Water treatment apparatus

Abstract

To provide a water treatment apparatus capable of being installed in a compact space, while preventing unnecessary dissolved oxygen into an oxygen-free tank.SOLUTION: A water treatment apparatus 1 includes: an oxygen-free tank 4 into which raw water flows in; a treatment tank 3 with a plurality of membrane separation units 7 immersed and installed; ; an inflow passage 5 configured to supply treatment-target water from the oxygen-free tank 4 to the treatment tank 3; and a return passage 6 configured to return the treatment-target water from the treatment tank 3 to the oxygen-free tank 4. The membrane separation units 7 are arranged in multiple rows in the treatment tank 3. The return passage 6 is arranged directly below each row of the membrane separation units 7 in a manner extending in a direction along each of the rows. In the return passage 6, portions corresponding to the membrane separation units 7 arranged in each row are covered, and an opening is to receive the treatment-target water is formed at portions corresponding to gaps between the membrane separation units 7.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a water treatment device comprising an anoxic tank into which raw water flows, a treatment tank in which a plurality of membrane separation devices are submergedly installed, an inlet line for supplying water to be treated from the anoxic tank to the treatment tank, and a return line for returning the water to be treated from the treatment tank to the anoxic tank. [Background technology]

[0002] 2. Description of the Related Art Water treatment equipment employing a membrane separation activated sludge process has been attracting attention for purifying organic wastewater such as sewage, livestock wastewater, human waste, and wastewater generated in food factories. Figure 1 shows an example of the configuration of a conventional water treatment system that employs the membrane bioreactor. From the upstream side, an anaerobic tank AN, an anoxic tank AX, a pre-aeration tank PA, and a membrane separation tank MBR are arranged. Raw organic wastewater flows into the anaerobic tank AN and is mixed with activated sludge to become treated water, which is purified as it flows down the anaerobic tank AN, anoxic tank AX, pre-aeration tank PA, and membrane separation tank MBR in that order. Note that the pre-aeration tank PA may also function as an anoxic tank if necessary.

[0003] The anaerobic tank AN undergoes dephosphorization, the anoxic tank AX undergoes denitrification, the pre-aeration tank PA undergoes nitrification (aerobic), and the membrane separation tank MBR undergoes nitrification (aerobic) and membrane separation. Sludge withdrawn from the membrane separation tank MBR is returned to the anaerobic tank AN or anoxic tank AX via the return line RS. As the water to be treated is circulated between the anaerobic tank AN and the membrane separation tank MBR, organic wastewater is purified, and the water to be treated is withdrawn as treated water by the membrane separation unit MS.

[0004] The membrane separation tank MBR is a treatment tank in the shape of a rectangular parallelepiped that is rectangular in plan view and elongated in one direction, and multiple membrane separation devices MS are submerged and installed in a row along the longitudinal direction of the treatment tank. An aeration device is installed below each membrane separation unit MS, and oxygen supplied from the aeration device purifies the membrane surface and aerobic treats the water being treated. Any oxygen that is insufficient during aerobic treatment by the aeration device is supplied from an auxiliary aeration device installed in the pre-aeration tank PA upstream of the membrane separation tank MBR.

[0005] In order to prevent fouling of the membrane separation unit MS, the dissolved oxygen concentration (DO concentration) of the water being treated flowing from the pre-aeration tank PA to the membrane separation tank MBR is often adjusted to 1-2 mg / L, and the aerobic treatment is almost completed in the upstream area of ​​the pre-aeration tank PA and the membrane separation tank MBR, resulting in an excess supply of oxygen in the downstream area of ​​the membrane separation tank MBR. As a result, sludge with a high dissolved oxygen concentration is returned from the downstream side of the membrane separation tank MBR to the anaerobic tank AN or anoxic tank AX, which wastefully brings dissolved oxygen into the anaerobic tank AN or anoxic tank AX.

[0006] In other words, the upstream area of ​​the MBR membrane separation tank where aerobic treatment takes place has a high soluble COD (sCOD) concentration and is exposed to an environment where membrane fouling is more likely to occur than in the downstream area, resulting in uneven membrane fouling in the direction of the flow of the treated water.

