JP2015085206A - Separation membrane module cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cleaning method capable of facilitating separation of coagulated floc in which adsorbent is bound to coagulant from a membrane surface, and discharging the floc to the outside of a separation membrane module system.SOLUTION: A separation membrane module washing method after filtering raw water to which powder adsorbent and coagulant are added and mixed, includes: filtering the raw water to which only the powder adsorbent is added and mixed at a time of starting filtration; subsequently filtering the raw water to which the powder adsorbent and the coagulant are added and mixed; discharging water on a membrane primary side in a separation membrane module to an outside of a system after ending the filtration steps; discharging back-pressure washing drain water in the separation membrane module while performing back-pressure washing; executing either a step (a) of performing air washing while filling the membrane primary side in the separation membrane module with water, or a step (b) of performing air washing while feeding water to the membrane primary side in the separation membrane module; and subsequently discharging the water on the membrane primary side in the separation membrane module to the outside of the system.

Description

  The present invention relates to a method for cleaning a microfiltration membrane (MF membrane) module or an ultrafiltration membrane (UF membrane) module obtained by membrane filtration of raw water.

  Membrane separation methods have features such as energy saving, space saving, and improved filtered water quality, and therefore are widely used in various fields. For example, the application of microfiltration membranes and ultrafiltration membranes to water purification processes that produce industrial water and tap water from river water, groundwater and sewage treated water, and pretreatment in seawater desalination reverse osmosis membrane treatment processes Can be given.

  When raw water contains a large amount of soluble substances such as chromaticity components and odorous substances or oils, adsorbents such as powdered activated carbon and diatomaceous earth and flocculants such as aluminum sulfate and polyaluminum chloride are added to and mixed with raw water. Filtered water with good water quality can be obtained by performing membrane separation later (see, for example, Patent Documents 1 and 2).

  By continuing filtration, the amount of aggregated floc attached to the membrane surface increases, and the filtration flow rate decreases or the membrane filtration differential pressure rises. Therefore, air bubbles are introduced to the membrane primary side (raw water side), and the membrane Oscillating and touching the membranes together, the membrane filtration water is scraped away from the membrane surface, and the membrane filtration water in the opposite direction from the membrane filtration method from the membrane secondary side (filtrate side) to the membrane primary side Alternatively, physical cleaning such as back-pressure cleaning that pushes clear water under pressure to remove contaminants adhering to the membrane surface and membrane pores has been put into practical use (see, for example, Patent Documents 3, 4, and 5).

  Also, after draining the water on the primary side of the separation membrane module out of the system, the back pressure washing waste water in the separation membrane module is drained while performing back pressure washing, and then the membrane primary side in the separation membrane module There has been proposed a physical cleaning method in which water is filled with water to perform air cleaning (see, for example, Patent Document 6).

  This physical cleaning method once drains the water on the primary side of the membrane (preferably the water on the primary side of the membrane so that the water level on the primary side of the membrane in the separation membrane module is below the lower end of the separation membrane. The product is discharged out of the system), and back pressure cleaning is performed in a state where the periphery of the primary side of the membrane is gas. Therefore, in the back pressure cleaning, the adsorbent in the form of a powder is more easily peeled off from the surface of the membrane than in the liquid state where the water pressure is applied to the primary side of the membrane. Easily discharged. Then, by performing air cleaning for a shorter time than before, the remaining adsorbent that could not be peeled off from the film surface is almost completely discharged. Therefore, it is possible to greatly reduce the film abrasion derived from the adsorbent due to air cleaning. Moreover, when it continues to use for the filtration process, the cake filtration resistance derived from the adsorbent on the membrane surface is suppressed, and stable operation with a low membrane filtration differential pressure over a long period of time is possible.

  However, when the adsorbent and the flocculant are added and the raw water mixed is filtered, the flocs combined with the adsorbent and the flocculant are sticky even if the reverse pressure washing of the washing method is performed. Since it was difficult to peel off and it was difficult to be discharged out of the system of the separation membrane module in the subsequent air cleaning, the cake filtration resistance derived from the aggregated floc on the membrane surface increased, and stable operation was difficult.

JP 2002-336616 A JP 2007-319792 A JP 11-342320 A JP 2000-140585 A JP 2007-289940 A WO2011 / 122289

  In the method for cleaning a separation membrane module after adding raw powder adsorbent and flocculant and filtering the mixed raw water, the present invention easily separates the flocs flocs bonded with the adsorbent and the flocculant from the membrane surface. An object of the present invention is to provide a cleaning method that can be discharged out of the membrane module system.

