Method for upgrading water treatment facilities and membrane separation apparatus

Abstract

To provide a method for renewing a water treatment facility capable of maintaining good treatment efficiency with membrane units even when the number of immersion type membrane units is reduced.SOLUTION: A method of renewing a water treatment facility 1 having a plurality of treatment tanks 7-9 equipped with a first air diffuser 23 includes: a first process of installing an immersion type membrane unit 31 in at least one treatment tank 8 other than the renewal target, subjecting a part of the liquid 2 to be treated supplied to the treatment tank 8 other than the renewal target to solid-liquid separation by the membrane unit 31 and discharging it to the outside of the treatment tank 8, and discharging the remainder of the liquid 2 to be treated to the outside of the treatment tank 8 after diffusing air by a first air diffuser 23; a second process of renewing the treatment tank 7 to be renewed while the first air diffuser 23 of the treatment tank 7 to be renewed is stopped; and a third process of removing the membrane unit 31 from the treatment tank 8 other than the treatment tank to be renewed after the renewal. The first process involves solid-liquid separation by surrounding the lateral perimeter of the membrane unit 31 with an enclosure 32, and the second process is carried out while the first process is carried out.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an update method and a membrane separation device when updating a water treatment facility having a plurality of treatment tanks equipped with aeration devices.

Background Art

[0002] Conventionally, as a method for updating this type of water treatment facility, for example, as shown in FIG. 12, a plurality of floating immersion-type membrane separation devices 126 are introduced into a predetermined aerobic tank 122 of any one of a plurality of existing aerobic tanks 122 to 124 equipped with an existing aeration device 121, and the predetermined aerobic tank 122 is operated as an aerobic tank using the floating immersion-type membrane separation device 126. In a first step, the liquid to be treated 127 stored in the other aerobic tanks 123 and 124 into which the floating immersion-type membrane separation device 126 has not been introduced is discharged outside the aerobic tanks 123 and 124, and after the other empty aerobic tanks 123 and 124 are updated, the liquid to be treated 127 is supplied to the other aerobic tanks 123 and 124 to operate the other aerobic tanks 123 and 124. In a second step, and a third step of removing the floating immersion-type membrane separation device 126 from the predetermined aerobic tank 122 into which the floating immersion-type membrane separation device 126 has been introduced in the first step. Some methods have these steps.

[0003] In addition, the floating immersion-type membrane separation device 126 is equipped with floating means and floats in the liquid to be treated 127, and the liquid to be treated 127 is solid-liquid separated by a membrane unit.

[0004] The method for updating a water treatment facility as described above is described in, for example, Patent Document 1 below.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the conventional configuration described above, as shown in Figure 12, the entire volume of the liquid to be treated 127 supplied to a predetermined aerobic tank 122 is subjected to membrane separation treatment by an immersion-type membrane separator 126 and discharged to the outside of the aerobic tank 122, which increases the number of immersion-type membrane separators 126. Consequently, the number of membrane units also increases, leading to problems such as increased initial costs and running costs. Furthermore, the power required for the membrane separation treatment also increases, making it difficult to secure a power supply.

[0007] Furthermore, as described in Patent Document 1 above, if the membrane separation device is to be used continuously as the main facility after modification, the increase in the number of membrane units is a necessary investment to reach the final form and therefore does not pose a particular problem. However, if a treatment method other than membrane bioreactor (MBR) is adopted as the treatment method after the upgrade, it is desirable to minimize the number of membrane units used.

[0008] The present invention aims to provide a method for updating a water treatment facility and a membrane separation apparatus that can maintain good treatment efficiency by membrane units even when the number of immersion-type membrane units is reduced. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides a method for updating a water treatment facility having a plurality of treatment tanks equipped with a first aeration device, A first step involves installing an immersion-type membrane unit in at least one treatment tank other than the one to be replaced, separating a portion of the liquid to be treated supplied to the treatment tank other than the one to be replaced into solid and liquid by the membrane unit and discharging it to the outside of the treatment tank, and then discharging the remaining liquid to be treated using a first aeration device before discharging it to the outside of the treatment tank. With the first aeration device of the treatment tank to be replaced stopped, the second step is to replace the treatment tank to be replaced, The process includes a third step of removing membrane units from processing tanks other than those to be replaced after the update. In the first step, A casing whose lower end is submerged below the liquid surface in the processing tank and whose upper end protrudes above the liquid surface surrounds the side of the membrane unit. Surround it and separate the solid and liquid, The second step is carried out while the first step is being carried out.

