JP4548081B2 - Cleaning method of hollow fiber membrane - Google Patents

Description

  The present invention relates to a method for cleaning a hollow fiber membrane, and more particularly to a method for cleaning a hollow fiber membrane used in a membrane filtration device of a water treatment facility, and a water treatment facility to which the method is applied.

  In the water treatment facility, first, raw water is taken from a river or the like, and this is coagulated and settled. In the coagulation sedimentation treatment, a flocculant such as polyaluminum chloride (PAC) is injected into the raw water to agglomerate suspended substances in the raw water to form flocs, and the flocs are precipitated. And drinking supernatant is obtained by ingesting the supernatant liquid after precipitation, filtering with sand etc., and also performing a sterilization process.

  In recent years, a method of performing membrane filtration in addition to the above aggregation and precipitation treatment has been developed. In the membrane filtration treatment, a hollow fiber membrane in which a UF membrane (ultrafiltration membrane) or an MF membrane (microfiltration membrane) is formed in a hollow thread shape is used, and raw water is passed through the hollow fiber membrane, thereby Remove turbid substances. Such a membrane filtration treatment can remove substances having a size larger than the pore size of the membrane, so that bacteria such as Escherichia coli can be removed depending on the choice of the pore size of the membrane.

By the way, in the membrane filtration treatment, since suspended substances adhere to the membrane surface, the filtration efficiency decreases with the treatment time, and the membrane surface needs to be cleaned. Therefore, it is known to perform a backwash process for passing water in the direction opposite to that during the filtration operation. Further, even when the backwashing process is performed, since the membrane surface is gradually blocked, it is known to periodically perform the chemical cleaning process for circulating the chemicals to the membrane module (see, for example, Patent Document 1). By performing such back washing treatment or chemical washing treatment, deposits attached to the membrane surface can be peeled off from the membrane surface, and the membrane filtration treatment can be performed stably over a long period of time.
JP 2004-130307 A

  However, when the membrane filtration treatment is performed after the coagulation sedimentation treatment as described above, there is a problem that sufficient washing effect cannot be obtained even if the back washing treatment or the chemical solution washing treatment is performed, and the progress of the clogging of the membrane surface is fast. was there. This is because when the fine metal floc remaining in the coagulation sedimentation treatment is subjected to membrane filtration treatment, the membrane surface adheres. Once this metal floc adheres to the membrane surface, back washing treatment or chemical washing treatment is performed. However, it was difficult to peel off. In addition, the conventional water treatment equipment has a problem that the amount of chemical used in the chemical cleaning process is large and the cost is remarkably high, and the film surface is damaged by the chemical cleaning process and the life of the film surface is shortened. was there.

  The present invention has been made in view of such circumstances, and even when a membrane filtration treatment is performed after a coagulation sedimentation treatment, a hollow fiber that can suppress membrane clogging and can reduce costs. It aims at providing the washing | cleaning method of a film | membrane, and the water treatment equipment to which it is applied.

In order to achieve the above object, the invention according to claim 1 is a hollow fiber membrane used in a membrane filtration device of a water treatment facility, and the treated water containing metal floc generated by the coagulation sedimentation treatment is subjected to membrane filtration. In the method for cleaning a hollow fiber membrane to be treated, the membrane module having the hollow fiber membrane is provided with a standing time for holding the sulfuric acid cleaning solution having a pH of 1 to 3 for 3 to 15 minutes , the acidic cleaning solution is drained from the membrane module to post-time, characterized in that it returned to the treated water prior to the flocculation process.

  According to the first aspect of the present invention, since the standing time for holding the acidic cleaning liquid in the membrane module for a predetermined time is provided, the cleaning effect of the hollow fiber membrane can be improved, and the use of the acidic cleaning liquid The amount can be greatly reduced. In particular, the metal flocs contained in the treated water after the coagulation sedimentation treatment can be dissolved without damaging the membrane surface by providing the standing time, and the membrane surface can be effectively prevented from being blocked. .