In order to solve the above-described problems, the separation membrane module cleaning method of the present invention has the following characteristics.
(1) In the method for washing the separation membrane module after adding the powder-form adsorbent and flocculant and filtering the mixed raw water, only the powder-form adsorbent is added at the start of filtration, and the mixed raw water is filtered Concentrated layer formation process is performed, followed by adding powder-form adsorbent and flocculant, filtering the mixed raw water, and after completing the filtration process, the water on the primary side of the separation membrane module is discharged out of the system Next, the back pressure washing waste water in the separation membrane module is discharged while carrying out the back pressure washing, and then one of the following steps is performed, and then the water on the primary side of the membrane in the separation membrane module is used as a system. Cleaning method of separation membrane module discharged outside.
(A) The step of performing air cleaning by filling the membrane primary side in the separation membrane module with water (b) The step of performing air cleaning while supplying water to the membrane primary side in the separation membrane module (2) Concentrating the adsorbent In the layer formation step, the adsorbent addition concentration of raw water is A (g / m ³ ), only the adsorbent in powder form is added, and the membrane filtration flux of the raw water mixed is B (m ³ / (m ² · d)) In addition, when the adsorbent in the form of powder is added and the time for filtering the mixed raw water is C (min), the adsorbent adhesion amount per unit membrane area A × B × C / 1440 (g / m ² ) is 0. The membrane filtration method according to (1), which is not less than 1 (g / m ² ) and not more than 10 (g / m ² ).
(3) The method for cleaning a separation membrane module according to (1) or (2), wherein in the step (a), the membrane primary side is filled with back-pressure cleaning water and / or raw water to perform air cleaning.
(4) The method for cleaning a separation membrane module according to (1) or (2), wherein in the step (b), air cleaning is performed while supplying backwash water and / or raw water to the primary side of the membrane.
(5) After the filtration is completed, water on the primary side of the separation membrane module is discharged out of the system until the water level on the primary side of the separation membrane module is at least 1/3 or less of the length of the separation membrane. ) To the separation membrane module according to any one of (4).
(6) The method for cleaning the separation membrane module according to any one of (1) to (4), wherein after the filtration is completed, the water on the primary side of the membrane in the separation membrane module is entirely discharged out of the system.
(7) When the backwashing wastewater in the separation membrane module is discharged while performing backwashing, the water level on the primary side of the membrane in the separation membrane module is maintained at least 1/3 or less of the separation membrane length. The method for cleaning the separation membrane module according to any one of (1) to (6), wherein the backwash flow rate is controlled as described above.
(8) The method for cleaning a separation membrane module according to any one of (1) to (7), wherein an oxidizing agent is added to water used in the step (a) or (b).
(9) The cleaning method of the separation membrane module according to any one of (1) to (8), wherein the adsorbent in powder form includes at least one of powdered activated carbon, diatomaceous earth, bentonite, kaolin, montmorillonite, and zeolite.

  In the cleaning method of the separation membrane module of the present invention, only the powdered adsorbent is added at the start of filtration, and the mixed raw water is filtered to form an adsorbent concentrated layer formed of powdered adsorbent on the membrane surface. Subsequently, powder-form adsorbent and flocculant are added, and the mixed raw water is filtered to form a floc floc concentrate layer formed of powder-form adsorbent and flocculant outside the adsorbent concentrate layer. Perform the filtration step. After completing the filtration step, back pressure cleaning is performed in a state where the periphery of the primary side of the membrane is a gas.

  When powdered adsorbent and flocculant are added from the beginning of conventional filtration, and the mixed raw water is filtered and washed with back pressure, a cohesive flocs floc concentrated layer is formed directly on the membrane surface, so the membrane surface It was hard to peel off from. On the other hand, in the present invention, since there is an adsorbent concentrated layer that is easily separated and dispersed between the membrane surface and the aggregated floc concentrated layer, the aggregated floc concentrated layer is easily separated and easily discharged outside the separation membrane module system. Then, the remaining agglomerated floc concentrate layer that could not be completely peeled off from the membrane surface is almost completely discharged by performing air cleaning for a shorter time than before. Therefore, when it is continuously used for the filtration step, the cake filtration resistance derived from the aggregated floc concentrated layer is suppressed, and stable operation with a low membrane filtration differential pressure over a long period of time is possible.

It is an apparatus general | schematic flowchart which shows an example of the fresh water generator to which this invention is applied.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the drawings. In addition, this invention is not limited to the following embodiments.