[0007] In addition, because treated water is withdrawn from the membrane separation unit MS, the MLSS concentration increases downstream of the membrane separation unit MBR, increasing the risk of inter-membrane clogging. Therefore, the amount of air diffused from the air diffuser installed at the bottom of the membrane separation unit MS must be set higher downstream of the membrane separation unit MBR.

[0008] FIG. 2(a) illustrates the cross-sectional structure of a membrane separation tank MBR in which a membrane separation apparatus MS is installed. The membrane separation apparatus MS is equipped with two membrane cases MC, one above the other, and an aeration device AD ​​installed below the membrane case MC. The membrane surface of the membrane case MC is purified by the upward flow generated in the water to be treated by the aeration from the aeration device AD, and a swirling flow of the water to be treated is formed so that the water flows downward from the top to both sides of the membrane separation apparatus MS. Therefore, as shown in FIG. 2(b) and (c), the dissolved oxygen concentration of the water to be treated filled in the membrane separation tank MBR is high on the water surface side and low on the bottom side. For the convenience of calculating the transmembrane pressure difference, it is necessary to keep the water level constant, and the overflow water from the membrane separation tank MBR is stored in a terminal water tank and returned as returned sludge using a pump, which is one of the reasons why sludge with a high dissolved oxygen (DO) concentration is returned to the anaerobic tank AN or anoxic tank AX.

[0009] Patent Document 1 proposes a wastewater treatment facility that can ensure a stable upward flow even when a membrane separation device is installed in a compact space and that can reduce operating costs. The wastewater treatment facility comprises an anoxic tank where denitrification treatment is performed, an aerobic tank where nitrification treatment is performed, and a number of membrane separation devices that are immersed in the water to be treated that has been nitrified and perform a solid-liquid separation treatment to obtain permeate from the water to be treated, with troughs extending toward the anoxic tank being disposed in the space above each membrane separation device, and the wastewater treatment facility is configured so that the concentrated water after solid-liquid separation treatment overflows into the troughs by the upward flow of the water to be treated caused by aeration from an aeration mechanism provided in the membrane separation devices, and is returned to the anoxic tank.

[0010] According to this wastewater treatment facility, the water to be treated flows from the bottom to the top of the membrane separation device due to the air lift effect caused by the air bubbles released from the air diffusion mechanism, that is, the concentrated water after membrane filtration flows into a trough provided above the membrane separation device and is returned to the anoxic tank via the trough for denitrification. Therefore, there is no need to provide a separate pump mechanism for returning the concentrated water to the anoxic tank, which reduces the operating costs for power. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2018-43214 A Summary of the Invention [Problem to be solved by the invention]

[0012] However, even in the wastewater treatment equipment described in Patent Document 1, sludge with a high dissolved oxygen concentration near the water surface of the membrane separation device is returned to the anoxic tank via the trough, resulting in an inefficient configuration that wastefully brings in dissolved oxygen.

[0013] In view of the above-mentioned problems, an object of the present invention is to provide a water treatment device that can be installed in a compact space and can suppress the introduction of unnecessary dissolved oxygen into the anoxic tank. [Means for solving the problem]

[0014] In order to achieve the above-mentioned object, a first characteristic configuration of a sewage treatment facility according to the present invention is a water treatment device comprising an anoxic tank into which raw water flows, a treatment tank in which a plurality of membrane separation devices are submergedly installed, an inlet channel for supplying water to be treated from the anoxic tank to the treatment tank, and a return channel for returning the water to be treated from the treatment tank to the anoxic tank, wherein the membrane separation devices are arranged in a plurality of rows in the treatment tank, the return channels are installed directly below each row of the membrane separation devices so as to extend in a direction along each row, the return channels are covered in the portions corresponding to the membrane separation devices arranged in each row, and openings for receiving the water to be treated are formed in the portions corresponding to the gaps between the membrane separation devices.