  Further, according to the invention of claim 1, since the acidic cleaning liquid discharged from the membrane module is returned to the treated water before the coagulation sedimentation treatment, the pH of the treated water can be lowered, which is suitable for the coagulation sedimentation treatment. PH can be adjusted. Therefore, the usage-amount of the pH adjuster used at the time of a coagulation sedimentation process can be reduced, and cost can be reduced.

According to the first aspect of the present invention, the membrane module having a hollow fiber membrane is provided with a standing time in which the sulfuric acid acidic cleaning solution having a pH of 1 to 3 is held for 3 to 15 minutes and left to stand. The metal floc attached to the hollow fiber membrane can be efficiently dissolved without damaging the surface.

According to a second aspect of the present invention, in the first aspect of the invention, the pH in the membrane module during the standing time is uniformly controlled. According to invention of Claim 3, the efficiency of melt | dissolution of a metal floc can be further improved by controlling pH in a membrane module uniformly.

According to a third aspect of the present invention, in the first or second aspect of the invention, the pH of the treated water before the coagulation sedimentation treatment is measured, and the pH of the acidic cleaning solution is adjusted according to the measured value of the pH. Features. Therefore, the pH of the treated water before the coagulation sedimentation treatment can be controlled to an appropriate value by the acidic cleaning liquid drained from the membrane module.

  According to the hollow fiber membrane cleaning method and the water treatment facility according to the present invention, since the acidic cleaning liquid is held in the membrane module for a predetermined time and allowed to stand, a cleaning effect of the hollow fiber membrane is provided. And the amount of the acid cleaning solution used can be greatly reduced.

  Hereinafter, preferred embodiments of a method for cleaning a hollow fiber membrane and a water treatment facility according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing a schematic configuration of a water treatment facility to which the present invention is applied. As shown in the figure, the water treatment facility 10 is mainly composed of a raw water tank 12, a coagulation sedimentation treatment apparatus 14, a supply tank 15, a membrane filtration treatment apparatus (membrane module) 16, a treatment water tank 18, and an acid cleaning liquid tank 20. .

  A raw water pipe 22 is connected to the raw water tank 12, and raw water is supplied and stored through the raw water pipe 22. The raw water tank 12 is provided with a pH meter 24, and the pH meter 24 measures the pH of the raw water in the raw water tank 12. The pH meter 24 is connected to a control device 62 described later, and a signal indicating the measured value of the pH meter 24 is output to the control device 62.

  The raw water tank 12 is connected to the coagulation sedimentation processing device 14 via a pipe 26, and the raw water in the raw water tank 12 is sent to the coagulation sedimentation processing device 14. The coagulation sedimentation processing apparatus 14 is an apparatus for coagulating suspended substances and dissolved organic substances in raw water to form flocs by adding a coagulant such as aluminum sulfate or polyaluminum chloride, and specifically, Consists of a coagulation basin, a sedimentation basin, a reservoir for treated water, and the like.

  A precipitate (aluminum hydroxide or the like) coagulated and precipitated by the coagulation sedimentation processing device 14 is withdrawn regularly or continuously via the sludge extraction tube 28 and transferred to the sludge treatment unit 30. The sludge treatment unit 30 includes a sludge concentration tank, a sludge dehydrator, and the like, and concentrates and dehydrates the precipitate. The concentrated and dehydrated precipitate is incinerated or disposed of as necessary.

  On the other hand, the supernatant liquid obtained by the coagulation sedimentation processing device 14 is supplied to the supply tank 15 through the piping 31 and temporarily stored, and when the membrane filtration processing device 16 performs the membrane filtration processing, the water is sent through the piping 32. Is done. The pipe 32 is provided with a pump X for feeding liquid and a valve A for opening and closing the pipe 32, and the valve A is operated by a control device 62 described later. Further, a drain pipe 34 is connected to the pipe 32 at a position between the valve A and the membrane filtration processing device 16. A valve D operated by the control device 62 is disposed in the middle of the drain pipe 34, and the tip of the drain pipe 34 is connected to the raw water tank 12. Therefore, the drain in the membrane filtration apparatus 16 can be returned to the raw water tank 12 via the drain pipe 34. Reference numeral 33 denotes an air supply pipe for supplying air to the membrane filtration processing device 16, and the air supply pipe 33 is connected to air supply means (not shown) such as a blower. The air supply pipe 33 is provided with a valve I, and the valve I is controlled to be opened and closed by a control device 62 described later.