  As shown in FIG. 1, for example, as shown in FIG. 1, the fresh water generator of the present invention includes an activated carbon slurry storage tank 1 that stores powdered activated carbon slurry, a slurry supply pump 2 that supplies powdered activated carbon to raw water, raw water, and powdered activated carbon. , A raw water storage tank 4 for storing raw water, a raw water supply pump 5 for supplying raw water, a flocculant storage tank 6 for storing flocculant, and a flocculant supply for supplying flocculant to raw water Pump 7, static mixer 8 for mixing and stirring raw water and coagulant, raw water valve 9 opened when raw water is supplied, MF / UF membrane module 10 for filtering raw water, and filtered water valve 11 opened for membrane filtration A filtrate storage tank 12 for storing the membrane filtrate obtained by the MF / UF membrane module 10, a backwash pump 13 for supplying the membrane filtrate to the MF / UF membrane module 10 and backwashing, and a backwash Do And an oxidant supply pump 15 for supplying an oxidant to water that fills the primary side of the membrane during air cleaning (that is, raw water or membrane filtered water used as back pressure cleaning water). And an oxidant storage tank 16 for storing the oxidant, an air vent valve 17 that is opened when performing reverse pressure cleaning or air cleaning, and a case where air is supplied below the MF / UF membrane module 10 for air cleaning. The air flush valve 18 that is opened to the air, the air blower 19 that is an air supply source for air washing of the MF / UF membrane module 10, and the membrane primary side of the MF / UF membrane module 10 are opened when water is discharged. A drain valve 20 is provided.

  In the above-mentioned membrane filtration fresh water generator, the adsorbent concentrated layer forming step is performed at the start of the filtration step. In the adsorbent concentrated layer forming step, the powdered activated carbon slurry stored in the activated carbon slurry storage tank 1 is supplied to the raw water storage tank 4 by the slurry supply pump 2. The raw water mixed and stirred with the powdered activated carbon by the stirrer 3 is supplied to the membrane primary side in the MF / UF membrane module 10 by operating the raw water supply pump 5 and opening the raw water valve 9. Furthermore, pressure filtration of the MF / UF membrane module 10 is started by opening the filtrate water valve 11. The filtrate is transferred from the membrane secondary side to the filtrate storage tank 12 through the filtrate valve 11. In the case of total filtration, the air vent valve 17, the backwash valve 14, the air wash valve 18, and the drain valve 20 are all closed.

  In the adsorbent concentration layer forming step, when only the powdered activated carbon is added from the start of filtration and the mixed raw water is filtered, an adsorbent concentration layer made of powdered activated carbon is gradually formed on the membrane surface. Subsequently, the flocculant supply pump 7 is operated to supply the flocculant stored in the flocculant storage tank 6 to the raw water mixed and stirred with the powdered activated carbon, and after mixing and stirring with the static mixer 8, the MF / UF membrane module 10. Filter with. By this filtration, an aggregated floc concentrated layer formed of powdered activated carbon and a flocculant is formed on the outer surface of the adsorbent concentrated layer formed of powdered activated carbon on the membrane surface, and a filtration step is performed.

In the adsorbent concentration layer forming step at the start of the filtration step, as a condition for forming an adsorbent concentration layer made of powdered activated carbon on the membrane surface, the adsorbent addition concentration of raw water is A (g / m ³ ), B (m ³ / (m ² · d)) is the membrane filtration flux of the raw water added and mixed with only the adsorbent, and C (min) is the time for filtering the raw water mixed with the powdered adsorbent only. In this case, the adsorbent adhesion amount A × B × C / 1440 (g / m ² ) per unit membrane area corresponding to the adsorbent concentrated layer is 0.1 (g / m ² ) or more and 10 (g / m ² ). Or less, more preferably 0.5 (g / m ² ) or more and 2 (g / m ² ) or less. If the adsorbent adhesion amount per unit membrane area falls within this range, the flocculant supply pump 7 may be operated to start forming a floc floc concentrated layer formed of powdered activated carbon and flocculant. By setting the adsorbent adhering amount per unit membrane area to 0.1 (g / m ² ) or more, it is possible to sufficiently obtain the action of peeling the aggregated floc concentrated layer when the membrane is washed. Moreover, the raise of the cake filtration resistance derived from the adsorbent concentration layer in a filtration process can be suppressed by making adsorbent adhesion amount per unit membrane area into 10 (g / m < ² >) or less.

  After the filtration step, the membrane is washed, for example, as follows.