[0015] By arranging multiple membrane separation devices in multiple rows in the treatment tank, it is not necessary to use a treatment tank with a rectangular parallelepiped shape that is elongated in one direction, and a compact treatment tank can be realized. In each membrane separation device, the water to be treated is separated into solid and liquid and the treated water is extracted, and the membrane surface of the separation membrane is washed by the upward flow of the water to be treated caused by aeration from an aeration device installed below the separation membrane. The upward flow then flows down from the top of the membrane separation device between each row as a downward flow.

[0016] In other words, the water to be treated rises inside the membrane separation device, and a swirling flow that descends between the rows on both sides of the membrane separation device is generated. In the descending flow area, oxygen consumption due to aerobic treatment and respiration by microorganisms in the activated sludge progresses, and if there is a shortage of oxygen there, oxygen is supplied from the auxiliary air diffuser 8, so that the dissolved oxygen concentration at the bottom of the treatment tank becomes extremely low. Directly below each row of the membrane separation device, return paths are installed so as to extend in the direction along each row, and the water to be treated, which has a low dissolved oxygen concentration, is returned to the anoxic tank as returned sludge via the return paths, so that denitrification, an anoxic process, proceeds efficiently in the anoxic tank.

[0017] If the water to be treated flows out from the portion of the groove corresponding to the membrane separation device, the upward flow of the water to be treated is hindered even with the aeration from the aeration device, so the cleaning process of the membrane surface of the separation membrane does not progress, and the risk of sludge accumulation on the membrane surface increases. Therefore, by covering the portions corresponding to the membrane separation devices arranged in each row and forming openings for receiving the water to be treated in the portions corresponding to the gaps between the membrane separation devices, it becomes possible to return the water to be treated, which has a low dissolved oxygen concentration, to the anoxic tank as returned sludge without hindering the cleaning process of the membrane surface of the separation membrane.

[0018] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the return path is composed of a groove formed in the floor of the treatment tank, and a cover body is installed in the groove at a position corresponding to the membrane separation device arranged in each row.

[0019] By forming grooves in the floor of the treatment tank so as to correspond directly below each row of membrane separation devices, and having the grooves function as return paths, and by installing a lid body in the portion of the groove that corresponds to the membrane separation device, the treatment tank can be configured compactly.

[0020] The third characteristic configuration is, in addition to the first characteristic configuration described above, that the return path is composed of a gutter installed on the floor of the treatment tank so as to extend in a direction along each row directly below the membrane separation device, and a cover body is installed on the gutter at a position corresponding to the membrane separation device arranged in each row.

[0021] In cases where it is difficult to form grooves on the floor of the treatment tank, gutters can be installed on the floor of the treatment tank to function as an alternative to the grooves. In this case, too, it is preferable to install covers on the gutters at locations corresponding to the membrane separation devices arranged in each row.

[0022] The fourth characteristic configuration is that, in addition to the first characteristic configuration described above, the return path is composed of a pipe body installed on the floor of the treatment tank so as to extend in a direction along each row directly below the membrane separation device, and openings are formed in the pipe body at locations corresponding to the gaps between the membrane separation devices arranged in each row.

[0023] Instead of using a gutter, a tube is installed on the floor of the treatment tank and openings are formed in the areas corresponding to the gaps between the membrane separation devices arranged in each row, making it possible to return the treated water with a low dissolved oxygen concentration to the anoxic tank as return sludge without interfering with the cleaning process of the separation membrane surface. Effect of the Invention

