid supply pipe has a downstream end portion that penetrates to the inside of the membrane separation tank, extends to the lower part of each of the membrane modules, and opens upward corresponding to the bottom position of each membrane module. And
An air supply port of the air supply means which is installed in the separation tank side opening and jets air toward the membrane module;
The sludge liquid is fed into the membrane separation tank from the separation tank side opening of the sludge liquid supply pipe by the air ejected from the air supply port, and the membrane cleaning of the membrane module is performed. Is.

  At that time, it is preferable that the lower part of the membrane module is fixed in the separation tank side opening of the sludge liquid supply pipe, and the extension cylinder part of the separation tank side opening is formed surrounding the lower outer periphery of the membrane module. It is.

  Further, the upstream end portion of the sludge liquid supply pipe installed in the biological reaction tank is configured to be opened downward and installed in a downward flow portion in the circulating flow of sludge liquid in the biological reaction tank. Also good.

Further, the air flow rate supplied from the air supply port to the membrane separation tank by the air supply means is Qa [Nm ³ / h], the air flow rate is Qw [m ^3]. / h], it is preferable that the pumping coefficient k = 1− [1 ÷ (Qa ÷ Qw + 1)] is defined in a range of 0.2 to 0.8.

  According to the membrane separation apparatus of the present invention, a plurality of membrane modules are arranged vertically in a membrane separation tank installed separately from a biological reaction tank containing activated sludge, and the biological reaction tank and the membrane separation tank are arranged. In order to circulate the sludge liquid, the membrane separation tank and the biological reaction tank are connected by the lower sludge liquid supply pipe and the upper sludge liquid return pipe, respectively, and the downstream end portion of the sludge liquid supply pipe is membrane-separated. Air that penetrates to the inside of the tank, extends to the bottom of each of the membrane modules, and has a separation tank side opening that opens upward corresponding to the position of the bottom of each membrane module, while jetting air into the membrane separation tank Since the supply means has an air supply port for ejecting air toward the membrane module in the separation tank side opening, the air ejected from the air supply port causes the separation tank side opening of the sludge liquid supply pipe Sludge liquid from biological reaction tank through Since it can be fed into the membrane separation tank and the membrane module can be washed, the power required for sludge liquid circulation between the membrane separation tank and the biological reaction tank can be reduced, and the sludge in the membrane separation tank can be reduced. The liquid concentration can be kept constant, and the solid-liquid separation of the sludge liquid after the biological reaction treatment by the membrane module can be stably continued.

  In particular, the lower sludge liquid supply pipe from the biological reaction tank to the membrane separation tank penetrates into the membrane separation tank, and this sludge liquid supply pipe has an opening on the separation tank side only, and the separation tank side Each membrane module is installed at the upper part of the opening, and the specific gravity of the sludge liquid in the sludge liquid supply pipe in the membrane separation tank due to the mixing of the blown air is caused by the ejection of air for membrane cleaning. At the same time as the specific gravity of the connecting part between the reaction tank and the sludge liquid supply pipe becomes lighter, the sludge liquid is sequentially pushed out from the opening on the separation tank side of the sludge liquid supply pipe to the membrane separation tank. And is sent to move up. Therefore, the sludge liquid in the biological reaction tank is sucked into the sludge liquid supply pipe, flows into the membrane separation tank, and the increased amount of sludge liquid in the membrane separation tank is transferred to the biological reaction tank by the upper sludge liquid return pipe. As returned, the sludge is circulated between the biological reaction tank and the membrane separation tank.

  In addition, if the separation tank side opening is open to the sludge liquid supply pipe in the membrane separation tank other than the upward direction, the sludge liquid in the membrane separation tank is sucked into the sludge liquid supply pipe from this separation tank side opening. Thus, the sludge liquid is not sucked into the sludge liquid supply pipe from the biological reaction tank, and the above-described sludge liquid circulation action due to the air ejection cannot be obtained.

  At that time, when the lower part of the membrane module is fixed in the separation tank side opening of the sludge liquid supply pipe and the extension cylinder part of the separation tank side opening is formed surrounding the lower outer periphery of the membrane module, The feeding characteristic of the sludge liquid in the supply pipe and the blocking characteristic of the membrane clogging with the supply air can be secured efficiently and satisfactorily.

  Further, when the upstream end portion of the sludge liquid supply pipe installed in the biological reaction tank is configured to be opened downward and installed in the downward flow portion in the circulating flow of sludge liquid in the biological reaction tank, the biological reaction While ensuring good biological treatment characteristics in the tank, it is possible to suppress the inflow of air into the sludge liquid supply pipe and maintain a desired amount of sludge liquid circulation.