  First, the raw water valve 9 and the filtrate water valve 11 are closed, the slurry supply pump 2, the raw water supply pump 5, and the flocculant supply pump 7 are stopped, and the filtration process of the MF / UF membrane module 10 is stopped. Thereafter, the MF / UF membrane module 10 is washed to discharge the adsorbent concentrated layer formed on the membrane surface and the aggregated floc concentrated layer formed outside the adsorbent concentrated layer to the outside of the system. At this time, first, the air vent valve 17 and the drain valve 20 are opened. When the water on the membrane primary side in the MF / UF membrane module 10 is discharged out of the membrane module system from the drain valve 20 below the MF / UF membrane module 10, the water level of the MF / UF membrane module 10 decreases, The periphery of the primary side of the film is in a gas state. Here, the membrane primary side is the side that supplies the raw water to be filtered, and the membrane secondary side is the side where the filtered water obtained by filtering the raw water through the membrane is present. . The water on the primary side of the membrane in the MF / UF membrane module 10 may remain, but at least half of the membrane is above the water surface so as to be in contact with the gas. Preferably, water is discharged until the water level becomes 1/3 or less of the vertical length of the separation membrane, more preferably the entire membrane is above the water surface and the entire membrane is in contact with gas.

  Thereafter, the backwash valve 14 is opened while the air vent valve 17 and the drain valve 20 are opened, and the backwash pump 13 is operated to perform back pressure washing using the membrane filtrate in the filtrate storage tank 12. I do. At this time, the back pressure washing waste water in the MF / UF membrane module 10 is discharged from the drain valve 20 below the MF / UF membrane module 10. Conventionally, powdered activated carbon and flocculant were added from the beginning of the filtration process, and the mixed raw water was filtered, so the coagulated floc concentrated layer, which is a combination of powdered activated carbon and flocculant, adheres directly to the membrane surface. Even when back pressure cleaning was performed in a state where no water pressure was applied to the primary side of the membrane, the aggregated floc was difficult to peel off from the membrane surface. In contrast, in the present invention, at the start of filtration, only powdered adsorbent is added, mixed raw water is filtered, then powdered activated carbon and flocculant are added, mixed raw water is filtered, and powdered activated carbon is applied to the membrane surface. The adsorbent concentration layer formed in step 1 and the flocs floc concentration layer formed with powdered activated carbon and flocculant are formed outside the adsorbent concentration layer and the filtration process is completed. Because there is an adsorbent concentration layer that is easy to peel and disperse in the middle, as the adsorbent concentration layer peels from the membrane surface, the floc floc concentrate layer also peels off, and the MF / UF membrane module is dropped or dropped on the membrane surface. 10 is discharged out of the system through the drain valve 20 from below.

  When back pressure cleaning is carried out while discharging the back pressure cleaning waste water in the MF / UF membrane module 10, it is more effective that the water pressure is not applied to the primary side of the membrane continuously during the back pressure cleaning on the adsorbent concentration layer and the outside thereof. Since the peeling effect of the coagulated floc concentrated layer located increases, the backwash flow rate is controlled so that the water level on the primary side of the membrane in the MF / UF membrane module 10 is maintained at least 1/3 or less of the separation membrane length. It is preferable. The higher the backwash flow rate, the higher the separation effect of the adsorbent concentration layer and the aggregated floc concentration layer located outside the adsorbent concentration layer, but the wastewater flow rate discharged from the lower part of the MF / UF membrane module 10 by its own weight is the MF / UF membrane. There is a limit depending on the size of the drain outlet of the module 10, and the water level on the primary side of the membrane rises and water pressure may be applied to the primary side of the membrane. Therefore, it is preferable to appropriately control the backwash flow rate according to the structure of the MF / UF membrane module 10.

  Thereafter, the drain valve 20 is closed, the membrane primary side in the MF / UF membrane module 10 is filled with water, the flush valve 18 is opened, and the air blower 19 is operated, so that the lower side of the MF / UF membrane module 10 Gas is supplied from and air cleaning is performed.

  As a method for filling the primary side of the membrane in the MF / UF membrane module 10 with water, the raw water valve 9 may be opened and the raw water supply pump 5 may be operated to supply the raw water, or the backwash valve 14 may be opened. Then, the backwash pump 13 may be operated to supply the membrane filtered water as backwash water. It is better to add the oxidant by operating the oxidant supply pump 15 to the raw water or the membrane filtrate supplied at this time (that is, the water that will fill the membrane primary side in the MF / UF membrane module 10 at the time of air washing). It is preferable because it has an effect of decomposing and removing organic substances accumulated on the membrane surface and membrane pores. In the conventional physical cleaning, the aggregated floc concentrated layer in the MF / UF membrane module 10 could not be sufficiently peeled off from the membrane surface, so that the oxidant added to the raw water or the membrane filtered water accumulates on the membrane surface or membrane pores. In contrast to the fact that the organic substances that have been used up are almost consumed by the powdered activated carbon before being decomposed and removed, in the present invention, it is possible to make maximum use of the oxidizing agent.