  The membrane filtration device 16 includes a sealed cylindrical case 36, the pipe 32 is connected to the lower end of the case 36, and the treated water pipe 38 is connected to the upper end of the case 36. The inside of the case 36 is partitioned by a partition plate 40 into a lower part (hereinafter referred to as a primary side) and an upper part (hereinafter referred to as a secondary side) in the case 36. A plurality of openings 40a, 40a, ... are formed in the partition plate 40, and a cylindrical hollow fiber membrane 42 is attached so as to face each opening 40a. Therefore, the primary side and the secondary side in the case 36 are communicated only via the hollow fiber membrane 42, and suspended matter in the fluid is removed by the hollow fiber membrane 42 in the process in which the fluid flows from the primary side to the secondary side. . In FIG. 1, only three hollow fiber membranes 42 are shown as a schematic diagram showing the configuration of the membrane filtration apparatus 16, but in reality, thousands of hollow fiber membranes 42 are attached in parallel. The lower end of the hollow fiber membrane 42 is closed and fixed to the case 36 with a resin such as polyurethane. Furthermore, although only one case 36 is shown in FIG. 1, the present invention is not limited to this, and a plurality of cases 36 may be arranged in parallel.

  Examples of the material of the hollow fiber membrane 42 include a polysulfone resin hydrophilized with a polyvinyl alcohol resin, a polysulfone resin to which a crosslinked or non-crosslinked hydrophilic polymer is added, a polyvinyl alcohol resin, and a polyacrylonitrile resin. Resins, cellulose resins, hydrophilized polyolefin resins, polyvinylidene fluoride, and the like are used. The hollow fiber membrane 42 may be an ultrafiltration membrane or a microfiltration membrane, and the pore diameter is preferably 0.001 to 10 μm, more preferably 0.01 to 8 μm, and still more preferably 0.1 to 7 μm. The outer diameter of the hollow fiber membrane 42 is preferably set in the range of 200 to 3000 μm, and in the range of 500 to 2000 μm, from the viewpoint of securing the strength of the hollow fiber membrane 42 and the membrane area per module. It is more preferable. The thickness of the hollow fiber membrane 42 is preferably in the range of 50 to 700 μm, and more preferably in the range of 100 to 600 μm.

  A return pipe 46 is connected to the upper part of the primary side in the case 36 (that is, in the vicinity of the partition plate 40). The return pipe 46 is branched into four on the way, and the branch pipes 46a, 46b, 46c are connected to the raw water tank 12, the supply tank 15, and the pipe 32, respectively, and are connected to the branch pipes 46a, 46b, 46c. Are provided with valves E, F and G, respectively. On the other hand, the branch pipe 46d is arranged in the vicinity of the case 36 as an air vent pipe and is opened upward, and a valve H is provided. These valves E to H are controlled to open and close by a control device 62.

  The pH meters 44 and 44 are provided at the entrance / exit on the primary side of the case 36 (that is, the connection portion with the pipe 32 and the connection portion with the pipe 46). The pH meter 44 is connected to a control device 62 to be described later, and a signal indicating the measured value of the pH meter 44 is output to the control device 62. The number and arrangement of the pH meters 44 are not particularly limited, but are preferably distributed and arranged so that the pH distribution in the case 36 can be understood. For example, a plurality of pH meters 44 are directly attached to the case 36. It may be attached.

  The treated water pipe 38 connected to the upper end of the case 36 is connected to the treated water tank 18 via the valve B. Therefore, the treated water filtered by the membrane filtration treatment device 16 is sent and stored in the treated water tank 18 through the treated water pipe 38, and this treated water is drawn out as purified water.