  In the biological reaction tank, there are various biological treatment methods for sewage, but the sludge liquid supplied to the membrane separation tank is often a biological reaction tank that performs aerobic biological treatment. And when a biological reaction tank is an aerobic tank, air is supplied to this biological reaction tank. In the present invention, air is supplied to the separation tank side opening of the sludge liquid supply pipe, the sludge liquid in the vicinity of the separation tank side opening is pushed out by the lifting force by the air, the specific gravity difference in the sludge liquid supply pipe and the separation tank The sludge liquid is sucked from the biological reaction tank due to the negative pressure accompanying the outflow of the sludge liquid from the side opening, and excess sludge liquid is transferred from the membrane separation tank to the biological reaction tank by the sludge liquid return pipe due to the pressure difference such as the liquid level difference. Since it is a device that circulates sludge liquid so as to return, if bubbles are mixed into the sludge liquid supply pipe from the biological reaction tank, the specific gravity difference is reduced and the suction force is reduced, and the amount of sludge liquid circulated is reduced. End up.

  For this purpose, the reaction tank side opening at the upstream end portion of the sludge liquid supply pipe in the biological reaction tank is directed downward to the downward flow section in the circulation flow of the sludge liquid in the biological reaction tank accompanying the air supply for aerobic treatment. When installed open, it is possible to reduce the inhalation of bubbles and suppress the decrease in the amount of sludge liquid circulation. In particular, when the air (oxygen) supply means in the aerobic tank as the biological reaction tank is an air diffuser using fine bubbles, the oxygen dissolution efficiency is high, so the flow rate of air to be blown is small and the bubbles themselves are small. In addition, the amount of air bubbles flowing into the sludge liquid supply pipe from the biological reaction tank side can be reduced.

The air flow rate supplied from the air supply port to the membrane separation tank by the air supply means is Qa [Nm ³ / h], and the sludge flow rate supplied to the membrane separation tank is Qw [m ³ / h. ], If the pumping coefficient k = 1− [1 ÷ (Qa ÷ Qw + 1)] is specified in the range of 0.2 to 0.8, membrane separation of the membrane module is prevented and good separation processing is continued. Can do.

  In other words, the air flow rate for blocking the membrane module is secured, and the flow rate of the sludge liquid associated therewith, that is, the circulation supply of the sludge liquid from the biological reaction tank, is secured so that the MLSS concentration in the membrane separation tank does not become excessive. Thus, the membrane separation performance can be maintained. When the sludge liquid flow rate increases beyond the processing capacity of the membrane module, the air flow rate for obtaining the sludge liquid flow rate becomes enormous and inappropriate.

  Hereinafter, membrane separation apparatuses according to first to fourth embodiments of the present invention will be described in detail with reference to the drawings. 1 to 3 are elevation views showing schematic configurations of membrane separation apparatuses according to first to third embodiments of the present invention, respectively, and FIG. 4 is a diagram of a membrane separation apparatus according to the fourth embodiment of the present invention. It is a top view which shows schematic structure.

<First Embodiment>
As shown in FIG. 1, a membrane separation apparatus 10 of this embodiment includes a membrane separation tank 30 installed separately from a biological reaction tank 20 that contains a sludge liquid obtained by mixing activated sludge and raw water. The membrane separation apparatus 10 is for solid-liquid separation of the sludge liquid after biological reaction treatment in the biological reaction tank 20 into activated sludge and treated water. A plurality of membrane modules 40 are arranged, and each membrane module 40 is connected to a drain pipe 50 having a suction pump (not shown), and the treated water that has permeated through the filtration membrane 41 is discharged to perform membrane separation.

  The membrane module 40 includes a filtration membrane 41 formed of a microporous membrane such as a hollow fiber membrane formed in a tube shape or a membrane shape, and a lower support 42 holding a lower end by arranging a plurality of the filtration membranes 41 The upper support 43 holds the upper end. The upper support 43 incorporates a water collection part (not shown) in which treated water that has passed through the filtration membrane 41 is collected, and includes a drain port 43a to which the drain pipe 50 is connected. The drain pipe 50 is led out of the membrane separation tank 30 and connected to a suction pump (not shown).

  A plurality of membrane modules 40 corresponding to the treatment flow rate are installed in one membrane separation tank 30 and predetermined so that sludge liquid can flow in the tank of the membrane separation tank 30 from below to above. Are arranged in rows (see FIG. 4), arcs, etc.

  In order to circulate the sludge liquid in the biological reaction tank 20 and the membrane separation tank 30, the biological reaction tank 20 and the membrane separation tank 30 are connected by a lower sludge liquid supply pipe 60 and an upper sludge. The liquid return pipe 70 is connected. The sludge liquid supply pipe 60 is connected to air supply means 80 for blowing air into the tank of the membrane separation tank 30 and supplied with pressurized air.

  The upstream end portion of the sludge liquid supply pipe 60 is connected to the lower wall surface of the biological reaction tank 20, opens to the wall surface below the liquid surface, and in the vicinity of the intermediate portion accommodated in the biological reaction tank 20 The reaction tank side opening 61 into which the sludge liquid flows.