[0010] According to this, in the first step, a portion of the liquid to be treated supplied to the treatment tanks other than the one to be replaced is separated into solid and liquid by a membrane unit and discharged outside the treatment tank, while the remaining liquid to be treated is aerated by a first aeration device and then discharged outside the treatment tank. Therefore, the number of membrane units can be reduced compared to the case where the entire amount of liquid to be treated supplied to the treatment tanks other than the one to be replaced is separated into solid and liquid by a membrane unit and discharged outside the treatment tank.

[0011] Furthermore, in the first step, the membrane unit is surrounded by an enclosure to perform solid-liquid separation. As a result, the liquid to be treated inside the enclosure is concentrated, and the concentration of suspended solids in the liquid to be treated inside the enclosure becomes higher than the concentration of suspended solids in the liquid to be treated outside the enclosure. This allows the concentration of suspended solids in the liquid to be treated inside the enclosure to be raised to a concentration suitable for membrane separation, thereby maintaining good processing efficiency by the membrane unit.

[0012] The method for updating a water treatment facility in the second invention involves, in the first step, performing aeration using a first aeration device of a treatment tank other than the one to be updated, while simultaneously separating the liquid to be treated using a membrane unit.

[0013] According to this, when the treatment tank to be replaced is being replaced in the second step, it is possible to prevent a temporary decrease in the treatment capacity of the water treatment facility.

[0015] This 3 The invention relates to a method for updating a water treatment facility, which is provided with a communication section below the liquid surface that connects the inside and outside of the enclosure.

[0016] This 4 The invention relates to a method for updating a water treatment facility, which includes a discharge device that discharges the liquid to be treated from inside the enclosure to the outside.

[0017] According to this, by discharging the liquid to be treated inside the enclosure through the discharge device to the outside, the liquid to be treated outside the enclosure flows into the inside of the enclosure through the communication part. Therefore, the concentration of suspended substances in the liquid to be treated inside the enclosure can be adjusted to a concentration suitable for membrane separation treatment.

[0018] In this 5 The method for renovating a water treatment facility in this invention is to adjust the MLSS concentration of the liquid to be treated inside the enclosure using a discharge device.

[0019] According to this, the MLSS concentration of the liquid to be treated inside the enclosure can be maintained at a concentration suitable for membrane separation activated sludge treatment.

[0020] In this 6 In the method for renovating a water treatment facility in this invention, the membrane unit has a membrane element and a second air diffuser that generates a swirling flow that swirls in the vertical direction along the membrane element. The enclosure has a peripheral wall that surrounds the lateral periphery of the membrane unit and a bottom wall that is provided at the lower part of the peripheral wall and covers the lower part of the membrane unit. The bottom wall is located above the first air diffuser of the treatment tank.

[0021] According to this, by operating the second air diffuser to perform air diffusion, a swirling flow is generated along the membrane element inside the enclosure, and the surface of the membrane element is washed.

[0022] At this time, since the lower part of the membrane unit is covered by the bottom wall of the enclosure, when the first air diffuser of the treatment tank is operated to perform air diffusion, it is possible to suppress a large amount of bubbles released from the first air diffuser from entering the inside of the enclosure from below.

[0023] Thereby, it is possible to prevent problems such as a large amount of bubbles released from the first air diffuser entering the inside of the enclosure and disturbing the smooth flow of the swirling flow, and it is possible to maintain good cleaning efficiency of the membrane element.

[0024] In this 7The invention relates to a method for updating a water treatment facility, which includes a fourth step of activating the first aeration device of the updated treatment tank to restart the operation of the updated treatment tank. The process involves carrying out the second step while simultaneously performing the first step, and then performing the third and fourth steps either simultaneously or in a different order of time.

[0025] This 8 The invention relates to a membrane separation apparatus comprising a membrane unit and an enclosure used in the water treatment facility renewal method described in the first invention above, The membrane unit and the enclosure are provided on the support frame. The support frame has a submerged portion that is submerged below the liquid surface in the processing tank and an exposed portion that is exposed above the liquid surface. The exposed portion of the support frame body has a supported portion that is supported by the processing tank. A floating element that generates buoyancy is provided on the support frame.

[0026] According to this, in the first step, when the membrane unit is installed in the processing tank, the supported portion of the support frame of the membrane separation device is supported by the processing tank. In this state, buoyancy is generated by the floats provided on the support frame, so the load (self-weight) of the membrane separation device acting on the processing tank via the supported portion of the support frame is reduced by the amount of buoyancy. As a result, reinforcement work on the processing tank can be made unnecessary or significantly reduced.

