JP2015077530A - Water production method and water production device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cleaning method of a membrane module and a water production method where equipment cost, the installation space of equipment and electricity charge can be reduced and contaminants adhered to the whole surface of a separation membrane can be significantly peeled and removed.SOLUTION: In a water production method where raw water is supplied to the lower side of the separation membrane primary side of a membrane module 4 which is disposed so that the direction of a separation membrane is vertical and membrane-filtered water is obtained from a separation membrane secondary side by filtering the raw water with the separation membrane, a cleaning step where aspirator supply water is supplied to an aspirator 12 and a gas-liquid mixed fluid discharged from the aspirator 12 is supplied to the lower side of the separation membrane primary side of the membrane module 4 is temporarily performed.

Description

  The present invention relates to a fresh water generating method and a fresh water generating apparatus for supplying raw water to a membrane module having a separation membrane to obtain membrane filtered water, and more particularly to a method for cleaning a membrane module.

  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, microfiltration membranes and ultrafiltration membranes are applied to water purification processes that produce industrial water and tap water from river water, groundwater and sewage treated water, and to pretreatment in seawater desalination reverse osmosis membrane treatment processes. Is mentioned. Nanofiltration membranes and reverse osmosis membranes can be applied to advanced water purification processes that remove mold odor, chromaticity, hardness components, etc. that cannot be removed with microfiltration membranes or ultrafiltration membranes, seawater desalination, brine water desalination, Application to pure water production and the like can be mentioned.

  If membrane filtration of raw water is continued, the amount of membrane contaminants such as suspended matter, humic substances, and microorganism-derived proteins increases on the surface of the separation membrane and in the pores of the separation membrane as the amount of membrane filtration water increases. A decrease in filtration flow rate or an increase in membrane filtration differential pressure becomes a problem.

  Therefore, air is supplied to the primary side (raw water side) of the separation membrane, the separation membrane is swung, and the separation membranes are brought into contact with each other to remove contaminants adhering to the separation membrane surface. Contaminants adhered to the surface of the separation membrane or in the pores of the separation membrane by pushing the membrane filtration water or clarified water with pressure from the secondary side (membrane filtration water side) to the separation membrane primary side in the opposite direction to the membrane filtration method Physical cleaning such as back-pressure cleaning that removes contaminants attached to the separation membrane surface by increasing the flow velocity of the membrane surface and increasing the flow velocity on the membrane surface and shearing force generated by the water flow Has been put into practical use (Patent Document 1).

  As the air cleaning, a method of supplying bubbles while moving the water level in the membrane module upward and / or downward has been proposed (Patent Documents 1-4). The water surface is a pulsating surface of extremely large and strong waves due to the collapse of bubbles. Therefore, when the pulsating surface moves from above to below or from below to above, the contaminants adhering to the separation membrane surface are effectively peeled off. Further, since the pollutants in the peeled membrane module are discharged out of the membrane module system in a short time, the separation membrane is hardly rubbed, and there is an advantage that the life of the membrane module is extended.

  In addition, as the flushing cleaning, there has been proposed a method of supplying raw water to an aspirator and supplying a gas-liquid mixed fluid discharged from the aspirator into the membrane module (Patent Documents 5 and 6). There is an advantage in that contaminants on the surface of the separation membrane are peeled and removed by a water flow and a shearing force of bubbles without using a blower or a compressor.

JP 11-342320 A Japanese Patent Laid-Open No. 4-126528 JP 7-47245 A JP 2006-281163 A Japanese Patent Publication No. 52-38947 JP 54-56082 A

  However, in the method of supplying bubbles while moving the water level in the membrane module upward, it is necessary to operate both the raw water supply pump that supplies raw water into the membrane module and the blower or compressor that supplies air into the membrane module. However, there was a problem that the equipment cost and the installation space for the equipment were large, and the electricity bill was high.

  On the other hand, in the methods described in Patent Documents 5 and 6 in which raw water is supplied to an aspirator and the gas-liquid mixed fluid discharged from the aspirator is supplied into the membrane module, the membrane module is placed horizontally, that is, the flow of the gas-liquid mixed fluid Is installed in parallel to the ground, so that it is easy to install the module, but when external pressure type membrane modules other than internal pressure hollow fiber membranes, internal pressure tubular membranes and monolith membranes are long Since the bubbles of the gas-liquid mixed fluid move upward from the membrane module as they move away from the inlet of the gas-liquid mixed fluid, the bubbles become non-uniform. In particular, when reaching a distance of 1 m or more from the inflow port, the separation membrane surface below the membrane module does not come into contact with bubbles, and there is a problem that the effect of peeling and removing contaminants on the separation membrane surface is remarkably reduced.

  Therefore, according to the present invention, in the method for cleaning the membrane module, it is possible to reduce the equipment cost, the installation space of the equipment, and the electricity bill, and it is possible to remarkably peel and remove the contaminants attached to the entire membrane surface. Another object of the present invention is to provide a fresh water generation method and a fresh water generation apparatus including a simple washing step.

  In order to solve the above problems, a fresh water generation method and a fresh water generator of the present invention have the following characteristics.

  (1) The raw water is supplied to the lower part of the separation membrane primary side of the membrane module installed so that the separation membrane is in the vertical direction, and the raw water is filtered by the separation membrane, and the membrane filtration is performed from the separation membrane secondary side. A water production method for obtaining water, comprising temporarily supplying aspirator supply water to an aspirator and supplying a gas-liquid mixed fluid discharged from the aspirator to a lower part of the separation membrane primary side of the membrane module A method for producing fresh water, characterized in that it is performed.

  (2) The fresh water generation method according to (1), wherein at least a part of the aspirator supply water is raw water or membrane filtered water.

  (3) Before supplying the gas-liquid mixed fluid to the lower part of the separation membrane primary side of the membrane module, the water on the separation membrane primary side of the membrane module is discharged out of the system. (1) or (2) The fresh water generation method of description.

  (4) Supplying the gas-liquid mixed fluid to the lower part of the separation membrane primary side of the membrane module, collecting at least part of the water discharged from the separation membrane primary side of the membrane module, and mixing it with the raw water The fresh water generation method according to any one of (1) to (3).