  Further, the downstream end portion of the sludge liquid supply pipe 60 is connected to the wall surface near the bottom of the membrane separation tank 30 and penetrates through the wall surface to penetrate the inside of the membrane separation tank 30. The separation tank side opening 62 is opened upward corresponding to the position of the bottom of each membrane module 40.

  The lower support 42 at the lower part of the membrane module 40 is fixedly held in the separation tank side opening 62 of the sludge liquid supply pipe 60, and an extension cylinder is provided around the separation tank side opening 62. 63 extends upward so as to surround the outer periphery of the lower part of the membrane module 40. It is preferable that the extension cylinder portion 63 is formed so as to surround from the lower part of the membrane module 40 to at least three times the pipe diameter of the sludge liquid supply pipe 60.

  In addition, the air supply port 81 of the air supply means 80 is installed in the separation tank side opening 62 of the sludge liquid supply pipe 60 so as to eject air toward the membrane modules 40. This air supply means 80 includes an air pipe 82 connected to an air supply port 81 corresponding to each membrane module 40, and is connected to an air pump 83 to supply pressurized air. The air supply port 81 pushes up the sludge liquid existing in the vicinity of the separation tank side opening 62 of the sludge liquid supply pipe 60 from the separation tank side opening 62 to the extension cylinder part 63, and the inside of the membrane separation tank 30 It acts to discharge. For this purpose, the air supply port 81 is disposed below the separation tank side opening 62 so that the jetted air is mixed with the sludge liquid inside the sludge liquid supply pipe 60 and moves in the direction of the separation tank side opening 62. Consists of one or more air outlets installed at a position. In the case where the extension cylinder part 63 is installed, the opening position of the air supply port 81 may be arranged in the extension cylinder part 63.

  On the other hand, the upstream end of the sludge liquid return pipe 70 is connected to the upper wall surface of the membrane separation tank 30 and opens to the wall surface in the vicinity of the liquid level, so that the excess return stored in the membrane separation tank 30 is obtained. It becomes the upstream opening 71 into which the sludge liquid flows. Further, the downstream end of the sludge liquid return pipe 70 is connected to the upper wall surface of the biological reaction tank 20, and opens to the wall surface above the liquid level at the normal water level to return the sludge to the biological reaction tank 20. It becomes the downstream opening 72 through which the liquid flows out.

  The sludge liquid return pipe 70 is desirably installed so as to have a gentle downward slope from the membrane separation tank 30 to the biological reaction tank 20 in order to prevent the backflow of sludge.

  In addition, the excess sludge generated according to the treatment in the biological reaction tank 20 is drawn out separately and discharged to the outside.

  Explaining the operation of the first embodiment as described above, when air is ejected from the air supply port 81 of the air supply means 80, the bubbles are mixed into the sludge liquid existing inside the sludge liquid supply pipe 60. As a result, the lifting force due to the buoyancy of the bubbles acts, and the specific gravity of the sludge liquid in the separation tank side opening 62 of the sludge liquid supply pipe 60 is reduced by mixing air, so that the sludge liquid supply pipe 60 has a separation tank side. The sludge liquid is pushed upward from the opening 62. As the sludge liquid rises and is discharged sequentially from the separation tank side opening 62, the sludge liquid is sucked and moved from the inside of the sludge liquid supply pipe 60 toward the separation tank side opening 62, and the biological reaction tank. A flow in which the sludge liquid in 20 flows into the sludge liquid supply pipe 60 from the reaction tank side opening 61 occurs.

  The sludge liquid that has moved upward along the outer periphery of the extension cylinder 63 and the lower part of the membrane module 40 from the separation tank side opening 62, the moisture permeates the filtration membrane 41 by contacting with the filtration membrane 41 of the membrane module 40, The permeated treated water is discharged from the drain port 43a of the upper support 43 through the drain pipe 50. At the same time, it is possible to maintain stable filtration characteristics by preventing sludge adhering to the surface of the filtration membrane 41 of the membrane module 40 from coming into contact with the surface by washing and removing the sludge. .

  The sludge liquid in the membrane separation tank 30 is increased by the sludge liquid that is sequentially pushed out from the upper end of the extension cylinder portion 63 to the membrane separation tank 30 and moves upward, and the liquid level rises to increase the sludge liquid return pipe 70. When the height of the upstream opening 71 is reached, the upper sludge liquid in the membrane separation tank 30 is fed to the biological reaction tank 20 through the sludge liquid return pipe 70.

  In addition, when the biological reaction tank 20 to which the sludge liquid supply pipe 60 is connected is an aerobic tank 20C and there is a swirl flow R of sludge liquid accompanying air supply for aerobic treatment as in a third embodiment described later. In the upstream portion of the sludge liquid supply pipe 60, the tip end portion 60a penetrates into the biological reaction tank 20, the upstream end portion is bent downward, and the reaction tank side opening 61 has the swirl flow R. It is installed so as to open downward in the downward flow part. By preventing the swirling sludge liquid from directly flowing into the opening of the sludge liquid supply pipe 60, the sludge liquid is provided so as to suppress a decrease in the amount of sludge circulation due to the suction of bubbles. The same applies to a second embodiment described later.