[0024] As described above, according to the present invention, it is possible to provide a water treatment device that can be installed in a compact space and that can prevent unnecessary dissolved oxygen from being brought into the anoxic tank. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a plan view of a conventional water treatment device; [Diagram 2] (a) is an explanatory diagram of the main part of the cross section taken along line I-I in Figure 1, (b) is an explanatory diagram of the DO concentration distribution inside the membrane shunt device shown in (a), and (c) is an explanatory diagram of the DO concentration distribution inside the treatment tank shown in (a). [Diagram 3] FIG. 2A is a plan view of a water treatment device according to the present invention, and FIG. 2B is a cross-sectional view taken along line II-II of FIG. [Figure 4] Illustration of membrane separation device [Diagram 5] Diagram of membrane element [Figure 6] 1A to 1D are explanatory diagrams showing the configuration of the inlet passage. [Figure 7] Return path diagram [Figure 8] FIG. 3A is a plan view illustrating another embodiment of a water treatment device according to the present invention; FIG. 3B is a cross-sectional view taken along line III-III of FIG. [Figure 9]FIG. 4A is a plan view illustrating another embodiment of a water treatment device according to the present invention; FIG. 4B is a cross-sectional view taken along line IV-IV of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The water treatment device according to the present invention will be described below. The water treatment device is a water treatment device that purifies raw sewage by using a membrane separation activated sludge method. The water treatment device can purify organic wastewater such as livestock wastewater, human waste, and wastewater from food factories, in addition to sewage.

[0027] As shown in Figures 3(a) and (b), the water treatment device 1 is equipped with a treatment tank 3 for performing nitrification treatment and membrane separation treatment of ammonia nitrogen contained in raw water, anoxic tanks 4 arranged on either side of the treatment tank 3 for performing denitrification treatment, an inlet line 5 for supplying the water to be treated from the anoxic tank 4 to the treatment tank 3, and a return line 6 for returning the water to be treated from the treatment tank 3 to the anoxic tank 4.

[0028] In the treatment tank 3, a plurality of membrane separation devices 7 are arranged in multiple rows and submerged, and auxiliary air diffusers 8 are installed between the rows of membrane separation devices 7 so as to extend in a direction along each row. In this example, the plurality of membrane separation devices 7 are arranged in three rows between a pair of opposing walls W that are rectangular in plan view and that partition the treatment tank 3, and each row has seven membrane separation devices 7 arranged at equal intervals. Anoxic tanks 4 are arranged on either side of the pair of opposing walls W.

[0029] 4 shows an example of a membrane separation device 7. The membrane separation device 7 has 100 plate-like membrane elements 71 arranged vertically in two stages at regular intervals of about 6 mm to 10 mm (8 mm in this embodiment) inside a membrane case 70 that is open at the top and bottom, and further has an air diffuser 7A below the membrane case 70.

[0030] The air diffuser 7A includes an air diffuser pipe 72 having a plurality of air diffuser holes formed therein, and is connected to an air supply source such as a blower B or a compressor installed outside the tank via an air diffuser header 73 connected to the air diffuser pipe 72. In this embodiment, the blower B is used as the air supply source.

[0031] The membrane element 71 is connected to a water collection pipe 74 via a tube 75, and a pump P1 serving as a suction mechanism installed outside the tank is also connected via the water collection pipe 74, so that the water to be treated in the treatment tank 3 is suction-filtered so as to pass through the membrane surface of the membrane element 71.

[0032] As shown in FIG. 5, membrane element 71 has separation membranes 78 arranged on both the front and back sides of a resin membrane support 76 measuring 1000 mm in length and 490 mm in width, with spacers 77 interposed between them, and peripheral edge portion 78E of separation membrane 78 is bonded to membrane support 76 by ultrasonic or thermal welding, or by using an adhesive or the like.

[0033] The separation membrane 78 is a microporous membrane with an average pore size of about 0.2 μm, and is an organic filtration membrane in which a nonwoven fabric is coated and impregnated with a porous resin. Note that the membrane element 71 is not limited to this configuration, and the separation membrane 78 may be arranged so as to be wrapped around both the front and back sides of the membrane support 76, and the ends of the separation membrane 78 may be bonded or welded.

[0034] A plurality of grooves 76G, each about 2 mm deep and 2 mm wide, are formed in the longitudinal direction on the surface of the membrane support 76, and a horizontal groove 76H is formed at the upper end thereof, connecting the grooves 76G. The horizontal grooves 76H formed on both the front and back surfaces are connected via communication holes 71H, and are connected to a nozzle 71N formed on the upper edge of the membrane support 76.