  (5) The fresh water generation method according to (4), wherein the water discharged from the primary side of the separation membrane of the collected membrane module is separated into suspended matter and clarified water, and the clarified water is mixed with the raw water. .

  (6) The fresh water generation method according to any one of (1) to (5), wherein the separation membrane is a microfiltration membrane or an ultrafiltration membrane.

  (7) Before supplying the gas-liquid mixed fluid to the lower part of the separation membrane primary side of the membrane module and / or simultaneously, supplying the membrane filtrate from the separation membrane secondary side of the membrane module to the membrane module. The fresh water generation method according to (6), wherein reverse pressure washing is performed by pumping to the separation membrane primary side.

  (8) The fresh water generation method according to (7), wherein an oxidizing agent is added to the membrane filtrate when performing back-pressure washing.

  (9) The membrane filtrate is supplied to a nanofiltration membrane module or a reverse osmosis membrane module and separated into permeated water and concentrated water, and at least a part of the concentrated water is used as an aspirator supply water, (6) The fresh water generation method in any one of (8).

  (10) The fresh water generation method according to any one of (1) to (5), wherein the separation membrane is a nanofiltration membrane or a reverse osmosis membrane.

  (11) Before supplying the raw water to the lower part of the membrane module on the primary side of the separation membrane, a membrane is formed by a microfiltration membrane module or an ultrafiltration membrane module which is a second membrane module installed in the previous stage of the membrane module The fresh water generation method according to (10), wherein filtration is performed.

  (12) supplying the gas-liquid mixed fluid to a lower part of the separation membrane primary side of the membrane module, recovering at least a part of the water discharged from the separation membrane primary side of the membrane module, The fresh water generation method according to (11), which is supplied to the membrane module.

  (13) A membrane module that filters raw water through a separation membrane installed in a vertical direction and discharges the membrane filtrate from the secondary side of the separation membrane, and supplies raw water to a lower portion of the separation membrane primary side of the membrane module A raw water supply unit, an aspirator for mixing a part of aspirator supply water and gas and supplying a gas-liquid mixed fluid to the lower part of the separation membrane primary side of the membrane module, and an aspirator for supplying the aspirator supply water to the aspirator A fresh water generator comprising a supply water supply unit.

  (14) The raw water supply pipe through which the raw water is supplied to the lower part of the membrane module on the primary side of the separation membrane is branched, and the aspirator supply water supply unit supplies the raw water to the aspirator as the aspirator supply water. (13) The fresh water generator described in (13).

  (15) The membrane filtrate discharge pipe from which the membrane filtrate is discharged from the separation membrane secondary side of the membrane module is branched, and the aspirator supply water supply unit uses the membrane filtrate as the aspirator supply water. The fresh water generator according to (13), wherein the fresh water generator is supplied to the aspirator.

  In the method for cleaning a membrane module of the present invention, since an aspirator and an existing raw water pump are used without using air supply equipment such as a blower and a compressor, equipment costs, equipment installation space, and electricity costs can be reduced. In addition, by installing the membrane module in a vertical method, bubbles come into contact with the entire separation membrane surface, and contaminants attached to the entire separation membrane surface can be markedly removed.

It is an apparatus schematic flowchart which shows an example of the desalination apparatus (pressure type membrane module) to which the 1st Embodiment of this invention is applied. It is an apparatus general | schematic flowchart which shows another example of the fresh water generator (pressurization type membrane module) to which the 1st Embodiment of this invention is applied. It is an apparatus schematic flowchart which shows another example of the fresh water generator (pressurization type membrane module) to which the 1st Embodiment of this invention is applied. It is an apparatus schematic flowchart which shows an example of the desalination apparatus (immersion type membrane module) to which the 1st Embodiment of this invention is applied. It is an apparatus schematic flowchart which shows another example of the fresh water generator (immersion type membrane module) to which the 1st Embodiment of this invention is applied. It is an apparatus general | schematic flowchart which shows an example of the desalinator to which the 2nd Embodiment of this invention is applied. It is an apparatus general | schematic flowchart which shows another example of the fresh water generator to which the 2nd Embodiment of this invention is applied. It is an apparatus schematic flowchart which shows an example of the conventional fresh water generator. It is an apparatus schematic flowchart which shows another example of the conventional fresh water generator.

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

  For example, as shown in FIG. 1, a fresh water generator targeted by the present invention includes a raw water storage tank 1 that stores raw water, a raw water supply pump 2 that supplies raw water, and a raw water valve 3 that is opened when the raw water is supplied. The membrane filtration water obtained by the microfiltration membrane / ultrafiltration membrane module 4 for membrane filtration of the raw water, the filtration water valve 5 opened during membrane filtration, and the microfiltration membrane / ultrafiltration membrane module 4 are stored. Microfiltration membrane / ultrafiltration membrane filtrate storage tank 6, backwash pump 7 that operates when supplying membrane filtration water to microfiltration membrane / ultrafiltration membrane module 4 and backwashing, and backwashing A backwash valve 8 that is sometimes opened, an oxidant supply pump 9 that operates when an oxidant is added to the backwash water, an oxidant storage tank 10 that stores the oxidant, and a microfiltration membrane / ultrafiltration membrane Open when supplying gas-liquid mixed fluid to the lower part of the separation membrane primary side of the module 4 A flush valve 11, an aspirator 12 that supplies raw water and air to discharge a gas-liquid mixed fluid, a check valve 13 that prevents backflow to the aspirator 12, and a separation membrane of the microfiltration membrane / ultrafiltration membrane module 4 Drain valve 14 that opens when the primary side water is discharged from the bottom, and air vent that opens when the primary side air and water of the separation membrane of the microfiltration membrane / ultrafiltration membrane module 4 are discharged from above A recovery tank 16 for recovering water discharged through the air vent valve 15 from above the valve 15 and the microfiltration membrane / ultrafiltration membrane module 4; A settling tank 17 is provided for separation.