[0027] This 9 The invention comprises a membrane unit that separates the liquid to be treated from solid to liquid while immersed in the liquid to be treated in a treatment tank, and a support frame that supports the membrane unit. body A membrane separation apparatus having, The support frame has a submerged portion that is submerged below the liquid surface in the processing tank and an exposed portion that is exposed above the liquid surface. The exposed portion of the support frame body has a supported portion that is supported by the processing tank. The support frame is provided with a floating body that generates buoyancy and an enclosure that surrounds the sides of the membrane unit. The enclosure is designed so that its lower end is submerged below the liquid level in the treatment tank, and its upper end protrudes above the liquid level. [Effects of the Invention]

[0028] As described above, according to the present invention, the number of membrane units can be reduced in the first step. Furthermore, the concentration of suspended solids in the liquid to be treated inside the enclosure can be increased to a concentration suitable for membrane separation treatment, and the processing efficiency of the membrane units can be maintained well. [Brief explanation of the drawing]

[0029] [Figure 1] This is a plan view of a water treatment facility according to the first embodiment of the present invention. [Figure 2] This is a view from the direction of arrow XX in Figure 1. [Figure 3] This is a diagram of a membrane separation device used when upgrading water treatment facilities. [Figure 4] This is a floor plan illustrating the method for updating the water treatment facility. [Figure 5] This is a view from the direction of arrow XX in Figure 4. [Figure 6] This diagram shows the swirling flow generated inside the enclosure of a membrane separator when upgrading a water treatment facility. [Figure 7] This is a diagram of a membrane separation device used when upgrading a water treatment facility according to a second embodiment of the present invention. [Figure 8] This is a diagram of a membrane separation device used when upgrading a water treatment facility according to a third embodiment of the present invention. [Figure 9] This is a diagram of a membrane separation device used when upgrading a water treatment facility according to a fourth embodiment of the present invention. [Figure 10] This is a plan view of a membrane separation device used when upgrading a water treatment facility according to a fifth embodiment of the present invention. [Figure 11] This is a diagram of a membrane separation device used when upgrading a water treatment facility according to a sixth embodiment of the present invention. [Figure 12] This is a floor plan illustrating the method for upgrading conventional water treatment facilities. [Modes for carrying out the invention]

[0030] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0031] (First Embodiment) In the first embodiment, as shown in Figures 1 and 2, 1 is an existing water treatment facility that biologically treats the water to be treated 2 (raw water), such as sewage or industrial wastewater, by the standard activated sludge method.

[0032] The water treatment facility 1 has several existing aerobic tanks 7-9 (an example of treatment tanks) arranged in parallel (for example, three in Figure 1), a primary sedimentation tank 10 located upstream of the aerobic tanks 7-9, a final sedimentation tank 11 located downstream of the aerobic tanks 7-9, and a disinfection tank 12 located downstream of the final sedimentation tank 11.

[0033] The water to be treated 2 flows from the primary sedimentation tank 10 through the supply path 14 and is supplied to the aerobic tanks 7-9. After aerobic treatment in the aerobic tanks 7-9, the water to be treated 2 is discharged as treated water 3 through the discharge path 15 and sent to the final sedimentation tank 11. The treated water 3 discharged from the final sedimentation tank 11 is sent to the disinfection tank 12 for disinfection, and then discharged from the disinfection tank 12 into rivers or the ocean, etc.

[0034] The water treatment facility 1 is equipped with a return route 16 for returning the sludge that has settled in the final sedimentation tank 11 to the aerobic tanks 7-9.

[0035] Aerobic tanks 7-9 each have a pair of left and right side walls 20 and a bottom wall 22. Multiple existing first aeration devices 23 are installed at the bottom of each of the aerobic tanks 7-9.

[0036] During normal operation, the water to be treated 2 is supplied from the primary sedimentation tank 10 to each aerobic tank 7-9, where it is aerated by the first aeration device 23 in each aerobic tank 7-9, and then sent as treated water 3 from each aerobic tank 7-9 to the final sedimentation tank 11.

[0037] When updating the water treatment facility 1, an immersion-type membrane separator 30 is used, as shown in Figure 3. The membrane separator 30 has multiple sets of membrane units 31 that separate solids and liquids from the water to be treated 2, an enclosure 32 that surrounds the sides of these membrane units 31, and a support frame 33.

[0038] The membrane unit 31 is provided on a support frame 33 and includes a plurality of membrane elements 36 housed in a case 35, a second aeration device 38 that generates a swirling flow 37 (see Figure 6) that swirls vertically along the membrane elements 36, and a water collection pipe 39 provided above the membrane elements 36.

[0039] The membrane element 36 consists of a filter plate with a filtration membrane attached. The water to be treated 2 that has passed through the filtration membrane is collected in the water collection pipe 39 as filtered water 40. The second aeration device 38 is located below the membrane element 36.