  As described above, in the present embodiment, the sludge liquid treated in the biological reaction tank 20 is circulated to the membrane separation tank 30 only by the ejection of air from the separation tank side opening 62 that opens upward in the membrane separation tank 30. To be sent. The circulation flow rate of the sludge liquid increases in accordance with the flow rate of air blown by the air supply means 80.

Then, the air flow rate supplied to the membrane separation tank 30 from the air supply port 81 provided in the separation tank side opening 62 of the sludge liquid supply pipe 60 is defined as Qa [Nm ³ / h]. When the sludge flow rate supplied to is Qw [m ³ / h], the pumping coefficient k = 1− [1 ÷ (Qa ÷ Qw + 1)] is defined in a range of 0.2 to 0.8.

  In particular, as in this embodiment, the air flow rate Qa for supplying the entire amount of the circulating sludge liquid by the jet air becomes a relatively large amount, and the pumping coefficient k tends to be a large value. Appropriate relationship between the air flow rate Qa and the sludge liquid flow rate Qw will be described in the examples described later.

  Then, by supplying the air flow rate Qa, it is possible to prevent the membrane module 40 from being blocked and to maintain good separation performance. In other words, the air flow for blocking the membrane module 40 is secured, and the flow rate of the sludge liquid, that is, the supply of the sludge liquid from the biological reaction tank 20 is secured, so that the MLSS concentration in the membrane separation tank (in 1 liter) Membrane separation performance can be maintained by preventing activated sludge suspended solids mg) from becoming excessive. If the sludge liquid flow rate exceeds the processing capacity of the membrane module 40, the air flow rate for obtaining the sludge liquid flow rate becomes enormous and inappropriate.

<Second Embodiment>
As shown in FIG. 2, the membrane separation apparatus 11 of this embodiment includes a membrane separation tank 30 installed separately from the biological reaction tank 20 containing sludge liquid, as in the first embodiment. A plurality of membrane modules 40 are arranged in the separation tank 30, and a drain pipe 50 is connected to each membrane module 40. Further, the biological reaction tank 20 and the membrane separation tank 30 are provided at the bottom for circulation of sludge liquid. The sludge liquid supply pipe 60 and the upper sludge liquid return pipe 70 are connected. The sludge liquid supply pipe 60 in which the reaction tank side opening 61 is connected to the biological reaction tank 20 is connected to the separation tank side opening 62 corresponding to the bottom position of each membrane module 40. The air supply means 80 for jetting air is connected to the tank, and pressurized air is jetted from the air supply port 81.

  The downstream end portion of the sludge liquid supply pipe 60 penetrates the wall surface of the membrane separation tank 30 and the tip portion penetrates to the inside of the membrane separation tank 30 and branches as necessary. The separation tank side openings 62 are opened upward corresponding to the bottom positions of the membrane modules 40, respectively. Further, the lower support 42 in the lower part of the membrane module 40 is fixedly held in the separation tank side opening 62 of the sludge liquid supply pipe 60, and an extension cylinder 63 is formed around the separation tank side opening 62. The lower part of 40 is surrounded and extended upward. An air supply port 81 of the air supply means 80 is installed in the separation tank side opening 62 of the sludge liquid supply pipe 60 so as to eject air toward the membrane modules 40. On the other hand, in the sludge liquid return pipe 70, the upstream opening 71 opens on the wall surface near the liquid surface of the membrane separation tank 30, and the downstream opening 72 opens on the wall surface above the liquid surface of the biological reaction tank 20. Then, the excess sludge liquid in the membrane separation tank 30 is returned to the biological reaction tank 20. In addition, the same code | symbol is attached | subjected to the component similar to 1st Embodiment, and the description is abbreviate | omitted.

  In the present embodiment, a configuration different from that of the first embodiment described above is that a sludge liquid feeding means 90 that feeds sludge liquid by power from the bottom of the biological reaction tank 20 to the bottom of the membrane separation tank 30 is installed separately. It is a point that has been. This sludge liquid feeding means 90 has one end connected to the biological reaction tank 20 and the other end branched and connected to a plurality of positions of the membrane separation tank 30 and opened in the middle of the sludge liquid feeding pipe 91. A feed pump 92 that has been provided.

  That is, the circulating supply of sludge liquid accompanying the air ejection from the air supply port 81 to the membrane separation tank 30 by the air supply means 80 of the present embodiment is used as an auxiliary, and is necessary for the membrane cleaning of the membrane module 40. Priority is given to the supply of the air flow rate, and the ejection flow rate is set lower than the air flow rate required for the sludge liquid circulation.