In the above-described fresh water generator, in a normal filtration process, the raw water stored in the raw water storage tank 1 is converted into a microfiltration membrane / ultrafiltration membrane by operating the raw water supply pump 2 with the raw water valve 3 open. The microfiltration membrane / ultrafiltration membrane module 4 is pressure-filtered by supplying it to the lower part of the separation membrane primary side of the module 4 and opening the filtrate water valve 5. The membrane filtrate is transferred from the secondary side of the separation membrane to the microfiltration membrane / ultrafiltration membrane filtrate storage tank 6 through the filtration water valve 5. In the case of the total amount filtration, the backwash valve 8, the air wash valve 11, the drain valve 14, and the air vent valve 15 are all closed. The filtration time is preferably set as appropriate according to the raw water quality, membrane permeation flux, etc., but in the case of constant flow filtration, the predetermined membrane filtration differential pressure or membrane filtration water volume [m ³ ], in the case of constant pressure filtration, The filtration time may be continued until a predetermined membrane filtration flow rate [m ³ / day] or membrane filtration water amount [m ³ ] is reached. The membrane filtration flow rate is the amount of membrane filtration water per unit time.

  In the fresh water generator as described above, the cleaning method according to the fresh water generation method of the present invention is performed, for example, as follows.

  First, the raw water valve 3 and the filtrate water valve 5 are closed, the raw water supply pump 2 is stopped, and the filtration process of the microfiltration membrane / ultrafiltration membrane module 4 is stopped. Thereafter, the air vent valve 15 and the drain valve 14 are opened, and the water on the primary side of the separation membrane of the microfiltration membrane / ultrafiltration membrane module 4 is removed from the lower side of the primary side of the separation membrane of the microfiltration membrane / ultrafiltration membrane module 4. When the water is discharged out of the system through the drain valve 14, the water level in the microfiltration membrane / ultrafiltration membrane module 4 is lowered, and the periphery of the membrane primary side becomes a gas state. Here, the primary side of the separation membrane is the side that supplies the raw water to be filtered, and the secondary side of the separation membrane is the side where the membrane filtered water obtained by filtering the raw water through the membrane is present. Say. Thus, after discharging the total amount of water on the separation membrane primary side of the microfiltration membrane / ultrafiltration membrane module 4, the drainage valve 14 is closed, the flush valve 11 is opened, and the raw water supply pump 2 is operated. The raw water is automatically mixed with air by passing through the aspirator 12. The gas-liquid mixed fluid of raw water and air is supplied to the lower part of the separation membrane primary side of the microfiltration membrane / ultrafiltration membrane module 4 through the check valve 13. The aspirator 12 is a T-shaped tube, and one of the tubes corresponding to the T-shaped horizontal line is connected to the raw water supply pump 2 side, and the other is connected to the microfiltration membrane / ultrafiltration membrane module 4 side. A tube corresponding to a T-shaped vertical line serves as an air suction port. The inside of the pipe corresponding to the horizontal line is partially thinned, and a pipe corresponding to the vertical line branches off from here. When water is flowed in the horizontal direction, the flow rate is increased in the narrowed portion of the pipe, and therefore the pressure is reduced due to the venturi effect. Air is sucked into this depressurized water stream.

  As a result, bubbles are supplied while moving the water level in the microfiltration membrane / ultrafiltration membrane module 4 upward, and the contaminants adhering to the separation membrane surface are effectively peeled off. When the water level in the microfiltration membrane / ultrafiltration membrane module 4 reaches the upper limit, the gas-liquid mixed fluid is located on the upper side surface of the microfiltration membrane / ultrafiltration membrane module 4 together with contaminants separated from the separation membrane surface. The air is discharged from the side nozzle through the air vent valve 15. As the raw water flow rate supplied to the aspirator 12 increases, the air flow rate sucked into the aspirator 12 increases and the contaminants adhering to the surface of the separation membrane are peeled off and removed from the system of the microfiltration membrane / ultrafiltration membrane module 4. Although it is preferable since the effect of discharging is great, it is appropriately set within a range in which the separation membrane is not damaged. The mixing ratio of the raw water flow rate to the air flow rate is preferably about 1: 1 to 5: 1, which has a great effect of removing contaminants.

  Here, in the washing step according to the fresh water generation method of the present invention, as the aspirator supply water to be supplied to the aspirator, any water can be used as long as it does not depart from the gist of the present invention. The raw water may be used as described above with reference to FIG. 1, or the membrane filtrate in the microfiltration membrane / ultrafiltration membrane filtrate storage tank 6 may be used as described later with reference to FIG. . Moreover, you may use water separate from raw | natural water, such as tap water, industrial water, and ground water.

  Depending on the discharge pressure from the aspirator 12 at the time of the above washing, the filtration flow rate is smaller than that in the normal filtration process, but the gas-liquid mixed fluid discharged from the aspirator 12 by opening the filtrate water valve 5 is a microfiltration membrane / limitation. It is also possible to perform filtration while carrying out a cleaning process that supplies the lower part of the outer filtration membrane module 4 on the primary side of the separation membrane. That is, the separation membrane can be washed and filtered at the same time. Further, as described above, the raw water supply pump 2 may not be stopped temporarily, but the raw flush valve 11 and the air vent valve 15 may be opened while the raw water supply pump 2 is in operation, and the raw water valve 3 may be closed. The filtration water valve 5 can be opened and closed arbitrarily.

  Before the gas-liquid mixed fluid is supplied to the lower part of the separation membrane primary side of the microfiltration membrane / ultrafiltration membrane module 4 and / or at the same time, the backwash valve 8 is opened and the backwash pump 7 is operated. When the microfiltration membrane / ultrafiltration membrane filtration water storage tank 6 is backwashed with membrane filtration water, the contaminants are peeled off from the separation membrane surface, and the microfiltration membrane / ultrafiltration membrane module 4 This is preferable because the effect of discharging out of the system is great.