[0040] The enclosure 32 is provided on the support frame 33 and is formed by a peripheral wall 41 that is rectangular in shape in a plan view. Its lower end is submerged below the water surface 4 in the aerobic tanks 7-9, and its upper end protrudes above the water surface 4. The upper and lower ends of the enclosure 32 are open, and as a result, a communication opening 34 (an example of a communication part) is provided at the lower end of the enclosure 32 that communicates the inside and outside of the enclosure 32 below the water surface 4.

[0041] The support frame 33 can be suspended and fixed to the aerobic tanks 7-9, and includes an upper horizontal frame 43, a pair of left and right vertical frames 44 hanging down from the upper horizontal frame 43, and a lower horizontal frame 45 provided between the lower ends of both vertical frames 44.

[0042] Furthermore, the support frame body 33 has a submerged portion 47 that is submerged below the water surface 4 in the aerobic tanks 7-9 and an exposed portion 48 that is exposed above the water surface 4. The upper horizontal frame 43 is included in the exposed portion 48 and has supported portions 43a at both ends that are supported by the upper ends of the side walls 20 of the aerobic tanks 7-9.

[0043] The upper horizontal frame 43 supports a filtered water discharge pipe 50 that sends filtered water 40 to the downstream side of the disinfection tank 12, and an air supply pipe 51 that supplies air to the second aeration device 38. The filtered water discharge pipe 50 is connected to the water collection pipe 39 via a first connecting pipe 52. The air supply pipe 51 is connected to the second aeration device 38 via a second connecting pipe 53.

[0044] The enclosure 32 is attached to the upper horizontal frame 43. The lower horizontal frame 45 is provided with a floating body 55 that generates buoyancy for the support frame 33. The lower horizontal frame 45 and the floating body 55 are included in the submerged section 47.

[0045] A lower space 58 through which the treated water 2 flows is formed between the lower end of the enclosure 32 and the bottom wall 22 of the aerobic tanks 7-9. Additionally, a lateral space 59 through which the treated water 2 flows is formed between the outer surface of the enclosure 32 and the side wall 20 of the aerobic tanks 7-9.

[0046] The following describes a method for updating the water treatment facility 1 using a membrane separation device 30.

[0047] For example, aerobic tank 7 will be designated as a treatment tank to be replaced, while aerobic tanks 8 and 9 will be designated as treatment tanks not to be replaced.

[0048] The update method consists of the following four steps:

[0049] As shown in Figures 4 and 5, in the first step, a membrane separation device 30 having a membrane unit 31 is installed in one of the aerobic tanks 8 and 9 other than the one to be replaced (either aerobic tank 8 or aerobic tank 9). Then, bubbles 60 are released from the first aeration device 23 of the aerobic tanks 8 and 9 other than the one to be replaced to perform aeration, while the membrane unit 31 of the aerobic tank 8 separates the water to be treated 2 into solid and liquid. As a result, a portion of the water to be treated 2 supplied to the treatment tank 8 is separated into solid and liquid by the membrane unit 31 and discharged to the outside of the treatment tank 8, the remainder of the water to be treated 2 supplied to the treatment tank 8 is aerated by the first aeration device 23 and then discharged from the treatment tank 8 to the final sedimentation tank 11 as treated water 3, and the entire amount of water to be treated 2 supplied to the aerobic tank 9 is aerated by the first aeration device 23 and then discharged from the treatment tank 9 to the final sedimentation tank 11 as treated water 3.

[0050] In this process, as shown in Figures 3 and 5, the treated water 2 that has passed through the filtration membrane of the membrane element 36 is collected as filtered water 40 in the collection pipe 39, and sent from the collection pipe 39 through the first connecting pipe 52 and the filtered water discharge pipe 50 to the downstream side of the disinfection tank 12, where it is discharged into a river or the ocean.

[0051] Furthermore, by releasing bubbles 61 from the second aeration device 38 of the membrane separation device 30 to perform aeration, a swirling flow 37 is generated along the membrane element 36, as shown in Figure 6, and the filtration membrane of the membrane element 36 is cleaned by the swirling flow 37.

[0052] In the second step, the supply of water to be treated 2 from the primary sedimentation tank 10 to the treatment tank 7 to be replaced is stopped, and with the first aeration device 23 of the treatment tank 7 to be replaced stopped, the water to be treated 2 in the treatment tank 7 is discharged to the outside, emptying the treatment tank 7 and replacing the treatment tank 7. The replacement may include, for example, replacing the first aeration device 23 of the treatment tank 7 with a new one, or adding a first aeration device 23 to the treatment tank 7, or performing maintenance, inspection, and repair of machinery, electrical equipment, or the side walls 20 or bottom walls 22 of the treatment tank 7.