  Even if the air cleaning starts (a) the membrane primary side in the MF / UF membrane module 10 is previously filled with water, (b) water is supplied to the membrane primary side in the MF / UF membrane module 10. (That is, supplying raw water into the MF / UF membrane module 10 or performing back pressure cleaning during air cleaning). However, it is preferable to perform air cleaning while supplying water because the cleaning effect is enhanced.

  Thereafter, the air washing valve 18 is closed and the air blower 19 is stopped to finish the air washing. When raw water is supplied into the MF / UF membrane module 10 during air cleaning or when back pressure cleaning is continued, the raw water valve 9 and the backwash valve 14 are also closed, and the raw water supply pump 5 It is preferable that the washing pump 13 and the oxidant supply pump 15 are also stopped and the raw water supply and the back pressure washing are finished.

  Next, the drain valve 20 is opened, and the suspended substances that are separated from the membrane surface and the membrane pores and are suspended in the MF / UF membrane module 10 are discharged out of the system.

After drainage is completed, the drain valve 20 is closed, the raw water valve 9 is opened, the raw water supply pump 5 is operated to supply water, and the membrane primary side of the MF / UF membrane module 10 is filled with water. After that, if the air vent valve 17 is closed and the filtrate water valve 11 is opened, the MF / UF membrane module 10 returns to the filtration process, and the above process is repeated from the adsorbent concentrated layer formation process to continue the water production. The cleaning method of the present invention may be performed every time after the filtration step is completed, or may be performed occasionally in combination with another cleaning method. From the water on the primary side of the membrane discharged from the drain valve 20 below the MF / UF membrane module 10 before the back pressure cleaning, or from the drain valve 20 below the MF / UF membrane module 10 when the back pressure cleaning is performed. The discharged back pressure washing wastewater, the air washing wastewater discharged from the air vent valve 17 on the upper part of the MF / UF membrane module 10 or the drain valve 20 below the MF / UF membrane module 10 during or after the air washing is performed. It is preferable to separate the precipitate and reuse the supernatant water as raw water because the water recovery rate is increased. In addition to sedimentation separation, coagulation sedimentation separation, pressurized flotation separation, centrifugation, sand filtration separation, microfiltration / ultrafiltration membrane filtration separation, filter cloth filtration separation, fibrous filter filtration separation, cartridge filter Filtration separation, disk filter separation, filter press, belt press, vacuum dewatering, multiple disk dewatering, etc. can be selected, but the suspended solids contained in the wastewater are mainly coagulated flocs and are highly settled. Separation is suitable. Also, precipitation separation is preferable from the viewpoint of equipment cost, processing cost, and the like.

  Examples of the powder-shaped adsorbent in the present invention include powdered activated carbon, diatomaceous earth, bentonite, kaolin, montmorillonite, zeolite, cerium-based adsorbent, manganese dioxide, ion exchange resin, etc. Powdered activated carbon is preferably used when it contains a large amount of ingredients and odorous substances, and naturally derived clay minerals such as diatomaceous earth, bentonite, kaolin, and montmorillonite are preferably used when the raw water contains a large amount of oil. When the raw water contains a large amount of arsenic, boron, and fluorine, cerium-based adsorbent, manganese dioxide, and ion exchange resin are preferably employed.

  In the case of powdered activated carbon, the particle size of the powder-shaped adsorbent in the present invention is defined as a powder shape of less than 150 μm, as described in JIS K 1474: 2007. Similarly, other powder-shaped adsorbents are defined as those having a powder shape of less than 150 μm. Further, the smaller the particle size, the larger the specific surface area and the higher the adsorption ability, which is preferable. However, it is necessary to make it larger than the pore diameter of the separation membrane of the MF / UF membrane module 10 so as not to be mixed into the membrane filtrate.

  The raw material for the powdered activated carbon may be any of woody materials such as coconut shells and sawdust, and coal-based materials such as peat, lignite and bituminous coal.

  The flocculant in the present invention has an effect of reducing the concentration of high molecular organic substances during membrane filtration. Examples of organic flocculants include dimethylamine-based and polyacrylamide-based cationic polymer flocculants. On the other hand, polyaluminum chloride, polyaluminum sulfate, ferric chloride, ferric sulfate, ferric sulfate, polysilica iron, etc. can be used as the inorganic flocculant.

  The MF / UF membrane module 10 may be an external pressure type or an internal pressure type, but is preferably an external pressure type from the viewpoint of simplicity of pretreatment. The membrane filtration method may be a total filtration module or a cross flow filtration module, but a complete filtration module is preferred from the viewpoint of low energy consumption. Further, it may be a pressurization type module or an immersion type module, but the pressurization type module is preferable from the viewpoint that a high flux is possible.