  A cleaning liquid pipe 48 is connected to the treated water pipe 38 closer to the membrane filtration processing device 16 than the valve B, and the valve C is disposed in the cleaning liquid pipe 48. Further, the cleaning liquid pipe 48 is branched in the middle, one branch pipe 48 a is connected to the treated water tank 18 via the pump Y, and the other branch pipe 48 b is connected to the acid cleaning liquid tank 20 via the pump Z. Therefore, when the pump Y is driven, the treated water in the treated water tank 18 flows back to the membrane filtration device 16 via the treated water pipe 38. When the pump Z is driven, the acid cleaning liquid in the acid cleaning liquid tank 20 is sent to the membrane filtration device 16.

  A stirring means having a stirring blade 50 is provided inside the acid cleaning liquid tank 20 so that the inside of the acid cleaning liquid tank 20 can be stirred and mixed as necessary. The acid cleaning liquid tank 20 is provided with a pH meter 60, and this pH meter 60 is connected to the control device 62. Further, a sulfuric acid tank 52 storing sulfuric acid and a water tank 54 storing water are provided above the acid cleaning liquid tank 20. The sulfuric acid tank 52 and the water tank 54 are communicated with the acid cleaning liquid tank 20 through pipes 56 and 58, respectively, and valves J and K are provided in these pipes 56 and 58, respectively. Therefore, the acid cleaning liquid tank 20 can be replenished with the sulfuric acid in the sulfuric acid tank 52 or the water in the water tank 54 by opening and closing the valves J and K. Thereby, the pH of the acidic cleaning liquid in the acid cleaning liquid tank 20 can be adjusted. The valves J and K are opened and closed by the control device 62 and controlled so that the measured value of the pH meter 60 becomes a desired pH value. The desired pH value is a pH (usually 1 to 3) suitable for dissolving metal floc (aluminum) adhering to the membrane surface of the hollow fiber membrane 42, and this pH value is a pH meter of the raw water tank 12. 24 is adjusted.

  As described above, the valves A to K and the pumps X to Z are centrally managed by the control device 62. The control device 62 operates the valves A to K and the pumps X to Z on the basis of a timer for backwashing processing and a timer for acid cleaning processing (not shown) so as to switch between membrane filtration processing, backwashing processing, and acid cleaning processing. It has become. Each process will be described below with reference to FIG.

Controller 62, the time t ₁ and the acid cleaning treatment timer time t ₂ of the backwash process timer is reset to 0 first (step S1), the Thereafter, the membrane filtration process (step S2). In the membrane filtration process, the valves A and B in FIG. 1 are opened, the valves C to I are closed, and the pump X is driven. As a result, the supernatant liquid in the coagulation sedimentation processing device 14 is sent to the membrane filtration processing device 16, passed through the hollow fiber membrane 42 and filtered, and then sent to the treated water tank 18 and stored. By this membrane filtration operation, suspended substances and the like contained in the supernatant liquid are collected by the hollow fiber membrane 42 and removed. Further, the metal floc remaining after the coagulation sedimentation treatment is also attached to the hollow fiber membrane 42 and removed.

  In addition, said operation is a case of a total filtration system, and when selecting a cross flow system, the valve F is opened and a part of liquid is sent between the primary side of the membrane filtration apparatus 16 and the supply tank 15. Circulate. Thereby, a cross flow can be given to the membrane surface of the hollow fiber membrane 42, and blockage of the membrane surface can be suppressed.

When the membrane filtration operation is continuously performed, the membrane surface of the hollow fiber membrane 42 is blocked, so that the differential pressure between the primary side and the secondary side increases, and the membrane filtration efficiency decreases. Therefore, the control device 62 determines whether or not the timer time t ₁ has reached the period α until the backwash process is performed (step S3). It is determined whether t ₂ has reached the period β until the acid cleaning process is performed (step S4). If not, the back cleaning process is performed (step S5). If the predetermined period β has been reached, an acid cleaning process (step S6) is performed.