[0053] In the third step, the membrane separation device 30 that was installed in the aerobic tank 8 in the first step is removed.

[0054] In the fourth step, the water to be treated 2 is supplied from the primary sedimentation tank 10 to the newly refurbished aerobic tank 7. As before the refurbishment, the first aeration device 23 of the aerobic tank 7 is activated as shown in Figure 1 to aerate the water to be treated 2 in the aerobic tank 7, and the operation of the newly refurbished aerobic tank 7 is restarted.

[0055] In the renewal method, the second step is carried out while the first step is being performed, and after the second step is completed (i.e., after the treatment tank 7 has been renewed), the third and fourth steps are carried out simultaneously.

[0056] In the above embodiment, the second step is performed while the first step is being carried out, and after the second step is completed, the third and fourth steps are carried out simultaneously. However, the third and fourth steps may be performed in a different order of time. That is, the third step may be carried out first, followed by the fourth step, or the fourth step may be carried out first, followed by the third step.

[0057] In the above embodiment, aerobic tank 7 was designated as the treatment tank to be replaced, while aerobic tanks 8 and 9 were designated as treatment tanks not to be replaced. However, if aerobic tank 8 is designated as the treatment tank to be replaced and aerobic tanks 7 and 9 are not, or if aerobic tank 9 is designated as the treatment tank to be replaced and aerobic tanks 7 and 8 are not, the same procedure as described above can be followed for steps 1 to 4. This allows multiple aerobic tanks 7 to 9 to be replaced sequentially.

[0058] According to the renewal method described above, in the first step, as shown in Figures 4 and 5, a portion of the liquid to be treated 2 supplied to treatment tank 8 of the treatment tanks 8 and 9 other than the one to be renewed is separated into solid and liquid by the membrane unit 31 and discharged as filtered water 40 downstream of the disinfection tank 12 (an example outside of treatment tank 8), while the remaining liquid to be treated 2 supplied to treatment tank 8 is aerated by the first aeration device 23 and then discharged as treated water 3 to the final sedimentation tank 11 (an example outside of treatment tank 8). Therefore, the number of membrane units 31 can be reduced compared to the case where the entire amount of liquid to be treated 2 supplied to treatment tank 8 other than the one to be renewed is separated into solid and liquid by the membrane unit 31 and discharged as filtered water 40 downstream of the disinfection tank 12.

[0059] Furthermore, in the first step, the membrane unit 31 is surrounded by an enclosure 32 for solid-liquid separation. As a result, the liquid to be treated 2 inside the enclosure 32 is concentrated, and the sludge concentration of the liquid to be treated 2 inside the enclosure 32 becomes higher than that of the liquid to be treated 2 outside the enclosure 32. This allows the sludge concentration of the liquid to be treated 2 inside the enclosure 32 to be raised to a predetermined concentration suitable for membrane separation activated sludge treatment, and good treatment efficiency by the membrane units 31 can be maintained even with a reduced number of membrane units 31. In addition, the design flux of the membrane unit 31 can be increased.

[0060] For example, the MLSS outside the enclosure 32 is maintained at approximately 2000 mg / L, and the MLSS inside the enclosure 32 is maintained at approximately 10000 mg / L, but these values ​​are not exhaustive.

[0061] Furthermore, in the first step, while aeration is performed by the first aeration device 23 of the aerobic tanks 8 and 9 that are not to be replaced, the treated water 2 is separated into solid and liquid by the membrane unit 31 of the aerobic tank 8. This prevents a temporary decrease in the treatment capacity of the water treatment facility 1 when the treatment tank 7 that is to be replaced is emptied and replaced in the second step. In addition, the MLSS concentration of the treated water 3 flowing from the aerobic tanks 8 and 9 that are not to be replaced into the final sedimentation tank 11 is maintained at the same concentration as before, eliminating the need to change the water surface load in the final sedimentation tank 11, and allowing the solid-liquid separation treatment in the final sedimentation tank 11 to be carried out in parallel.

[0062] Furthermore, in the first step, when the membrane unit 31 is installed in the aerobic tank 8 as shown in Figures 4 and 5, the supported portion 43a of the support frame 33 of the membrane separation device 30 is supported by the side wall 20 of the aerobic tank 8, as shown in Figure 3. In this state, buoyancy is generated on the support frame 33 by the float 55, so the load (self-weight) of the membrane separation device 30 acting on the side wall 20 of the processing tank 8 via the supported portion 43a of the support frame 33 is reduced by the amount of buoyancy. As a result, reinforcement work on the side wall 20 of the processing tank 8 can be made unnecessary or significantly reduced.