  When the gas-liquid mixed fluid is back-pressure washed before being supplied to the lower part of the separation membrane primary side of the microfiltration membrane / ultrafiltration membrane module 4, the air vent valve 15 and the drain valve 14 are opened to make the precision The water on the primary side of the separation membrane of the filtration membrane / ultrafiltration membrane module 4 is discharged from the lower side of the primary side of the separation membrane of the microfiltration membrane / ultrafiltration membrane module 4 through the drain valve 14 to the outside of the system. It is preferable that the backwash valve 8 is opened and the backwash pump 7 is operated while the drain valve 14 is opened in a state where the side periphery is gas. Since there is no resistance due to water pressure during back pressure washing, suspended substances attached to the surface of the separation membrane are easily separated, and the separated suspended substances are separated from the separation membrane while falling or falling on the surface of the separation membrane. Without staying between the membrane, the microfiltration membrane / ultrafiltration membrane module 4 is discharged from the lower part of the separation membrane primary side through the drain valve 14 to the outside of the system. Thereafter, the backwash valve 8 is closed, the backwash pump 7 is stopped, the drain valve 14 is closed, the air wash valve 11 is opened, the raw water supply pump 2 is operated, and washing with the gas-liquid mixed fluid is performed. To implement.

  On the other hand, when the gas-liquid mixed fluid is supplied to the lower part of the separation membrane primary side of the microfiltration membrane / ultrafiltration membrane module 4 and at the same time backwashing, the backwashing valve 8 is kept with the drain valve 14 closed. It is preferable to operate the raw water supply pump 2 and the backwash pump 7 by opening the air washing valve 11 and the air vent valve 15.

  When performing the back pressure cleaning, it is more likely that the oxidizing agent is added to the membrane filtrate used for back pressure cleaning by operating the oxidizing agent supply pump 9 and accumulates on the surface of the separation membrane or in the pores of the separation membrane. This is preferable because it has the effect of decomposing and removing the organic matter. The oxidizing agent may be any of sodium hypochlorite, chlorine dioxide, ozone and the like, but it is preferable to appropriately set the type and concentration of the oxidizing agent according to the membrane material so that chemical degradation of the separation membrane does not proceed.

  Although the effect of separating suspended substances from the separation membrane surface increases as the back-pressure washing flow rate increases, if the flow rate is too high, back pressure is generated on the primary side of the separation membrane, and the suspended matter is separated from the separation membrane surface. May be inhibited. Therefore, it is preferable to appropriately control the flow rate of the back pressure cleaning according to the structure of the microfiltration membrane / ultrafiltration membrane module 4 and the flow rate of the gas-liquid mixed fluid.

  In addition, when the concentration of suspended solids in the raw water is high and the pipe line in the aspirator 12 is likely to be clogged, clear water not containing suspended components may be supplied to the aspirator 12, and preferably the fresh water generator of FIG. In the state where the raw water supply pump 2 is stopped, the backwash valve 8, the air washing valve 11 and the air vent valve 15 are opened, and the backwash pump 7 is operated, so that the microfiltration membrane / ultrafiltration membrane is operated. The membrane filtrate in the filtrate storage tank 6 is supplied to the aspirator 12, and the membrane filtrate discharged from the aspirator 12 and the gas-liquid mixed fluid of air pass through the check valve 13, and the microfiltration membrane / ultrafiltration membrane module 4 is preferably supplied to the lower part of the primary side of the separation membrane 4 and at the same time back pressure cleaning is performed.

  In order to increase the water recovery rate, the gas-liquid discharged from the system through the air vent valve 15 from the side nozzle located on the upper side surface of the microfiltration membrane / ultrafiltration membrane module 4 together with the contaminants separated from the separation membrane surface After at least a part of the mixed fluid flows into the recovery tank 16, it is preferably returned to the separation membrane primary side of the microfiltration membrane / ultrafiltration membrane module 4 such as the raw water storage tank 1. As described above, an oxidizing agent can be added to the membrane filtrate used for back pressure washing. However, when a chemical solution is added at a high concentration, the raw water storage tank 1 is subjected to chemical treatment such as neutralization treatment. It is desirable to return to

  Further, in the fresh water generation method of filtering the membrane filtration water of the microfiltration membrane / ultrafiltration membrane module 4 with the nanofiltration membrane / reverse osmosis membrane module 20 as in the fresh water generator of FIG. 3, in order to increase the water recovery rate. In addition, at least a part of the concentrated water of the nanofiltration membrane / reverse osmosis membrane module 20 is supplied to the aspirator 12, and the gas-liquid mixed fluid discharged from the aspirator 12 is passed through the check valve 13 to the microfiltration membrane / ultraviolet. You may implement the washing | cleaning supplied to the lower part of the separation membrane primary side of the filtration membrane module 4. FIG.

  The concentration of contaminants in the gas-liquid mixed fluid discharged from the side nozzle located on the upper side surface of the microfiltration membrane / ultrafiltration membrane module 4 through the air vent valve 15 together with the contaminants separated from the separation membrane surface is If it is high, it is preferable to provide a sedimentation tank 17 for separating the pollutant and the clear water (supernatant water) after the collection tank 16. As a separation means, in addition to precipitation separation provided with a precipitation tank 17, coagulation precipitation separation, pressurized flotation separation, centrifugation, sand filtration separation, microfiltration / ultrafiltration membrane filtration separation, filter cloth filtration separation , Filtration filter separation, cartridge filter filtration separation, disk filter separation, filter press, belt press, vacuum dewatering, multiple disk dewatering, etc. can be selected, but pollutants have high specific gravity and high sedimentation Therefore, precipitation separation is suitable. Also, precipitation separation is preferable from the viewpoint of equipment cost, processing cost, and the like.

  After that, the backwash valve 8 and the air washing valve 11 are closed, the raw water supply pump 2 and the backwash pump 7 are stopped, and after the washing with the gas-liquid mixed fluid and the back pressure washing are stopped, the drain valve 14 is temporarily stopped. Is opened, and the water on the primary side of the separation membrane of the microfiltration membrane / ultrafiltration membrane module 4 is discharged out of the system, and then the drain valve 14 is closed, the raw water valve 3 is opened, and the raw water supply pump 2 may be used to fill the primary side of the separation membrane of the microfiltration membrane / ultrafiltration membrane module 4 with the raw water, and the raw water supply pump 2 may be opened by directly opening the raw water valve 3 without draining the entire amount. The primary side of the separation membrane of the microfiltration membrane / ultrafiltration membrane module 4 may be filled with raw water.