  In the backwash process, the valves C, E, and I are opened, the valves A, B, D, F, G, and H are closed, and the pump Y is driven. Thereby, the treated water in the treated water tank 18 is sent to the secondary side in the case 36 of the membrane filtration apparatus 16 and air is supplied to the primary side in the case 36. The treated water sent to the secondary side flows to the primary side, and at that time, the membrane surface of the hollow fiber membrane 42 flows backward in the direction opposite to that during the filtration operation. Therefore, the deposits attached to the film surface are peeled off, and the film surface is back-washed. Further, the air supplied to the primary side becomes bubbles and rises inside the case 36, whereby a shearing force is applied to the membrane surface of the hollow fiber membrane 42 and the membrane surface is washed. The cleaning waste liquid and the air after cleaning the membrane surface are returned to the raw water tank 12 via the return pipe 46 (branch pipe 46a). Therefore, the deposits peeled off from the film surface by backwashing can be removed by the coagulation sedimentation processing device 14. By periodically performing the backwashing operation as described above, the membrane blockage of the hollow fiber membrane 42 can be suppressed, the life of the hollow fiber membrane 42 can be extended, and the filtration operation can be stably performed over a long period of time. It can be carried out.

  By the way, as the back washing treatment is performed, the washing effect is reduced and the membrane is blocked. In particular, when membrane filtration is performed after the coagulation sedimentation treatment as in the present embodiment, the progress of membrane clogging is accelerated. This is because, among the deposits attached to the membrane surface of the hollow fiber membrane 42, the metal floc remains on the membrane surface even after the backwash treatment. Therefore, in the present embodiment, an acid cleaning treatment operation using an acidic cleaning liquid is performed every β during a certain period.

As shown in FIG. 3, in the acid cleaning process, an acidic cleaning solution is first injected (step S10). That is, the valves C and E in FIG. 1 are opened, the valves A, B, D, F, G, H, and I are closed, and the pump Z is driven. Thereby, the acidic cleaning liquid in the acid cleaning liquid tank 20 is supplied to the secondary side in the case 36 of the membrane filtration processing device 16. After the inside of the case 36 it is determined to have been filled with acidic cleaning solution, the time t ₂ of the backwash process timer is reset to 0 (step S11), and then proceeds to the stationary state (step S12). Whether or not the case 36 is filled with the acidic cleaning solution is determined based on whether or not the measured values of the pH meters 44 and 44 have reached a desired pH value (usually 1 to 3). The transition to the stationary state is performed by closing the valves A to I. That is, by closing the valves A to I, the acidic cleaning liquid is held in the case 36, and a stationary state in which the acidic cleaning liquid does not enter and leave the case 36 is obtained. The stationary state is maintained for a predetermined time γ. Here, the time γ in the stationary state is set to a time sufficient to dissolve the metal floc attached to the hollow fiber membrane 42, and is set to 3 to 15 minutes, for example. The stationary state time γ may always be a constant time, but may be set to gradually increase with the use time of the hollow fiber membrane 42.

  After holding the stationary state for a predetermined time γ (step S13), the acidic cleaning liquid is drained (step S14). The acidic cleaning liquid is drained by opening the valves D and E, whereby the acidic cleaning liquid in the case 36 is drained and sent to the raw water tank 12, and the raw water in the raw water tank 12 is mixed with the acidic cleaning liquid. As a result, the pH value of the raw water decreases. Therefore, the pH of the raw water, which is usually 7.5 to 7.8, can be lowered, and can be brought close to the range (6.8 to 7) suitable for the coagulation sedimentation treatment. Therefore, the usage-amount of the pH adjuster used at the time of a coagulation sedimentation process can be reduced.