[0063] (Second Embodiment) In the second embodiment, as shown in Figure 7, the membrane separation device 30 includes an airlift device 65 (an example of a discharge device) that discharges the liquid to be treated 2 inside the enclosure 32 to the outside, and an MLSS concentration meter 66 that measures the MLSS inside the enclosure 32.

[0064] The airlift device 65 includes a third aeration device 67 located in the lower inner part of the enclosure 32, and a discharge pipe 68 located inside the enclosure 32 and above the third aeration device 67. The discharge pipe 68 is an inverted L-shaped pipe with an inlet 69 at its lower end and an outlet 70 at its upper end. The inlet 69 opens to the inside of the enclosure 32 while submerged below the water surface 4, and the outlet 70 opens to the outside of the enclosure 32 at the same height as the water surface 4.

[0065] The following explains the operation of the above configuration.

[0066] The MLSS concentration inside the enclosure 32 is measured by the MLSS concentration meter 66. If the measured value is higher than the optimal concentration (e.g., 10,000 mg / L), the third aeration device 67 is activated, and bubbles 62 are released from the third aeration device 67. This creates an upward flow of the liquid to be treated 2 above the third aeration device 67, and the liquid to be treated 2 inside the enclosure 32 flows through the discharge pipe 68 from the inlet 69 (carried by the bubbles 62) and is discharged to the outside of the enclosure 32 from the outlet 70.

[0067] As a result, the liquid to be treated 2 outside the enclosure 32 flows into the inside of the enclosure 32 through the communication port 34 at the lower end of the enclosure 32, gradually decreasing the MLSS concentration inside the enclosure 32. When the measured value reaches the optimal concentration, the third aeration device 67 is stopped. This prevents the liquid to be treated 2 inside the enclosure 32 from being discharged to the outside of the enclosure 32 through the discharge pipe 68, and allows the MLSS concentration inside the enclosure 32 to be adjusted to a predetermined concentration suitable for membrane separation activated sludge treatment.

[0068] In the second embodiment described above, an air-lift device 65 is used as an example of a discharge device, but it is not limited to the air-lift device 65, and the liquid to be treated 2 inside the enclosure 32 may be discharged to the outside using a submersible pump or the like.

[0069] In the second embodiment described above, the optimal MLSS concentration (e.g., 10,000 mg / L) is used as the basis, but the optimal MLSS concentration range (e.g., 9,000 to 11,000 mg / L) may also be used as the basis.

[0070] In the second embodiment described above, an MLSS concentration meter 66 is provided inside the enclosure 32, but a DO meter (dissolved oxygen meter) may also be provided inside the enclosure 32. If the dissolved oxygen concentration (DO) of the treated water 2 inside the enclosure 32 becomes low, nitrification failure may occur, the membrane filtration performance of the membrane unit 31 may decrease, the membrane element 36 may become blocked between membranes, or the treated water quality may deteriorate.

[0071] Therefore, the dissolved oxygen concentration in the enclosure 32 is measured by a DO meter, and if the measured value is lower than the optimal concentration, the third aeration device 67 is activated to release bubbles 62 from the third aeration device 67. As a result, an upward flow of the liquid to be treated 2 is generated above the third aeration device 67, and the liquid to be treated 2 inside the enclosure 32 flows through the inlet 69 and the discharge pipe 68 together with the bubbles 62 and is discharged to the outside of the enclosure 32 from the outlet 70.

[0072] As a result, the liquid to be treated 2 outside the enclosure 32 flows into the inside of the enclosure 32 through the communication port 34 at the lower end of the enclosure 32, causing the dissolved oxygen concentration inside the enclosure 32 to gradually increase. When the measured value reaches the optimal dissolved oxygen concentration, the third aeration device 67 is stopped. This prevents the liquid to be treated 2 inside the enclosure 32 from being discharged to the outside of the enclosure 32 through the discharge pipe 68, and allows the dissolved oxygen concentration inside the enclosure 32 to be adjusted to a predetermined concentration suitable for membrane separation activated sludge treatment.

[0073] While the optimal dissolved oxygen concentration is used as the standard, the optimal dissolved oxygen concentration range may also be used as the standard.

[0074] Alternatively, both the MLSS concentration meter 66 and the DO meter may be placed inside the enclosure 32.

[0075] (Third embodiment) In the third embodiment, as shown in Figure 8, the enclosure 32 has a peripheral wall 41 and a bottom wall 75 provided at the lower end of the peripheral wall 41 and covering the area below the membrane unit 31. The bottom wall 75 is located above the first aeration device 23 of the aerobic tanks 7 to 9.