[0035] Each nozzle 71N is connected to a water collection pipe 74 via a tube 75, and a pump P1 serving as a suction mechanism is connected to the water collection pipe 74 so that the permeate sucked up by the pump P1 is transported to the treatment water tank as treated water.

[0036] By operating the air diffuser 7A of such a membrane separation apparatus 7, an upward flow of the water to be treated is formed in the gaps of the membrane element 71 from the bottom to the top, preventing fouling substances and impurities from accumulating on the membrane surface of the separation membrane 78, and by operating the suction mechanism, permeate water can be obtained by passing the water to be treated through the separation membrane 78.

[0037] 3(a) and (b), the explanation will be continued. The inflow channel 5 is composed of two pipes 50 extending in a direction along each row between the rows of the membrane separation devices 7, and the end of each pipe 50 is arranged so as to extend into each anoxic tank 4. The pipes 50 are arranged in a horizontal position near the liquid level of the water to be treated filled in the treatment tank 3, specifically, slightly below the liquid level. Note that the pipes 50 need only be located near the liquid level, and may also be located slightly above the liquid level.

[0038] In FIG. 6(a), the pipe 50 is shown in a side view on the left, and a cross section of the pipe 50 is shown on the right. A plurality of openings 5H are formed in each pipe 50 so as to be distributed in the axial direction so that the water to be treated is distributed in the extension direction of each pipe 50 and supplied to the treatment tank 3. It is preferable that the diameter and interval of the openings 5H formed in the axial direction are adjusted so that the water to be treated flowing from each anoxic tank 4 into the treatment tank 3 through the pipe 50 is evenly supplied in the extension direction of each pipe 50. For example, the diameter of the central part where the inflow pressure of the water to be treated is high may be formed smaller than the diameter of the end part, or the interval on the end part may be formed smaller than the interval on the central part.

[0039] As shown in FIG. 3(b), an upward flow generated in the water to be treated by the air diffused from the air diffuser 7A provided at the bottom of the membrane separation device 7 rises along the gaps of the membrane element 71 provided inside the membrane case 70, and the membrane surface of the separation membrane 78 (see FIG. 5) is washed. After that, the upward flow descends between the rows from the top of the membrane separation device 7. That is, the water to be treated rises inside the membrane separation device 7, and a swirling flow descends between the rows on both sides of the membrane separation device 7. The water to be treated flowing in from the inlet 5 descends toward the auxiliary air diffuser 8 along the downward flow generated between the rows, so that aerobic treatment progresses efficiently. The particle size of the air bubbles discharged from the auxiliary air diffuser 8 is much smaller than that of the air bubbles discharged from the air diffuser 7A provided at the bottom of the membrane separation device 7, and the amount of air diffused is set to a small value, so that there is a sufficient opportunity for contact with the downward flow of the water to be treated.

[0040] The return path 6 is installed directly below each row of membrane separation devices 7 so as to extend in a direction along each row. An example of the return path 6 is shown in Fig. 7. The return path 6 is composed of grooves 60 formed in the floor of the treatment tank 3, and the portions of the grooves 60 corresponding to the membrane separation devices 7 arranged in each row are covered with lids 61 that prevent the water to be treated from flowing into the grooves 60 so that the water to be treated, which becomes a swirling flow, is guided from below to above the membrane separation devices 7, and openings 62 are formed so that the water to be treated flows into the grooves 60 from portions corresponding to the gaps between the membrane separation devices 7.

[0041] The water to be treated that flows into the groove 60 from the opening 62 is returned to each anoxic tank 4 adjacent to each other with the opposing wall W therebetween.

[0042] By arranging a plurality of membrane separation devices 7 in a plurality of rows in the treatment tank 3, it is not necessary to form the treatment tank in a rectangular parallelepiped shape that is elongated in one direction, and a compact treatment tank 3 can be realized. Then, by installing auxiliary aeration devices 8 at the bottom of the treatment tank 3 so as to extend between the rows of membrane separation devices 7 in a direction along each row, and by installing inflow channels 5 so as to supply the water to be treated in a dispersed manner between the rows of membrane separation devices 7 in a direction along each row, aerobically treated water is uniformly treated between the rows of membrane separation devices 7.