  The separation membrane used in the MF / UF membrane module 10 is not particularly limited as long as it is porous, but an MF membrane (microfiltration membrane) or a UF membrane (limited (Outer filtration membrane) is used, or both are used in combination. For example, when removing turbid components, Escherichia coli, Cryptosporidium, etc., either the MF membrane or the UF membrane may be used. However, when removing viruses or high molecular organic substances, it is preferable to use the UF membrane. .

  Examples of the shape of the separation membrane include a hollow fiber membrane, a flat membrane, and a tubular membrane, and any of them may be used.

  The material of the separation membrane is polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetra Including at least one selected from the group consisting of a fluoroethylene-perfluoroalkyl vinyl ether copolymer, and a chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, polysulfone, cellulose acetate, polyvinyl alcohol, and polyethersulfone. Polyvinylidene fluoride (PVDF) is more preferable from the viewpoint of film strength and chemical resistance, and from the viewpoint of high hydrophilicity and strong stain resistance. Rironitoriru is more preferable. In addition, since the separation membrane made of the organic polymer resin described above has lower hardness than the adsorbent such as powdered activated carbon, bentonite and kaolin, it can be preferably used in the method for cleaning the separation membrane module of the present invention.

  The control method for the filtration operation may be constant flow filtration or constant pressure filtration, but constant flow filtration is preferred from the viewpoint that a constant amount of treated water can be obtained and the overall control is easy.

  According to the present invention described above, the cake filtration resistance derived from the aggregated floc concentrated layer can be suppressed, and stable operation with a low membrane filtration differential pressure over a long period of time is possible. However, it cannot be completely adsorbed by the coagulated floc-concentrated layer or powdered activated carbon, and it is difficult to completely remove organic substances derived from raw water adhering to the membrane surface, and iron, manganese, etc. oxidized by the oxidizing agent gradually precipitate on the membrane surface. Sometimes. Therefore, when the membrane filtration differential pressure reaches close to the pressure limit of the MF / UF membrane module 10, it is preferable to perform chemical cleaning at a high concentration.

  The chemical used for the cleaning can be selected after appropriately setting the concentration and holding time to such an extent that the film does not deteriorate. At least one of sodium hypochlorite, chlorine dioxide, hydrogen peroxide, ozone and the like can be selected. It is preferable to contain it because the cleaning effect on the organic matter is increased. In addition, it is preferable to contain at least one of hydrochloric acid, sulfuric acid, nitric acid, citric acid, oxalic acid and the like because the cleaning effect on aluminum, iron, manganese and the like is increased.

Example 1
In the apparatus shown in FIG. 1, one external pressure PVDF ultra-hollow fiber membrane module HFU-2020 (membrane area 72 m ² ) manufactured by Toray Industries, Inc. is used for the MF / UF membrane module 10, and the raw water valve 9 and The filtered water valve 11 is opened, the slurry supply pump 2 and the raw water supply pump 5 are operated, and the membrane water is filtered using river water in which the additive concentration of the powdered activated carbon is adjusted to 30 g / m ³ in the raw water storage tank 4. The constant flow filtration of the bundle 1.5 m ³ / (m ² · d) was started. Five minutes after the start of constant flow filtration, the flocculant supply pump 7 is operated, and the river water adjusted to 1 g-Al / m ^{3 of} polyaluminum chloride and 30 g / m ³ of powdered activated carbon is membrane filtered. The flow rate was filtered at a flow rate of 1.5 m ³ / (m ² · d) for 25 minutes, and the constant flow rate was filtered for a total of 30 minutes. The powder activated carbon adhesion amount per unit membrane area corresponding to the adsorbent concentrated layer at that time was 30 × 1.5 × 5/1440 = 0.156 g / m ² . 30 minutes after the start of constant flow filtration, the raw water valve 9 and the filtered water valve 11 are closed, the slurry supply pump 2, the raw water supply pump 5, and the coagulant supply pump 7 are stopped, and the filtration process of the MF / UF membrane module 10 is stopped. After that, the air vent valve 17 and the drain valve 20 were opened, and all the water on the membrane primary side in the MF / UF membrane module 10 was discharged. Then, with the air vent valve 17 and the drain valve 20 open, the backwash valve 14 is opened, the backwash pump 13 is operated, and the backwashing with a flow rate of 2 m ³ / (m ² · d) is performed for 1 min. . Thereafter, the backwash valve 14 and the drain valve 20 are closed, the backwash pump 13 is stopped, and at the same time the raw water valve 9 and the air washing valve 18 are opened, the raw water supply pump 5 and the air blower 19 are operated, and the MF / Air cleaning was performed for 1 minute while supplying air at an air flow rate of 100 L / min while supplying 75 L / min of raw water to the membrane primary side of the UF membrane module 10. Thereafter, the raw water valve 9 and the flush valve 18 are closed, the raw water supply pump 5 and the air blower 19 are stopped, and at the same time, the drain valve 20 is opened, and all the water on the membrane primary side in the MF / UF membrane module 10 is discharged. . Then, simultaneously with closing the drain valve 20, the raw water valve 9 is opened, the slurry supply pump 2 and the raw water supply pump 5 are operated, and the primary side of the membrane in the MF / UF membrane module 10 is supplied with raw activated carbon containing powdered activated carbon. Then, the filtered water valve 11 was opened, the air vent valve 17 was closed, the flow returned to the filtration step, and the above steps were repeated.