[0076] The bottom wall 75 is provided with a communication opening 34 (an example of a communication section) that connects the inside and outside of the enclosure 32 below the water surface 4. The bottom wall 75 slopes downward from the lower end of the peripheral wall 41 toward the communication opening 34. The communication opening 34 opens to the inside and outside of the enclosure 32 in the horizontal plane.

[0077] The following explains the operation of the above configuration.

[0078] In the first step, when aeration is performed by releasing bubbles 60 from the first aeration device 23 of the aerobic tanks 8 and 9 that are not to be replaced, bubbles 61 are released from the second aeration device 38 of the membrane separation device 30 of the aerobic tank 8 to perform aeration, which generates a swirling flow 37 along the membrane element 36, and the filtration membrane of the membrane element 36 is washed by the swirling flow 37.

[0079] At this time, since the lower part of the membrane unit 31 is covered by the bottom wall 75 of the enclosure 32, it is possible to suppress the large amount of bubbles 60 released from the first aeration device 23 from entering the inside of the enclosure 32 from below.

[0080] This prevents problems such as a large amount of bubbles 60 released from the first aeration device 23 entering the inside of the enclosure 32 and obstructing the smooth flow of the swirling flow 37, thereby maintaining good cleaning efficiency of the membrane element 36.

[0081] Although it is possible that some of the bubbles 60 released from the first aeration device 23 may enter the inside of the enclosure 32 through the communication port 34, the amount of bubbles 60 that enter the inside of the enclosure 32 in this way is very small and will not interfere with the smooth flow of the swirling flow 37.

[0082] Furthermore, since the bottom wall 75 slopes downward from the lower end of the peripheral wall 41 toward the communication opening 34, the bubbles 60 released from the first aeration device 23 are guided to the outside of the peripheral wall 41 as they rise along the slope of the bottom wall 75. As a result, the bubbles 60 released from the first aeration device 23 flow smoothly to the outside of the enclosure 32 without stagnating.

[0083] In the third embodiment described above, the communication opening 34 is provided in the bottom wall 75 of the enclosure 32, but it may also be provided in the lower part of the peripheral wall 41.

[0084] (Fourth embodiment) In the fourth embodiment, as shown in Figure 9, the communication opening 34 opens to the inside and outside of the enclosure 32 in a vertical plane.

[0085] According to this, the possibility that some of the bubbles 60 released from the first aeration device 23 may enter the inside of the enclosure 32 through the communication port 34 can be significantly reduced.

[0086] (Fifth embodiment) In the first embodiment described above, as shown in Figure 4, the peripheral wall 41 of the enclosure 32 is formed in a rectangular shape in a plan view. However, it is not limited to this shape, and for example, in the fifth embodiment, as shown in Figure 10, the peripheral wall 41 may be formed in a boat shape in a plan view.

[0087] In other words, the peripheral wall 41 is formed such that its width W gradually narrows from the upstream side to the downstream side of the liquid to be treated 2.

[0088] According to this, in water treatment facility 1 employing the OD method (oxidation ditch method), the flow velocity of the water to be treated 2 in aerobic tanks 7-9 is high. In contrast, by forming the peripheral wall 41 of the enclosure 32 in a boat shape as described above, the resistance to the flow of the water to be treated 2 is reduced, and the external force acting on the support frame 33 of the membrane separator 30 is reduced.

[0089] (Sixth Embodiment) In the first embodiment described above, as shown in Figure 3, the float 55 of the membrane separation device 30 is placed below the membrane unit 31 and is completely submerged below the water surface 4. However, in the sixth embodiment described below, as shown in Figure 11, the float 55 may be placed above the membrane unit 31 and float on the water surface 4.

[0090] The floating body 55 has a storage section 78 for storing air inside, and an opening 79 on its lower surface. Buoyancy is obtained by storing bubbles 61 released from the second aeration device 38 in the storage section 78 through the opening 79.

[0091] According to this, similar to the first embodiment described above, when the membrane unit 31 is installed in the aerobic tank 8, for example, in the first step, the supported portion 43a of the support frame body 33 of the membrane separation device 30 is supported by the side wall 20 of the aerobic tank 8. In this state, buoyancy is generated on the support frame body 33 by the float 55, so the load (self-weight) of the membrane separation device 30 acting on the side wall 20 of the processing tank 8 via the supported portion 43a of the support frame body 33 is reduced by the amount of buoyancy. As a result, reinforcement work on the side wall 20 of the processing tank 8 can be made unnecessary or significantly reduced.

[0092] In each of the above embodiments, as shown in Figure 1, three aerobic tanks 7 to 9 are provided in the water treatment facility 1, but two or more tanks may be provided.