  The operation of the second embodiment as described above will be described. Also in the present embodiment, by ejecting air from the air supply port 81 of the air supply means 80, the sludge liquid supply action and the membrane cleaning action of the membrane module 40 are substantially the same as in the first embodiment. However, the sludge liquid supply capacity, that is, the sludge liquid flow rate sent from the biological reaction tank 20 to the membrane separation tank 30 is not the total amount of the required amount, but the total amount with the supply amount by the sludge liquid feeding means 90 using power. Is set to be the required amount. Then, the sludge liquid feed means 90 can reduce the power required for driving the feed pump 92 compared with the case where the entire amount is supplied, and the action of membrane cleaning and concentration equalization accompanying the air ejection can be obtained.

As described above, in the present embodiment, the supply of sludge liquid from the biological reaction tank 20 to the membrane separation tank 30 is supplementarily utilized by air ejection. Even in this case, when the air flow rate supplied to the membrane separation tank 30 is Qa [Nm ³ / h] and the sludge liquid flow rate supplied to the membrane separation tank 30 is Qw [m ³ / h] The pumping coefficient k = 1- [1 ÷ (Qa ÷ Qw + 1)] is defined in a range of 0.2 to 0.8, but the pumping coefficient k tends to be a small value (Examples described later) reference).

<Third Embodiment>
As shown in FIG. 3, the membrane separation apparatus 12 of the present embodiment includes a biological reaction tank 20 constituted by three tanks, and a membrane separation tank 30 installed separately from the biological reaction tank 20. . The biological reaction tank 20 includes an anaerobic tank 20A, an anaerobic tank 20B, and an aerobic tank 20C. A raw water pipe 25 is connected to the first anaerobic tank 20A, and raw water is supplied by a pump 26. The second tank is fed from the anaerobic tank 20B to the third aerobic tank 20C, and the upstream end of the sludge liquid supply pipe 60 is inserted into the aerobic tank 20C so as to suck the sludge liquid. Yes.

  In the tank of the membrane separation tank 30, as in the first and second embodiments described above, a plurality of membrane modules 40 are arranged vertically, and a drain pipe 50 is connected to each membrane module 40. The treated water that has passed through the filtration membrane 41 is discharged to perform membrane separation. The structure of the membrane module 40 is the same, and includes a filtration membrane 41, a lower support 42, and an upper support 43, and a drain pipe 50 is connected to the upper support 43.

  In order to circulate the sludge liquid between the aerobic tank 20C of the third tank of the biological reaction tank 20 and the membrane separation tank 30, the aerobic tank 20C and the membrane separation tank 30 are provided with a sludge liquid supply pipe 60 at the bottom. And at the upper sludge liquid return pipe 70.

  As in the first and second embodiments described above, the sludge liquid supply pipe 60 in the membrane separation tank 30 is connected to an air supply means 80 for jetting air into the tank of the membrane separation tank 30; Pressurized air is supplied. That is, the downstream end of the sludge supply pipe 60 is connected to the wall surface in the vicinity of the bottom of the membrane separation tank 30 and penetrates the wall surface to penetrate the tip part to the inside of the membrane separation tank 30. Branching, extending to the lower part of each of the membrane modules 40, the separation tank side openings 62 are opened upward corresponding to the bottom positions of the membrane modules 40, respectively. The lower support 42 at the bottom of the membrane module 40 is fixedly held in the separation tank side opening 62, and the extension cylinder 63 surrounds the lower outer periphery of the membrane module 40 around the opening. It is formed to extend. Further, an air supply port 81 is installed in the separation tank side opening 62 so as to eject air toward each membrane module 40, and pressurized air is supplied through the air pipe 82.

  The upstream portion of the sludge liquid supply pipe 60 is connected to a wall surface below the liquid level of the aerobic tank 20C of the third tank of the biological reaction tank 20, and the tip 60a passes through this wall surface. After penetrating the inside of the aerobic tank 20C, it is bent downward, and the reaction tank side opening 61 at the tip opens downward. In the portion of the aerobic tank 20C where the reaction tank side opening 61 at the front end is opened, there is a swirl flow R of sludge accompanying the ejection of air for aerobic treatment, as will be described later. It is installed so that it may open downward in the downward flow part. From the reaction tank side opening 61 that opens downward, the sludge liquid in the upward flow part with a large amount of mixed air in the swirling sludge liquid flow does not flow directly, and while suppressing the inflow of air, the aerobic tank 20C It is provided to suck the sludge liquid.

  On the other hand, the sludge liquid return pipe 70 has an upstream opening 71 connected to the upper wall surface of the membrane separation tank 30, opened to a wall surface near the liquid surface, and a downstream part being anaerobic of the biological reaction tank 20. Connected to the return branch pipes 73A, 73B, 73C installed in the upper part of the tank 20A, the oxygen-free tank 20B, and the aerobic tank 20C, respectively, the excess sludge liquid in the membrane separation tank 30 is returned respectively. It is drawn out and discharged through the discharge valve 74.