  After the separation membrane primary side of the microfiltration membrane / ultrafiltration membrane module 4 is filled with water, the filtration water valve 5 is opened and the air vent valve 15 is closed, so that the microfiltration membrane / ultrafiltration membrane module Returning to the filtration step 4, water production can be continued by repeating the above steps.

  The microfiltration membrane / ultrafiltration membrane module 4 can be either an external pressure type or an internal pressure type, but the flow rate of the gas-liquid mixed fluid contacting the separation membrane surface is high, and the cleaning effect of the present invention is exhibited. The internal pressure type is preferred because it is easy. The membrane filtration method may be a total filtration membrane module or a cross-flow filtration membrane module, but a total filtration membrane module is preferred from the viewpoint of low energy consumption. Furthermore, although it may be a pressurization type membrane module or an immersion type membrane module, the pressurization type membrane module is preferable from the viewpoint that a filtration operation with a high flux is possible. Examples of the shape of the microfiltration membrane / ultrafiltration membrane module 4 include, in the case of a pressurized membrane module, a hollow fiber membrane, a tubular membrane, a monolith membrane, or the like housed in a cylindrical or cuboid pressurized container. The position of the supply port is the lower bottom surface or the lower side surface of the membrane module, and the separation membrane is installed vertically so that the membrane filtrate is obtained from the upper portion of the membrane module. In the case of a submerged membrane module, for example, as shown in FIGS. 4 and 5, a part of raw water or membrane filtration water is supplied to an aspirator, and the gas-liquid mixed fluid discharged from the aspirator is used as a microfiltration membrane / ultrafiltration membrane module. As long as the gas-liquid mixed fluid can be supplied from the lower side of the microfiltration membrane / ultrafiltration membrane module 4 so that it can contact the entire membrane surface of the membrane 4, it can be any cylinder, rectangular parallelepiped, sheet type, etc. Can be anywhere.

  In addition, an organic or inorganic flocculant can be added to the raw water supplied to the lower part of the separation membrane primary side of the microfiltration membrane / ultrafiltration membrane module 4 in the filtration step. By adding a flocculant, there is an effect of suppressing membrane fouling and reducing the concentration of organic substances during membrane filtration. As the mechanical flocculant, dimethylamine-based or polyacrylamide-based cationic polymer flocculants can be used. 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 separation membrane used in the microfiltration membrane / ultrafiltration membrane module 4 is not particularly limited as long as it is porous, but depending on the desired quality and amount of treated water, An outer filtration membrane is used, or both are used in combination. For example, if you want to remove turbid components, Escherichia coli, Cryptosporidium, etc., you can use either a microfiltration membrane or an ultrafiltration membrane. Is preferably used.

  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.

  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 method for cleaning a membrane module according to the above-described water production method of the present invention, it is possible to reduce the equipment cost, the installation space of the equipment, and the electricity bill. Since separation and removal can be performed remarkably, in the case of constant flow operation, the membrane filtration differential pressure is more stable for a longer period than in the prior art. However, it is difficult to completely remove the organic matter, and aluminum or iron derived from the flocculant may adhere, or iron or manganese oxidized by the oxidizing agent may gradually precipitate on the surface of the separation membrane. Therefore, when the membrane filtration differential pressure reaches near the pressure limit of the microfiltration membrane / ultrafiltration membrane module 4, it is preferable to carry out high concentration chemical cleaning.

  The chemical used for the chemical cleaning can be selected after appropriately setting the concentration and the retention time so that the separation membrane 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 at least two because the cleaning effect on the organic matter is enhanced. 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.

(Second Embodiment)
Hereinafter, the second embodiment of the present invention will be described in more detail. As shown in FIG. 6, for example, as shown in FIG. 6, the desalination apparatus targeted in the second embodiment of the present invention stores a microfiltration membrane / ultrafiltration membrane filtrate water storing microfiltration membrane / ultrafiltration membrane filtrate water. A tank 6, a nanofiltration membrane / reverse osmosis membrane module 20, and an air washing valve 11 that is opened when supplying a gas-liquid mixed fluid to the lower part of the separation membrane primary side of the nanofiltration membrane / reverse osmosis membrane module 20, Aspirator 12 for supplying air to the microfiltration membrane / ultrafiltration membrane filtered water, a check valve 13 for preventing backflow to the aspirator 12, and water on the separation membrane primary side of the nanofiltration membrane / reverse osmosis membrane module 20 A drain valve 14 that opens when discharged from the lower part, a high-pressure pump 18 that supplies microfiltration membrane / ultrafiltration membrane filtrate to the nanofiltration membrane / reverse osmosis membrane module 20, and a nanofiltration membrane / reverse osmosis membrane module Nanofiltration membrane that opens when 20 membranes are filtered / An osmosis membrane supply water valve 19, a nanofiltration membrane / reverse osmosis membrane concentration water valve 21 for adjusting the concentrated water flow rate of the nanofiltration membrane / reverse osmosis membrane module 20, and a separation membrane of the nanofiltration membrane / reverse osmosis membrane module 20 A nanofiltration membrane / reverse osmosis membrane concentrated water air vent valve 22 that is opened when supplying a gas-liquid mixed fluid to the lower part on the primary side is provided.

  In the above-mentioned fresh water generator, in the normal filtration step, the nanofiltration membrane / reverse osmosis membrane supply water valve 19 is opened, the flush valve 11, the drain valve 14, the nanofiltration membrane / reverse osmosis membrane concentrated water air vent valve 22 By operating the high-pressure pump 18 in the closed state, the microfiltration membrane / ultrafiltration membrane filtrate water stored in the microfiltration membrane / ultrafiltration membrane filtration water storage tank 6 is converted into a nanofiltration membrane / reverse osmosis membrane. Supply to the lower part of the separation membrane primary side of the module 20 and adjust the opening degree of the nanofiltration membrane / reverse osmosis membrane concentrated water valve 21 to perform pressure cross flow filtration of the nanofiltration membrane / reverse osmosis membrane module 20. . The ratio of the membrane filtrate flow rate and the concentrated water flow rate of the nanofiltration membrane / reverse osmosis membrane module 20 is preferably set as appropriate according to the raw water quality.