After draining the acidic cleaning solution, it resets the timer time t ₂ to 0 (step S15), and rinsing processes of acid cleaning liquid is performed (step S16). The rinsing process is performed by opening the valves C, E, and I, closing the valves A, B, D, F, G, and H and driving the pump Y as in the backwash process. As a result, the treated water in the treated water tank 18 is supplied to the secondary side of the case 36 and air is supplied to the primary side of the case 36. Then, by flowing from the secondary side to the primary side in the case 36, the membrane surface of the hollow fiber membrane 42 is backwashed, and the shearing force is applied to the membrane surface by the air to be washed, and the acid remaining in the case 36 The cleaning solution is removed. That is, rinsing and backwashing in the case 36 are performed simultaneously. Such a rinsing process is performed for a time λ such that the acidic cleaning liquid in the case 36 is completely removed (step S17). The acid cleaning process is completed by the above process.

  In the above-described flow, the membrane filtration process, the backwash process, and the acid wash process are switched by a timer, but the present invention is not limited to this, and the differential pressure between the primary side and the secondary side of the hollow fiber membrane 42 And the processing may be switched when the measured value exceeds a predetermined threshold value.

  FIG. 4 shows the relationship between the dissolution time of the metal floc adhered to the membrane surface of the hollow fiber membrane 42 and the standing time. As shown in the figure, even though the acidic cleaning solution having a pH of 4 was held in the case 36, the metal floc adhered to the film surface could not be dissolved, whereas the acidic cleaning solution having a pH of 1 to 3 was kept in the case 36 for a predetermined time. The metal floc on the film surface can be dissolved by holding and standing. As shown in FIG. 4, the standing time for holding the acidic cleaning solution was 3 minutes or more (preferably 5 minutes or more), and a sufficient effect was obtained. In addition, the cleaning effect did not increase even after holding for more than 15 minutes. Therefore, it can be seen that, even if maintained for more than 15 minutes, the membrane surface of the hollow fiber membrane 42 becomes more painful due to the acidic cleaning liquid, and instead the life of the hollow fiber membrane 42 is shortened. As described above, the standing time for holding the acidic cleaning liquid is preferably 3 minutes or more and 15 minutes or less, and more preferably 5 minutes or more and 15 minutes or less.

  FIG. 5 shows the change over time in the differential pressure before and after the hollow fiber membrane 42. In the figure, the dotted line is a comparative example in which the acid cleaning process was not performed, and the solid line is the present example in which the acid cleaning process was performed. In the figure, only large fluctuations in measured values are shown by solid lines or dotted lines. Actually, the differential pressure fluctuates slightly before and after backwashing or acid washing.

  As shown in the figure, in the comparative example in which the acid cleaning treatment was not performed, the differential pressure increased at an accelerated rate in about one month, and after two months, the differential pressure increased so that it was not usable. In contrast, in this example in which the acid cleaning treatment was periodically performed, the differential pressure did not increase, and sufficient filtration performance was obtained in a certain period. Therefore, in the present embodiment, the performance of the hollow fiber membrane 42 can be reliably recovered by performing the acid cleaning treatment periodically, and the treatment can be performed stably over a long period of time.

  Although not shown in FIG. 5, the measurement was also performed when the acidic cleaning liquid was supplied to the hollow fiber membrane 42 while circulating. In this case, the fluctuation of the differential pressure was similar to that of this example, but the pain of the hollow fiber membrane 42 was more severe than that of this example, and the life of the hollow fiber membrane 42 was shorter. Further, when the acidic cleaning liquid is circulated, there is a problem that the amount of the acidic cleaning liquid used is much larger than the case where the standing time is provided as in this embodiment, and the power cost of the circulating pump is increased. There was also.

  As described above, in the present embodiment, the acidic cleaning liquid is kept in the case 36 for a predetermined time and is allowed to stand, so that the membrane surface of the hollow fiber membrane 42 is not damaged. Metal flocs adhering to the surface can be dissolved, the life of the hollow fiber membrane 42 can be extended, the amount of acidic cleaning liquid used and the power of the circulation pump can be reduced, and membrane cleaning can be performed at low cost. be able to.