  In the biological reaction tank 20, there are various raw water purification treatment capacities depending on the activated sludge that is input, and many kinds of microorganisms such as bacteria and protozoa live in this activated sludge. The reaction conditions are changed according to the components contained therein. The first anaerobic tank 20A is for anaerobic treatment in which anaerobic microorganisms that are difficult to survive in the presence of oxygen are activated to decompose pollutants in the raw water. is there. The second oxygen-free tank 20B is an oxygen-free tank where denitrifying bacteria use organic matter as an energy source to reduce nitrite nitrogen and nitrate nitrogen to nitrogen gas, etc. Nitrogen in raw water can be removed.

  The third tank, the aerobic tank 20C, stabilizes raw water by decomposing organic matter with aerobic bacteria, molds, protozoa, algae, plankton and other aerobic microorganisms that grow and proliferate in the presence of air. In this aerobic tank 20C, an aeration device 85 is installed to supply air (oxygen), and stirring is performed by the swirl flow R accompanying the supply of air. The air diffuser 85 includes an air diffuser port 86 disposed in the center of the bottom of the aerobic tank 20C. The air diffuser 87 from the air pump 88 is connected to the air diffuser 85 so as to eject air bubbles. Along with the supply of air, an upward flow is generated in the aerobic tank 20C in the air ejection portion above the air diffusion port 86 near the center, and a downward flow is generated in the peripheral portion. A sludge circulation flow (swirl flow) is generated, and with respect to this swirl flow R, the reaction tank side opening 61 at the tip of the sludge liquid supply pipe 60 as described above is a part of the downward flow with less air mixing. The air is opened downward to minimize air suction.

  As described above, when the supply of air in the aerobic tank 20C is such that fine bubbles are mixed into the sludge liquid by the air diffuser 85, the oxygen dissolution efficiency is high, so that the aerobic tank 20C The flow rate of air to be blown is small, and the bubbles themselves are small, so that the amount of bubbles flowing into the sludge liquid supply pipe 60 from the aerobic tank 20C side can be reduced.

  Explaining the operation of the third embodiment as described above, the operation accompanying the ejection of air from the air supply port 81 of the air supply means 80 in the membrane separation tank 30 is substantially the same as that of the first embodiment. It has a sludge liquid circulation action and a membrane cleaning action. That is, air is supplied to the separation tank side opening 62 of the sludge liquid supply pipe 60 inside the membrane separation tank 30, and the sludge liquid in the vicinity of the opening is pushed out by the lifting force by the air, and the sludge liquid supply pipe 60 The sludge liquid is sucked in from the aerobic tank 20C by the specific gravity difference and negative pressure, and the sludge liquid is circulated so that the sludge liquid return pipe 70 returns from the membrane separation tank 30 to the aerobic tank 20C by the pressure difference such as the liquid level difference. . In this case, for example, in the aerobic tank 20C, the swirl flow R is generated in the sludge liquid due to air mixing due to the aerobic reaction. Therefore, when the sludge liquid in this portion is sucked, bubbles are sucked into the sludge liquid supply pipe 60 together with the sludge liquid. In this case, the difference in specific gravity is reduced, the sludge liquid suction force is reduced, the amount of sludge liquid sucked from the aerobic tank 20C is reduced, and the treatment in the membrane separation tank 30 is accompanied by the reduction of the circulating liquid flow rate. The amount will decrease.

  On the other hand, in the present embodiment, by opening the reaction tank side opening 61 at the upstream end portion of the sludge liquid supply pipe 60 in the aerobic tank 20C downward to the downward flow part of the swirl flow R of the sludge liquid, Since the sludge liquid in the part where air contamination is reduced is sucked in, the specific gravity difference is large and the suction negative pressure can be maintained, and the decrease in the sludge flow rate from the aerobic tank 20C can be suppressed. The processing efficiency can be maintained.

<Fourth Embodiment>
As shown in FIG. 4, the membrane separation apparatus 13 of the present embodiment includes a plurality of membrane separation tanks 30 in which sludge liquid is circulated from the biological reaction tank 20, in the illustrated case, the first membrane separation tank 30 </ b> A and the second membrane separation. This is an example provided with three membrane separation tanks, tank 30B and third membrane separation tank 30C.

  Each of the membrane separation tanks 30A to 30C is provided with six membrane modules 40, and the sludge supply pipe 60 in which the reaction tank side opening 61 at one end is connected to the lower part of the biological reaction tank 20 Branches to three sludge liquid supply pipes 60A, 60B, 60C (may be connected independently without branching), and open / close valves 65A, 65B, 65C are installed and connected to the lower part of each membrane separation tank 30A-30C Is done. Each sludge liquid supply pipe 60A-60C penetrates into the inside of each membrane separation tank 30A-30C and further branches into a branch pipe, and each tip extends to a position below the respective membrane module 40, and the first As in the embodiment, the separation tank side opening 62 (not shown) opens upward, the air supply port 81 of the air supply means 80 (not shown) opens, and air is ejected to each membrane module 40. It is configured.