[0043] The water to be treated is subjected to solid-liquid separation by the membrane separation device 7 located nearby and withdrawn as treated water. In other words, the water is dispersed and uniformly treated in the treatment tank 3, and the aerobic treatment and membrane separation treatment are performed, which effectively suppresses the influence on the membrane separation device caused by the gradient distribution of the dissolved oxygen concentration and the gradient distribution of the MLSS concentration along the flow direction of the water to be treated that occurs when a treatment tank having a rectangular parallelepiped shape that is elongated in one direction is used.

[0044] Furthermore, the water to be treated at the bottom of the treatment tank 3, which has a low dissolved oxygen concentration (DO concentration), is returned to the anoxic tank 4, and the water to be treated at the upper layer of the treatment tank 3, which has a high dissolved oxygen concentration (DO concentration), comes into efficient contact with the water to be treated flowing in from the inlet 5.

[0045] As described above, in each membrane separation device 7, the water to be treated is separated into solid and liquid and is extracted as treated water, and the membrane surface of the separation membrane 78 is washed by the upward flow of the water to be treated caused by aeration from the aeration device 7A provided below the separation membrane 78. The upward flow then becomes a downward flow and flows down from the top of the membrane separation device 7 between each row.

[0046] In other words, the water to be treated rises inside the membrane separation device, and a swirling flow that descends between the rows on both sides of the membrane separation device is generated. In the descending flow area, oxygen consumption due to aerobic treatment and respiration by microorganisms in the activated sludge progresses, and if there is a shortage of oxygen there, oxygen is supplied from the auxiliary air diffuser 8, so that the dissolved oxygen concentration at the bottom of the treatment tank 3 becomes extremely low. Directly below each row of the membrane separation device 7, return paths 6 are installed so as to extend in the direction along each row, and the water to be treated with a low dissolved oxygen concentration is returned to the anoxic tank 4 as returned sludge via the return paths 6, so that denitrification, an anaerobic process, progresses efficiently in the anoxic tank 4.

[0047] If the water to be treated flows out from the portion of the groove corresponding to the membrane separation device 7, the upward flow of the water to be treated is hindered even with aeration from the aeration device 7A, so that the cleaning process of the membrane surface of the separation membrane 78 does not progress, and the risk of sludge accumulation on the membrane surface increases. Therefore, by covering the portions corresponding to the membrane separation devices 7 arranged in each row and forming openings for receiving the water to be treated in the portions corresponding to the gaps between the membrane separation devices 7, it becomes possible to return the water to be treated, which has a low dissolved oxygen concentration, to the anoxic tank 4 as returned sludge without hindering the cleaning process of the membrane surface of the separation membrane 78.

[0048] By providing a pump mechanism in either the inflow path 5 through which the water to be treated flows from the anoxic tank 4 to the treatment tank 3, or the return path 6 through which the water to be treated is returned from the treatment tank 3 to the anoxic tank 4, the water to be treated can be circulated stably between the anoxic tank 4 and the treatment tank 3. In addition, by separately installing an excess sludge withdrawal path for withdrawing excess sludge from the treatment tank 3, the MLSS concentration in the treatment tank 3 can be kept constant.

[0049] Another embodiment of the water treatment device 1 will be described below. In the above-described embodiment, an anoxic tank 4 is disposed on either side of a pair of opposing walls W of the treatment tank 3, and raw water flows into the anoxic tank 4. However, an anaerobic tank for removing phosphorus may be provided on the opposite side of the treatment tank 3 across the anoxic tank 4, and raw water may flow into the anaerobic tank. In this case, a sludge return path may be further provided between the anaerobic tank and the anoxic tank 4. Needless to say, the configuration in which an anaerobic tank is provided adjacent to the anoxic tank 4 can also be applied to other embodiments of the water treatment device 1 described later.