  By the way, in the acid cleaning treatment described above, the pH of the acidic cleaning liquid sent to the case 36 is adjusted by the pH of the raw water in the raw water tank 12 (that is, the measured value of the pH meter 24). Specifically, the pH of the raw water is compared with 6.8 to 7 suitable for the coagulation sedimentation treatment. If the pH of the raw water is much higher than this, the pH of the acid cleaning liquid tank 20 is decreased to 1 Adjust to a value close to. Moreover, when the pH of raw | natural water is close to the said suitable range, the pH of the acid cleaning liquid tank 20 is raised and it adjusts so that it may become a value close | similar to 3. As a result, when the waste solution of the acidic cleaning liquid is mixed with the raw water in the raw water tank 12, the pH of the raw water can be made closer to 6.8 to 7, and the amount of the pH adjuster used during the coagulation sedimentation process can be greatly reduced. can do.

  In the above-described embodiment, the pH may be made uniform in the case 36 when the acidic cleaning liquid is allowed to stand. For example, when a predetermined difference occurs between the measured values of the two pH meters 44, 44, the valve I is opened and air is supplied into the case 36 for several seconds. When the air rises in the case 36 as bubbles, a shearing force is applied to the membrane surface of the hollow fiber membrane 42 to clean the membrane surface, and the inside of the case 36 is agitated, so that the pH in the case 36 is uniform. It becomes. Thereby, the metal floc adhering to the membrane surface of the hollow fiber membrane 42 is effectively dissolved, and the cleaning effect of the hollow fiber membrane 42 is increased. The air in the case 36 is pulled out from the branch pipe 46d by opening the valve H.

  The method for homogenizing the pH in the case 36 is not limited to the supply of air, and an acidic cleaning solution may be circulated. In the circulation of the acidic cleaning liquid, the valves C and E are closed and the pump Z is stopped, and then the valves A and G are opened to drive the pump X. Thereby, the acidic cleaning liquid in the case 36 is circulated through the branch pipe 46c and the pipe 32, and the pH in the case 36 is made uniform.

  In addition, you may make it perform the supply of the air mentioned above, and the circulation of acidic cleaning liquid regularly with less frequency than an acid cleaning process.

The schematic diagram which shows the structure of the water treatment equipment which concerns on this invention Flow chart showing control method The flowchart explaining the acid cleaning process of FIG. Diagram showing the effect of acid cleaning treatment The figure which shows the time-dependent change of the differential pressure | voltage in a membrane filtration processing apparatus

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Water treatment equipment, 12 ... Raw water tank, 14 ... Coagulation sedimentation processing apparatus, 15 ... Supply tank, 16 ... Membrane filtration processing apparatus, 18 ... Treatment water tank, 20 ... Acid washing liquid tank, 22 ... Raw water pipe, 24 ... pH meter 36 ... Case, 40 ... Partition plate, 42 ... Hollow fiber membrane, 44 ... pH meter, 52 ... Sulfuric acid tank, 54 ... Water tank, 62 ... Control device, AK ... Valve, XZ ... Pump

Claims (3)

In a hollow fiber membrane used in a membrane filtration device of a water treatment facility, the membrane filtration treatment of the treated water containing metal floc generated by the coagulation sedimentation treatment,
In the membrane module having the hollow fiber membrane, a sulfuric acid acidic cleaning solution having a pH of 1 to 3 is held for 3 to 15 minutes and allowed to stand,
A method for washing a hollow fiber membrane, wherein the acidic washing liquid drained from the membrane module after the standing time is returned to the treated water before the coagulation sedimentation treatment.   The method for cleaning a hollow fiber membrane according to claim 1, wherein the pH of the cleaning liquid in the membrane module during the standing time is uniformly controlled.   The pH of the treated water before the coagulation sedimentation treatment is measured, and the pH of the sulfuric acid acidic washing solution is adjusted according to the measured value of the pH, The hollow fiber membrane washing according to claim 1 or 2 Method.

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