  Although the detailed structure is not shown, the sludge liquid return pipe 70 that connects each of the membrane separation tanks 30A to 30C and the biological reaction tank 20 at the top, and the treated water that has passed through the filtration membrane 41 of each membrane module 40 is discharged. A drainage pipe 50 or the like is installed in the same manner as in the first embodiment.

  In the state shown in FIG. 4, in the first membrane separation tank 30A and the second membrane separation tank 30B, the open / close valves 65A and 65B of the sludge liquid supply pipes 60A and 60B are opened, and the air supply means 80 Air is ejected from below into the membrane modules 40 in the membrane separation tanks 30A and 30B, and sludge is circulated between the biological reaction tanks 20 as described in the first embodiment, and each membrane module is circulated. The treated water that has passed through the filtration membrane 41 is sucked at 40, and the water treatment discharged through the drain pipe 50 is continued.

  On the other hand, in the third membrane separation tank 30C, the membrane separation process is stopped and the immersion cleaning process is performed. The open / close valve 65C of the sludge supply pipe 60C for the third membrane separation tank 30C is closed to stop the circulation of the sludge, and the internal sludge is discharged to clean the tank with hypochlorous acid and the like. The chemical solution is charged and the membrane module 40 and the like are cleaned in the tank.

  The cleaning treatment as described above is sequentially performed at predetermined intervals for the other first membrane separation tank 30A and the second membrane separation tank 30B, and a plurality of membrane separation tanks are installed. Thus, the entire membrane separation device 13 is configured such that maintenance can be performed while continuing the processing while partially reducing the processing capacity without stopping the water treatment.

  The first to fourth embodiments described above include the following modifications. The lower part of the membrane module 40 installed in the membrane separation tank 30 is surrounded and covered by the extension cylinder part 63 of the sludge liquid supply pipe 60. You may form the extension cylinder part so long that it covers. The extension cylinder part 63 of the sludge liquid supply pipe 60 may be further extended and the tip of the extension cylinder part 63 and the tip of the sludge liquid return pipe 70 may be connected. The membrane separation tank is configured in the extension cylinder portion 63 containing the module 40, that is, in the sludge liquid supply pipe 60 and / or the sludge liquid return pipe 70.

  Further, in the membrane separation tank 30, an agitator or an agitation / mixing means by feeding a liquid mixture may be used as an auxiliary mixing method.

As an example of the present invention, a test apparatus including a cylindrical membrane module having a diameter of 16 cm, a sludge liquid supply pipe having a diameter of 20 cm, and a membrane separation tank having an effective capacity of 0.75 m ³ was operated.

In order to confirm whether necessary and sufficient circulating water volume (sludge liquid flow rate) can be secured by supplying membrane cleaning air, tap water is stored in a 4m deep water tank as a simulated biological reaction tank, and 50cm above the bottom of the tap water storage tank. In addition, a sludge liquid supply pipe connected to the membrane separation tank was installed. The sludge supply pipe rises upward in the membrane separation tank, and is provided with an extension cylinder that rises to cover the lower 100 cm of the membrane module. Air is supplied from the cleaning air supply means 20 cm above the bottom of the startup pipe. Was supplied at 8 Nm ³ / h, and the flow rate of the circulating liquid flowing into the membrane separation tank through the sludge liquid supply pipe was about 3 m ³ / h. When continuous operation was performed with a filtration water volume of 0.5 m ³ / h for one membrane module, the sludge liquid return from the membrane separation tank was 2.5 m ³ / h.

  When sludge liquid is actually passed through, the MLSS concentration in the membrane separation tank is higher than that in the biological reaction tank due to filtration, but this circulation rate can be suppressed to about 120% of the MLSS concentration in the biological reaction tank. It was confirmed that stable filtration operation was possible.

  Next, the data which prescribes | regulates the above-mentioned pumping coefficient k in the range of 0.2-0.8 is demonstrated.

As described above, the pumping coefficient k is obtained by k = 1− [1 ÷ (Qa ÷ Qw + 1)] where Qa [Nm ³ / h] is an air flow rate and Qw [m ³ / h] is a sludge liquid flow rate. When the pumping coefficient k is higher than the upper limit boundary value, the sludge liquid flow rate Qw to the membrane separation tank decreases, and the membrane separation tank MLSS concentration increases with the amount of processing liquid discharged as filtration continues by the membrane module. There is a problem that it becomes higher and hinders filtration by the membrane module. On the other hand, when the pumping coefficient k is lower than the lower limit boundary value, the sludge liquid flow rate Qw becomes excessive and there is a problem of excessive input of power, or when the air flow rate Qa is excessively low, the membrane module is insufficiently washed, which is also filtered. We have found a suitable range to solve these problems.