[0093] In each of the embodiments described above, as shown in Figure 4, in the first step, the membrane separation device 30 is installed in either aerobic tank 8 or aerobic tank 9 of the aerobic tanks 8 and 9 that are not to be replaced. However, the membrane separation device 30 may also be installed in both aerobic tank 8 and aerobic tank 9.

[0094] The drawings schematically show the components, and the thickness, length, number, spacing, etc., of each component shown may differ from the actual dimensions due to the limitations of drawing creation. Furthermore, the shapes, numerical values, etc., of each component shown in the above embodiments are examples only and are not particularly limiting; various modifications are possible without substantially departing from the configuration of the present invention. [Explanation of symbols]

[0095] 1. Water treatment facility 2. Water to be treated (liquid to be treated) 4 Water surface (liquid surface) 7-9 Aerobic tank (treatment tank) 23 1st air diffuser 30 Membrane separation equipment 31 Membrane Units 32 Enclosure 33 Support frame 34 Communication port (communication part) 36 film elements 37 Swirling flow 38 Second air diffuser 41 Peripheral wall 43a Supported part 47 Submerged area 48 Exposed part 55 Floating body 65. Airlift device (discharge device) 75 Bottom wall

Claims

1. A method for updating a water treatment facility having multiple treatment tanks equipped with a first aeration device, A first step involves installing an immersion-type membrane unit in at least one treatment tank other than the one to be replaced, separating a portion of the liquid to be treated supplied to the treatment tank other than the one to be replaced into solid and liquid by the membrane unit and discharging it to the outside of the treatment tank, and then discharging the remaining liquid to be treated with a first aeration device and then discharging it to the outside of the treatment tank. With the first aeration device of the treatment tank to be replaced stopped, the second step is to replace the treatment tank to be replaced, The process includes a third step of removing the membrane units from processing tanks other than those to be replaced after the replacement. In the first step, solid-liquid separation is performed by surrounding the membrane unit with an enclosure whose lower end is submerged below the liquid surface in the processing tank and whose upper end protrudes above the liquid surface. A method for updating a water treatment facility, characterized by performing the second step while simultaneously performing the first step.

2. The method for updating a water treatment facility according to claim 1, characterized in that, in the first step, aeration is performed using a first aeration device of a treatment tank other than the one to be updated, while the liquid to be treated is separated into solid and liquid using a membrane unit.

3. The method for updating a water treatment facility according to Claim 1, characterized in that a communication portion is provided that connects the inside and outside of the enclosure below the liquid surface.

4. The method for updating a water treatment facility according to claim 3, characterized in that a discharge device is provided for discharging the liquid to be treated inside the enclosure to the outside.

5. The method for updating a water treatment facility according to claim 4, characterized in that the MLSS concentration of the liquid to be treated inside the enclosure is adjusted using a discharge device.

6. The membrane unit comprises a membrane element and a second diffuser that generates a swirling flow that swirls vertically along the membrane element, The enclosure has a peripheral wall that surrounds the lateral periphery of the membrane unit, and a bottom wall provided below the peripheral wall that covers the bottom of the membrane unit. The method for updating a water treatment facility according to claim 1, characterized in that the bottom wall is located above the first aeration device of the treatment tank.

7. A fourth step of activating the first aeration device of the updated treatment tank to restart the operation of the updated treatment tank, The method for updating a water treatment facility according to claim 1, characterized in that the second step is carried out while the first step is carried out, and then the third and fourth steps are carried out simultaneously or in alternating order.

8. A membrane separation device comprising a membrane unit and an enclosure body used in the water treatment facility renewal method described in Claim 1, The membrane unit and the enclosure are provided on the support frame. The support frame has a submerged portion that is submerged below the liquid surface in the processing tank and an exposed portion that is exposed above the liquid surface. The exposed portion of the support frame body has a supported portion that is supported by the processing tank. A membrane separation device characterized by having a floating body that generates buoyancy on a support frame.

9. A membrane separation apparatus comprising a membrane unit that separates a liquid to be treated from solid to liquid while immersed in the liquid to be treated in a treatment tank, and a support frame body that supports the membrane unit, The support frame has a submerged portion that is submerged below the liquid surface in the processing tank and an exposed portion that is exposed above the liquid surface. The exposed portion of the support frame body has a supported portion that is supported by the processing tank. The support frame is provided with a floating body that generates buoyancy and an enclosure that surrounds the sides of the membrane unit. A membrane separation apparatus characterized in that the enclosure body has its lower end submerged below the liquid surface in the processing tank and its upper end protruding above the liquid surface.

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