  The raw water of the nanofiltration membrane / reverse osmosis membrane module 20 may be clear water with low turbidity, and is not limited to microfiltration membrane / ultrafiltration membrane filtration water as in the above example.

The filtration time is preferably set as appropriate according to the raw water quality, membrane permeation flux, etc., but in the case of constant flow filtration, the predetermined membrane filtration differential pressure or membrane filtration water volume [m ³ ], in the case of constant pressure filtration, The filtration time may be continued until a predetermined membrane filtration flow rate [m ³ / day] or membrane filtration water amount [m ³ ] is reached. The membrane filtration flow rate is the amount of membrane filtration water per unit time.

  In the fresh water generator as described above, the cleaning method of the present invention is performed, for example, as follows.

  First, the nanofiltration membrane / reverse osmosis membrane supply water valve 19 is closed, the high-pressure pump 18 is stopped, and the filtration process of the nanofiltration membrane / reverse osmosis membrane module 20 is stopped. Thereafter, the drain valve 14 and the nanofiltration membrane / reverse osmosis membrane concentrated water air release valve 22 are opened, and the water on the separation membrane primary side of the nanofiltration membrane / reverse osmosis membrane module 20 is removed from the nanofiltration membrane / reverse osmosis membrane module 20. When discharged to the outside of the system through the lower drain valve 14, the water level in the nanofiltration membrane / reverse osmosis membrane module 20 is lowered, and the periphery of the separation membrane primary side becomes a gas state. Here, the primary side of the separation membrane is the side that supplies the microfiltration membrane / ultrafiltration membrane filtrate to be filtered, and the secondary side of the separation membrane is the microfiltration membrane / ultrafiltration membrane filtration water. This refers to the side on which membrane filtered water obtained by filtering with a nanofiltration membrane / reverse osmosis membrane is present. In this way, when the total amount of water on the primary side of the separation membrane of the nanofiltration membrane / reverse osmosis membrane module 20 is discharged, the drain valve 14 is closed, the flush valve 11 is opened, and the high pressure pump 18 is operated. Membrane / ultrafiltration membrane filtrate is automatically mixed with air by passing through the aspirator 12. The gas / liquid mixed fluid of the microfiltration membrane / ultrafiltration membrane filtered water and air is supplied to the lower part of the separation membrane primary side of the nanofiltration membrane / reverse osmosis membrane module 20 through the check valve 13. The aspirator 12 is a T-shaped tube, and one of the tubes corresponding to the T-shaped horizontal line is connected to the high-pressure pump 18 side, and the other is connected to the nanofiltration membrane / reverse osmosis membrane module 20 side. A tube corresponding to a T-shaped vertical line serves as an air suction port. The inside of the pipe corresponding to the horizontal line is partially thinned, and a pipe corresponding to the vertical line branches off from here. When water is flowed in the horizontal direction, the flow rate is increased in the narrowed portion of the pipe, and therefore the pressure is reduced due to the venturi effect. Air is sucked into this depressurized water stream.

  Further, the high pressure pump 18 is temporarily stopped to maintain the operation of the high pressure pump 18 without stopping the filtration process, and the nanofiltration membrane / reverse osmosis membrane supply water valve 19 is opened, and the flush valve 11 is set to open. After opening, the nanofiltration membrane / reverse osmosis membrane supply water valve 19 may be closed.

  As a result, bubbles are supplied while moving the water level in the nanofiltration membrane / reverse osmosis membrane module 20 upward, and pollutants such as organic matter and microorganisms adhering to the separation membrane surface are effectively peeled off. The When the water level in the nanofiltration membrane / reverse osmosis membrane module 20 reaches the upper limit, the gas-liquid mixed fluid is mixed with contaminants such as organic substances and microorganisms separated from the surface of the separation membrane, and the upper part of the nanofiltration membrane / reverse osmosis membrane module 20. From the concentrated water pipe located in the, the nanofiltration membrane / reverse osmosis membrane concentrated water air vent valve 22 is discharged out of the system. As the raw water flow rate supplied to the aspirator 12 increases, the air flow rate sucked into the aspirator 12 increases and the contaminants adhering to the separation membrane surface are peeled off and discharged out of the nanofiltration membrane / reverse osmosis membrane module 20 system. This is preferable because it has a large effect, but it is appropriately set within a range in which the separation membrane is not damaged. The mixing ratio of the raw water flow rate to the air flow rate is preferably about 1: 1 to 5: 1, which has a great effect of removing contaminants. Depending on the discharge pressure from the aspirator 12 at the time of the washing, although the filtration flow rate is smaller than that in the normal filtration step, the gas-liquid mixed fluid discharged from the aspirator 12 by opening the filtered water valve 5 is converted into a nanofiltration membrane / reverse. It is also possible to perform filtration while carrying out a cleaning process that supplies the lower part of the permeable membrane module 20 on the primary side of the separation membrane. That is, the separation membrane can be washed and filtered at the same time.

  In addition, when the discharge pressure of the high pressure pump 18 such as seawater desalination is high, it is preferable to control the discharge pressure with an inverter or the like in consideration of the pressure resistance performance of the aspirator 12.

  Further, as shown in FIG. 7, at least a part of the gas-liquid mixed fluid that has passed through the nanofiltration membrane / reverse osmosis membrane concentrated water air vent valve 22 is directly below the separation membrane primary side of the microfiltration membrane / ultrafiltration membrane module 4. It is preferable to wash the microfiltration membrane / ultrafiltration membrane module 4 at the same time because the water recovery rate increases.