  As a result, the membrane filtration differential pressure of the MF / UF membrane module 10 was stable at 43 kPa after 4 months with respect to 18 kPa immediately after the start of operation.

(Example 2)
In the apparatus shown in FIG. 1, one external pressure PVDF ultra-hollow fiber membrane module HFU-2020 (membrane area 72 m ² ) manufactured by Toray Industries, Inc. is used for the MF / UF membrane module 10, and the raw water valve 9 and The filtered water valve 11 is opened, the slurry supply pump 2 and the raw water supply pump 5 are operated, and the membrane filtration flux using the factory waste water in which the additive concentration of bentonite is adjusted to 30 g / m ³ in the raw water storage tank 4. 1 m ³ / (m ² · d) constant flow filtration was started. After 5 minutes from the start of constant flow filtration, the flocculant supply pump 7 is operated, and the factory wastewater in which the addition concentration of polyaluminum chloride is adjusted to 2 g-Al / m ³ and the addition concentration of bentonite to 30 g / m ³ is filtered through a membrane. The bundle was filtered at a constant flow rate of 1 m ³ / (m ² · d) for 25 minutes, and a constant flow rate filtration was performed for a total of 30 minutes. The bentonite adhesion amount per unit membrane area corresponding to the adsorbent concentrated layer at that time was 30 × 1 × 5/1440 = 0.104 g / m ² . 30 minutes after the start of constant flow filtration, the raw water valve 9 and the filtered water valve 11 are closed, the slurry supply pump 2, the raw water supply pump 5, and the coagulant supply pump 7 are stopped, and the filtration process of the MF / UF membrane module 10 is stopped. After that, the air vent valve 17 and the drain valve 20 were opened, and all the water on the membrane primary side in the MF / UF membrane module 10 was discharged. Thereafter, with the air vent valve 17 and the drain valve 20 open, the backwash valve 14 is opened, the backwash pump 13 is operated, and the back pressure washing with a flux of 1.5 m ³ / (m ² · d) is performed for 1 min. Carried out. Thereafter, the backwash valve 14 and the drain valve 20 are closed, the backwash pump 13 is stopped, and at the same time the raw water valve 9 and the air washing valve 18 are opened, the raw water supply pump 5 and the air blower 19 are operated, and the MF Air cleaning was performed for 1 minute while supplying air at an air flow rate of 100 L / min while supplying 50 L / min of raw water to the membrane primary side of the / UF membrane module 10. Thereafter, the raw water valve 9 and the flush valve 18 are closed, the raw water supply pump 5 and the air blower 19 are stopped, and at the same time, the drain valve 20 is opened, and all the water on the membrane primary side in the MF / UF membrane module 10 is discharged. . Then, simultaneously with closing the drain valve 20, the raw water valve 9 is opened, the slurry supply pump 2 and the raw water supply pump 5 are operated, and the primary side of the membrane in the MF / UF membrane module 10 is supplied with raw activated carbon containing powdered activated carbon. Then, the filtered water valve 11 was opened, the air vent valve 17 was closed, the flow returned to the filtration step, and the above steps were repeated.

  As a result, the membrane filtration differential pressure of the MF / UF membrane module 10 was stable at 29 kPa even after 4 months, compared with 11 kPa immediately after the start of operation.

(Comparative Example 1)
In the apparatus shown in FIG. 1, one external pressure PVDF ultra-hollow fiber membrane module HFU-2020 (membrane area 72 m ² ) manufactured by Toray Industries, Inc. is used for the MF / UF membrane module 10, and the raw water valve 9 and The filtered water valve 11 is opened, the slurry supply pump 2, the raw water supply pump 5 and the flocculant supply pump 7 are operated, and the addition concentration of polyaluminum chloride is 1 g-Al / m ³ and the addition concentration of powdered activated carbon is 30 g / Example except that the river water adjusted to m ³ was filtered at a constant flow rate of 30 m with a membrane filtration flux of 1.5 m ³ / (m ² · d), and only an agglomerated floc concentrated layer was formed without forming an adsorbent concentrated layer. Same as 1.