[0050] In the above embodiment, the anoxic tanks 4 are arranged on either side of a pair of opposing walls W of the treatment tank 3, but an embodiment in which one anoxic tank 4 is arranged on either side of one of the pair of opposing walls W of the treatment tank 3 may also be adopted. Also, an anaerobic tank may be provided on the opposite side of the treatment tank 3 across the anoxic tank 4. In this case, the water to be treated flows through the inlet line 5 and the return line 6 in only one direction.

[0051] In the above-described embodiment, a configuration has been described in which a plurality of membrane separation devices 7 are arranged in a row between a pair of opposing walls W that are rectangular in plan view and that separate the treatment tank 3, a plurality of membrane separation devices 7 are arranged at equal intervals in each row, and anoxic tanks 4 are further arranged on either side of the pair of opposing walls W. However, the present invention is not limited to such an arrangement. For example, as shown in Figures 8(a) and (b), a plurality of membrane separation devices 7 may be arranged in a row between a pair of opposing walls W, with a plurality of membrane separation devices 7 arranged at equal intervals in each row, and the anoxic tank 4 may be disposed across an opposing wall W' that is different from the pair of opposing walls W.

[0052] In this embodiment, the water to be treated from the anoxic tank 4 flows into the treatment tank 3 via a communication pipe 53 that connects the multiple pipes 50 arranged on the pair of opposing walls W, and the returned sludge is returned from the treatment tank 3 to the anoxic tank 4 via a communication pipe 63 that connects the multiple return paths 6 arranged on the pair of opposing walls W. In this example, a pump P for supplying the water to be treated is installed in the communication pipe 53.

[0053] Furthermore, as shown in Figures 9(a) and (b), in addition to the water treatment device 1 shown in Figures 3(a) and (b), an auxiliary aeration device 8 may be installed between the membrane separation device 7 and the side wall W'' of the treatment tank 3 so as to extend in a direction along each row, and the inflow conduit 5 may be installed between the membrane separation device 7 and the side wall W'' of the treatment tank 3 so as to supply the water to be treated in a dispersed manner in a direction along each row. By configuring in this manner, aerobic treatment is performed uniformly not only between the rows of membrane separation devices but also between the membrane separation devices and the side wall of the treatment tank, and aerobic treatment is performed more uniformly throughout the treatment tank as a whole.

[0054] 9(a) and 9(b) may be combined with the water treatment device 1 shown in Fig. 8(a) and 8(b). That is, the auxiliary air diffuser 8 may be installed between the membrane separation device 7 and the side wall W' of the treatment tank 3 so as to extend in a direction along each row, and the inflow channel 5 may be installed between the membrane separation device 7 and the side wall W' of the treatment tank 3 so as to supply the water to be treated in a dispersed manner in a direction along each row.

[0055] 6(b) to (d) show various aspects of the inflow channel 5. In FIG. In FIG. 6(b), the pipe 50 is shown in a side view on the left, and the cross section of the pipe 50 is shown on the right. The pipe 50 constituting the inflow passage 5 has a slit formed along the axial direction, and the slit functions as an opening 5H. In this example, one slit is formed in the longitudinal direction of the pipe 50 at a position inclined at a predetermined angle θ to the left and right with respect to a vertical line passing through the center of the pipe 50. The value of the predetermined angle θ is not particularly limited, and may be set appropriately. The predetermined angle θ may be set to 0°, and one slit may be formed directly below. These points are the same as in FIG. 6(a).

[0056] The slit may be divided into a plurality of slits along the longitudinal direction of the pipe 50. It is preferable that the width and length of the slit are adjusted so that the water to be treated flowing from each anoxic tank 4 through the pipe 50 into the treatment tank 3 is evenly supplied in the extending direction of each pipe 50. For example, the slit width at the center where the inflow pressure of the water to be treated is high can be made narrower than the slit width at the end. In addition, when the anoxic tank 4 is disposed on only one of the opposing walls W of the treatment tank 3, the inflow pressure of the water to be treated is high at the pipe end side opposite to the pipe end of the pipe 50 located on the anoxic tank 4 side, so the slit may be formed so that the slit width gradually narrows toward the opposite pipe end side.