  Thereafter, the air washing valve 11 is closed, the high-pressure pump 18 is stopped, and the washing with the gas-liquid mixed fluid is stopped. Then, the drain valve 14 is once opened to open the nanofiltration membrane / reverse osmosis membrane module 20. After all the water on the primary side of the separation membrane has been discharged out of the system, the drain valve 14 is closed, the nanofiltration membrane / reverse osmosis membrane supply water valve 19 is opened, the high-pressure pump 18 is operated, and the microfiltration membrane / The ultrafiltration membrane filtered water may be filled with the primary side of the separation membrane of the nanofiltration membrane / reverse osmosis membrane module 20, and the nanofiltration membrane / reverse osmosis membrane supply water valve 19 is opened as it is without draining the entire amount. Then, the high-pressure pump 18 may be operated so that the microfiltration membrane / ultrafiltration membrane filtrate is filled with the primary side of the separation membrane of the nanofiltration membrane / reverse osmosis membrane module 20.

  After the primary side of the separation membrane of the nanofiltration membrane / reverse osmosis membrane module 20 is filled with water, if the nanofiltration membrane / reverse osmosis membrane concentrated water air release valve 22 is closed, the nanofiltration membrane / reverse osmosis membrane module 20 becomes Returning to the filtration step, the above steps can be repeated to continue the water production.

  The nanofiltration membrane / reverse osmosis membrane used in the nanofiltration membrane / reverse osmosis membrane module 20 includes a component that is partially permeated in the liquid mixture to be separated, such as a solvent that does not allow other components to permeate. A semi-permeable separation membrane capable of osmotic separation, and the desalination rate of the nanofiltration membrane is 5% or more and less than 93% (evaluation conditions NaCl concentration: 500 mg / l, operating pressure: 0.1 MPa), reverse osmosis membrane Is defined as 93% or more (evaluation conditions NaCl concentration: 500 mg / l, operating pressure: 0.1 MPa). The nanofiltration membrane / reverse osmosis membrane may be appropriately selected according to the required water quality and purpose of use of the membrane filtration water. The material can be a polymer material such as cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer. The separation membrane structure also has a dense layer on at least one side of the separation membrane, and an asymmetric separation membrane having fine pores with gradually increasing pore diameters from the dense layer to the inside of the separation membrane or the other side, and the dense layer of the asymmetric separation membrane. There is a composite separation membrane having a very thin separation functional layer formed of another material on the top. Separation membranes include hollow fiber membranes and flat membranes. The present invention can be carried out regardless of the separation membrane material, the separation membrane structure and the separation membrane form, and is effective. However, typical separation membranes include, for example, cellulose acetate type and polyamide type asymmetric separation membranes. In addition, there are composite separation membranes having a separation function layer of polyamide type and polyurea type, and cellulose acetate type asymmetric separation membranes and polyamide type composite separation membranes should be used from the viewpoint of water production, durability, and salt rejection rate. Is preferred.

  Nanofiltration membranes / reverse osmosis membranes with such performance are incorporated into elements such as spirals, tubulars, and plate-and-frames for actual use, and hollow fiber membranes are bundled and incorporated into the elements. However, the present invention does not depend on the form of these reverse osmosis membrane elements.

  In the present invention, the nanofiltration membrane / reverse osmosis membrane module 20 is not limited to a module in which one or several nanofiltration membrane / reverse osmosis membrane elements are housed in a pressure vessel. Including those arranged in parallel. Combination, number, and arrangement can be arbitrarily performed according to the purpose. As the shape of the nanofiltration membrane / reverse osmosis membrane module 20, a spiral type element in which flat membranes are integrated in a cylindrical shape or a hollow fiber membrane cylindrical element in which hollow fiber membranes are integrated in a cylindrical shape is accommodated in a cylindrical pressurized container. Installed vertically so that the separation membrane is in the vertical direction so that the raw water supply port is located at the bottom or side of the bottom of the membrane module and membrane filtrate is obtained from the top of the membrane module .

  According to the membrane module cleaning method of the present invention described above, it is possible to reduce equipment costs, installation space for equipment, and electricity bills, and remarkably peel and remove contaminants attached to the entire separation membrane surface. Therefore, in the case of constant flow operation, the membrane filtration differential pressure is more stable for a longer period than in the prior art. However, organic matter and microorganisms cannot be removed completely, and scales of calcium and magnesium gradually precipitate on the surface of the separation membrane, so that the membrane filtration differential pressure reaches near the pressure limit of the nanofiltration membrane / reverse osmosis membrane module 20. In this case, it is necessary to perform chemical cleaning. Here, the chemical solution used for washing can be selected after appropriately setting the concentration and holding time to such an extent that the separation membrane does not deteriorate. For organic substances, an alkali such as sodium hydroxide or potassium hydroxide is used. The one containing at least one is preferable because the cleaning effect is high, and the one containing at least one acid such as hydrochloric acid, sulfuric acid, nitric acid, citric acid is more effective for the scale of calcium or magnesium. Since it becomes high, it is preferable. For microorganisms, it is preferable to contain at least one of hypochlorous acid, chlorine dioxide, hydrogen peroxide, and chloramine because the cleaning effect is enhanced.

(Example 1)
As shown in FIG. 1, the microfiltration membrane / ultrafiltration membrane module 4 is a hollow fiber ultrafiltration membrane made of polyvinylidene fluoride having a molecular weight cut off of 150,000 Da made by Toray Industries, Inc. .5m ² pressurized membrane modules are installed in parallel in the vertical direction, the raw water valve 3 and the filtered water valve 5 are opened, the raw water supply pump 2 is operated, and an average turbidity of 8 NTU (Nephelometric Turbidity Unit: ratio Turbidimeter turbidity unit), average TOC (Total Organic Carbon) 5 mg / l of sewage secondary treated water was filtered at a membrane filtration flux of 2 m ³ / m ² / day.