  As a result, the membrane filtration differential pressure of the MF / UF membrane module 10 rapidly increased to 120 kPa after 83 days, compared to 18 kPa immediately after the start of operation.

(Comparative Example 2)
In the apparatus shown in FIG. 1, one external pressure PVDF ultra-hollow fiber membrane module HFU-2020 (membrane area 72 m ² ) manufactured by Toray Industries, Inc. is used for the MF / UF membrane module 10, and the raw water valve 9 and The filtered water valve 11 is opened, the slurry supply pump 2, the raw water supply pump 5 and the flocculant supply pump 7 are operated, and the addition concentration of polyaluminum chloride is 2 g-Al / m ³ and the addition concentration of bentonite is 30 g / m. Exactly the same as in Example 1 except that the factory wastewater adjusted to ³ was filtered at a constant flow rate with a membrane filtration flux of 1 m ³ / (m ² · d) for 30 min, and only the coagulated floc concentrated layer was formed without forming the adsorbent concentrated layer. Made the same.

  As a result, the membrane filtration differential pressure of the MF / UF membrane module 10 suddenly increased to 120 kPa after 98 days, compared with 11 kPa immediately after the start of operation.

DESCRIPTION OF SYMBOLS 1 Activated carbon slurry storage tank 2 Slurry supply pump 3 Stirrer 4 Raw water storage tank 5 Raw water supply pump 6 Coagulant storage tank 7 Coagulant supply pump 8 Static mixer 9 Raw water valve 10 MF / UF membrane module 11 Filtration water valve 12 Filtration water storage tank 13 Backwash pump 14 Backwash valve 15 Oxidant supply pump 16 Oxidant reservoir 17 Air vent valve 18 Air flush valve 19 Air blower 20 Drain valve

Claims (9)

In the method of cleaning the separation membrane module after adding powder-form adsorbent and flocculant and filtering the mixed raw water, only powder-form adsorbent is added at the start of filtration, and the adsorbent concentrated layer is formed to filter the mixed raw water After performing the process, adding powder-form adsorbent and flocculant, filtering the mixed raw water and finishing the filtration process, the water on the primary side of the membrane in the separation membrane module is discharged out of the system, , Discharge the backwash water in the separation membrane module while performing backwashing, then perform one of the following steps, and then discharge the water on the primary side of the separation membrane module out of the system. A method for cleaning the separation membrane module.
(A) Step of performing air cleaning by filling the membrane primary side in the separation membrane module with water (b) Step of performing air cleaning while supplying water to the membrane primary side in the separation membrane module In the adsorbent concentration layer forming step, the adsorbent addition concentration of raw water is A (g / m ³ ), only the adsorbent in the form of powder is added, and the mixed membrane filtration flux of raw water is B (m ³ / (m ^2). D)), adsorbent adhering amount per unit membrane area A × B × C / 1440 (g / m), where C (min) is the time for adding only powdery adsorbent and filtering the mixed raw water The membrane filtration method according to claim 1, wherein ² ) is 0.1 (g / m ² ) or more and 10 (g / m ² ) or less.   The method for cleaning a separation membrane module according to claim 1 or 2, wherein in the step (a), the membrane primary side is filled with back-pressure cleaning water and / or raw water to perform air cleaning.   The method for cleaning a separation membrane module according to claim 1 or 2, wherein in the step (b), air cleaning is performed while supplying backwash water and / or raw water to the primary side of the membrane.   The water on the primary side of the separation membrane module is discharged outside the system until the water level on the primary side of the membrane in the separation membrane module is at least 1/3 or less of the length of the separation membrane after completion of the filtration. The method for cleaning a separation membrane module according to any one of the above.   The method for cleaning a separation membrane module according to any one of claims 1 to 4, wherein after the filtration is completed, all of the water on the primary side of the membrane in the separation membrane module is discharged out of the system.   When draining the backwash water in the separation membrane module while performing backpressure washing, the water level on the primary side of the membrane in the separation membrane module is maintained at least 1/3 or less of the separation membrane length. The method for cleaning a separation membrane module according to claim 1, wherein the backwash flow rate is controlled.   The method for cleaning a separation membrane module according to any one of claims 1 to 7, wherein an oxidizing agent is added to water used in the step (a) or (b).   The method for cleaning a separation membrane module according to any one of claims 1 to 8, wherein the adsorbent in powder form includes at least one of powdered activated carbon, diatomaceous earth, bentonite, kaolin, montmorillonite, and zeolite.

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