[0057] Fig. 6(c) shows a gutter-shaped inflow channel 5. The bottom of the inflow channel 5 is located slightly lower than the water level in the anoxic tank 4, and notches 5N are formed on the upper edge so that the water to be treated that flows into the gutter in the anoxic tank 4 overflows into the treatment tank 3. As in Figs. 6(a) and 6(b), the depth and intervals of the notches 5N are preferably adjusted so that the water to be treated that flows from the anoxic tank 4 through the inflow channel 5 into the treatment tank 3 is supplied evenly in the extension direction of the inflow channel 5.

[0058] 6(a)-(c) show an example in which the inflow passage 5 is formed of one pipe 50 or gutter, but as shown in FIG. 6(d), the inflow passage 5 may be formed of a plurality of pipes 50 arranged so that the open ends are dispersed along the extending direction of the inflow passage 5. The inflow passage 5 is formed by a plurality of pipes 50 from which the water to be treated flows in from one open end 50A and flows out from the other open end 50B into the treatment tank 3, and the positions of the other open ends 50B of the pipes 50 may be made different so that the other open ends 50B of the pipes 50 are dispersed along the extending direction of the inflow passage 5. This is suitable for use when the anoxic tank 4 is disposed only on one side of a pair of opposing walls W of the treatment tank 3.

[0059] In the above-mentioned embodiment, the return path 6 is configured as a groove 60 formed on the floor of the treatment tank 3. However, the return path 6 may be configured as a gutter installed on the floor of the treatment tank 3 so as to extend in a direction along each row immediately below the membrane separation devices 7, and a cover may be installed on the gutter at a position corresponding to the membrane separation devices 7 arranged in each row. Even if it is difficult to form a groove in the bottom of the treatment tank 3 made of a concrete structure, the return path 6 can be configured by installing a gutter on the floor of the treatment tank 3 immediately below the membrane separation devices 7.

[0060] In addition, the return path 6 may be constructed of a pipe installed on the floor of the treatment tank 3 so as to extend in a direction along each row directly below the membrane separation devices 7, and openings through which the return sludge flows may be formed in the pipe at positions corresponding to the gaps between the membrane separation devices 7 arranged in each row.

[0061] The above-described embodiment is an explanation of one aspect of the present invention, and the present invention is not limited to this description. It goes without saying that the specific configuration of each part can be appropriately modified and designed within the scope of the effect of the present invention. [Explanation of symbols]

[0062] 1: Water treatment equipment 3: Treatment tank 4: Anoxic tank 5: Inflow channel 6: Return route 7: Membrane separation device 8: Auxiliary air diffuser

Claims

1. A water treatment device comprising an anoxic tank into which raw water flows, a treatment tank in which a plurality of membrane separation devices are submerged, an inlet line for supplying water to be treated from the anoxic tank to the treatment tank, and a return line for returning the water to be treated from the treatment tank to the anoxic tank, The membrane separation devices are arranged in a plurality of rows in the treatment tank, The return line is installed immediately below each row of the membrane separation device so as to extend in a direction along each row, The return path is covered in the areas corresponding to the membrane separation devices arranged in each row, and an opening for receiving the water to be treated is formed in the areas corresponding to the gaps between the membrane separation devices.

2. The water treatment facility according to claim 1, wherein the return path is constituted by a groove formed in the floor of the treatment tank, and a cover is installed in the groove at a position corresponding to the membrane separation device arranged in each row.

3. The water treatment facility described in claim 1, wherein the return path is composed of a gutter installed on the floor of the treatment tank so as to extend in a direction along each row directly below the membrane separation device, and a cover is installed on the gutter at a position corresponding to the membrane separation device arranged in each row.

4. The water treatment facility according to claim 1, wherein the return path is composed of a pipe installed on the floor of the treatment tank so as to extend in a direction along each row directly below the membrane separation device, and the pipe has openings formed in locations corresponding to the gaps between the membrane separation devices arranged in each row.

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