In the above-described embodiment, the air flow rate Qa is changed to 3 [Nm ³ / h], 5 [Nm ³ / h], and 10 [Nm ³ / h], and the supplied sludge liquid flow rate Qw at each air flow rate Qa. The graph of FIG. 5 shows the result of determining the change in the pumping coefficient k when the value is changed from 2 to 10 [m ³ / h]. As shown in FIG. 5, the pumping coefficient k increases as the air flow rate Qa increases, and decreases as the sludge liquid flow rate Qw increases. In the case of the membrane module of the example, the cleaning air flow rate per one is 5 [Nm ³ / h] as a standard value.

The sludge liquid flow rate Qw is related to the MLSS concentration in the membrane separation tank. When the air flow rate Qa and the sludge liquid flow rate Qw are changed as shown in FIG. 5, the amount of filtered water in the membrane module is 0.83 [m ³ / The graph of FIG. 6 shows the results of determining changes in the MLSS concentration [mg / L] in the membrane separation tank and the pumping coefficient with respect to changes in each air flow rate Qa when maintained at h].

In the hollow fiber membrane module of the above example, the upper limit of the MLSS concentration in the membrane separation tank is 12000 mg / L, and if it is more than that, the viscosity of the liquid becomes too high to be mixed, so the sludge liquid flow rate Qw to be supplied is Filtration cannot be continued unless it is 3 [m ³ / h] or more. Conversely, if the sludge liquid flow rate Qw is too high, there is a problem that the air flow rate Qa for that purpose becomes enormous. Sludge liquid flow rate Qw exceeding 10 [m ³ / h] is not necessary and impractical.

When the characteristics of FIGS. 5 and 6 are judged from the above viewpoint, when the air flow rate Qa is set to a large 10 Nm ³ / h with a margin, the pumping coefficient is optimally in the range of 0.5 to 0.8. When the required air flow rate Qa is reduced to 3Nm ³ / h, the pumping coefficient is optimally in the range of 0.2 to 0.5. Based on the above points, the air flow rate Qa is 0.2 to 0.8. It is preferable to define in such a range.

1 is an elevational view showing a schematic configuration of the membrane separation apparatus according to the first embodiment of the present invention in a cross-sectional shape. The elevation view which shows schematic structure of the membrane separator concerning the 2nd Embodiment of this invention with a cross-sectional shape The elevation which shows schematic structure of the membrane separator concerning the 3rd Embodiment of this invention with a cross-sectional shape The top view of the membrane separator concerning the 4th Embodiment of this invention The graph which shows the relationship between the change of air flow rate Qa and sludge liquid flow rate Qw, and a pumping coefficient in the membrane separator in an Example. Graph showing the relationship between MLSS concentration in the membrane separation tank and pumping coefficient based on the results of FIG.

Explanation of symbols

10-13 membrane separator
20 Bioreactor
20C aerobic tank
30 Membrane separation tank
40 Membrane module
41 Filtration membrane
50 Drain pipe
60 Sludge supply pipe
61 Reaction tank side opening
62 Separation tank side opening
63 Extension tube
70 Sludge return pipe
80 Air supply means
81 Air supply port

Claims (3)

A membrane separation apparatus for solid-liquid separation of sludge liquid after biological reaction treatment in a biological reaction tank containing activated sludge liquid,
A membrane separation tank installed separately from the biological reaction tank;
A plurality of membrane modules arranged vertically in the membrane separation tank;
In order to circulate sludge liquid in the biological reaction tank and the membrane separation tank, a sludge liquid supply pipe connecting the membrane separation tank and the biological reaction tank at the lower part,
In order to circulate sludge liquid in the biological reaction tank and the membrane separation tank, a sludge liquid return pipe connecting the membrane separation tank and the biological reaction tank at the upper part,
Air supply means for ejecting air into the membrane separation tank,
The sludge liquid supply pipe has a downstream end portion that penetrates to the inside of the membrane separation tank, extends to the lower part of each of the membrane modules, and opens upward corresponding to the bottom position of each membrane module. And
An air supply port of the air supply means which is installed in the separation tank side opening and jets air toward the membrane module;
In the separation tank side opening of the sludge liquid supply pipe, the lower part of the membrane module is fixed, and an extended cylinder part of the separation tank side opening is formed surrounding the lower outer periphery of the membrane module,
The sludge liquid is fed into the membrane separation tank from the separation tank side opening of the sludge liquid supply pipe by the air ejected from the air supply port, and the membrane cleaning of the membrane module is performed. Membrane separator. The upstream end portion of the sludge liquid supply pipe installed in the bioreactor is open downward and installed in a downward flow part in the circulating flow of sludge in the bioreactor. claim 1 Symbol placement of the membrane separation apparatus. The air flow rate supplied from the air supply port to the membrane separation tank by the air supply means is Qa [Nm ³ / h], the air flow rate is Qw [m ³ / h]. The membrane separation apparatus according to claim 1 or 2 , wherein the pumping coefficient k = 1- [1 ÷ (Qa ÷ Qw + 1)] is defined in a range of 0.2 to 0.8.

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