After 30 minutes of filtration through the microfiltration membrane / ultrafiltration membrane module 4, the raw water valve 3 and the filtration water valve 5 are closed, the raw water supply pump 2 is stopped, and the microfiltration membrane / ultrafiltration membrane module 4 is filtered. The process was stopped. Thereafter, the drain valve 14 and the air vent valve 15 were opened, the total amount of water on the separation membrane primary side in the microfiltration membrane / ultrafiltration membrane module 4 was discharged, and the drain valve 14 and the air vent valve 15 were opened. The backwash valve 8 is opened, the backwash pump 7 and the oxidant supply pump 9 are operated, and a sodium hypochlorite aqueous solution with a flux of 2.5 m ³ / m ² / day and a chlorine concentration of 10 mg / l. Back pressure washing with was performed for 1 minute. Thereafter, the backwash valve 8 is closed, the backwash pump 7 and the oxidant supply pump 9 are stopped, the drain valve 14 is closed, the air wash valve 11 is opened, the raw water supply pump 2 is operated, And cleaning with a gas-liquid mixed fluid of air was performed for 1 minute. The raw water flow rate at that time was controlled at 20 L / min per membrane module, and the air suction flow rate from the aspirator 12 was controlled at 14 L / min per membrane module. Thereafter, the air flush valve 11 is closed, the raw water supply pump 2 is stopped, the washing with the gas-liquid mixed fluid is stopped, the drain valve 14 is opened, and the inside of the microfiltration membrane / ultrafiltration membrane module 4 is opened. All the water was discharged out of the system. Thereafter, the drain valve 14 is closed, the raw water valve 3 is opened, the raw water supply pump 2 is operated, and the raw water is supplied into the microfiltration membrane / ultrafiltration membrane module 4. The air vent valve 15 was opened, the air vent valve 15 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 microfiltration membrane / ultrafiltration membrane module 4 was stable at 48 kPa after 3 months with respect to 25 kPa immediately after the start of operation, and the chemical solution was not washed. The average daily power consumption was 4.8 kWh / day.

(Example 2)
As shown in FIG. 6, the nanofiltration membrane / reverse osmosis membrane module 20 was loaded with two reverse osmosis membrane elements (TML10F) manufactured by Toray Industries, Inc. having a total element length of 1 m and a membrane area of 8 m ^{2 in} a pressure vessel in series. The thing is installed in the vertical direction, the nanofiltration membrane / reverse osmosis membrane supply water valve 19 is opened, the opening degree of the nanofiltration membrane / reverse osmosis membrane concentrated water valve 21 is adjusted, and the high pressure pump 18 is operated. The ultrafiltration membrane filtrate of Example 1 was subjected to cross-flow filtration at a membrane filtration flow rate of 20 m ³ / day, a concentrated water flow rate of 20 m ³ / day, and a water recovery rate of 50%.

  After filtering with the nanofiltration membrane / reverse osmosis membrane module 20 for 3 hours, the nanofiltration membrane / reverse osmosis membrane supply water valve 19 is closed, the high-pressure pump 18 is stopped, and the nanofiltration membrane / reverse osmosis membrane module 20 The filtration process was stopped. Thereafter, the drain valve 14 and the nanofiltration membrane / reverse osmosis membrane concentrated water air release valve 22 are opened, and the total amount of water on the separation membrane primary side of the nanofiltration membrane / reverse osmosis membrane module 20 is discharged. With the reverse osmosis membrane concentrated water air vent valve 22 open, the drain valve 14 is closed, the flush valve 11 is opened, and the high pressure pump 18 is operated to mix the ultrafiltration membrane filtrate with air-liquid mixture. Washing with fluid was carried out for 10 minutes. At that time, the raw water flow rate was controlled to 20 L / min, and the air suction flow rate from the aspirator 12 was controlled to 10 L / min. Thereafter, the air washing valve 11 is closed, the high-pressure pump 18 is stopped, the washing with the gas-liquid mixed fluid is stopped, the drain valve 14 is opened, and the water in the nanofiltration membrane / reverse osmosis membrane module 20 is opened. Was discharged out of the system. Thereafter, the drain valve 14 is closed, the nanofiltration membrane / reverse osmosis membrane supply water valve 19 is opened, the high-pressure pump 18 is operated, and the ultrafiltration membrane filtrate is supplied to the nanofiltration membrane / reverse osmosis membrane module 20. After the feed, the nanofiltration membrane / reverse osmosis membrane concentrated water air vent valve 22 was closed, the process was returned to the filtration step, and the above steps were repeated.

  As a result, the operation pressure of the nanofiltration membrane / reverse osmosis membrane module 20 was stable at 1.8 MPa even after 3 months with respect to 1.6 MPa immediately after the start of operation, and no chemical cleaning was performed. The average daily power consumption was 36.7 kWh / day.

(Comparative Example 1)
As shown in FIG. 8, instead of operating the raw water supply pump 2 and the aspirator 12 to perform the cleaning with the gas-liquid mixed fluid of raw water and air, the raw water supply pump 2 and the air blower / compressor 23 are operated to Except for cleaning with a gas-liquid mixed fluid, the procedure was exactly the same as Example 1. As the air blower / compressor 23, a compressor (LH300FS) manufactured by Hitachi Industrial Equipment Systems Co., Ltd. was used.

  As a result, the membrane filtration differential pressure of the microfiltration membrane / ultrafiltration membrane module 4 was stable at 48 kPa after 3 months with respect to 25 kPa immediately after the start of operation, and the chemical solution was not washed. Moreover, the average daily power consumption was 5.1 kWh / day, which was higher than that of Example 1.

(Comparative Example 2)
Except for installing the microfiltration membrane / ultrafiltration membrane module 4 in the vertical method, it was exactly the same as Example 1 except that it was installed horizontally.

  As a result, the membrane filtration pressure difference of the microfiltration membrane / ultrafiltration membrane module 4 reached 100 kPa after 18 days with respect to 25 kPa immediately after the start of operation, and had to be washed with a chemical solution. The average daily power consumption was 8.9 kWh / day, which was higher than that of Example 1.

(Comparative Example 3)
As shown in FIG. 9, instead of operating the high-pressure pump 18 and the aspirator 12 to perform cleaning with the gas-liquid mixed fluid of raw water and air, the high-pressure pump 18 and the air blower / compressor 23 are operated to operate the gas-liquid of the raw water and air. Except for cleaning with a mixed fluid, the procedure was exactly the same as in Example 2. As the air blower / compressor 23, a compressor (0.75OP-9.5GSB5 / 6) manufactured by Hitachi Industrial Equipment Systems Co., Ltd. was used.

  As a result, the operation pressure of the nanofiltration membrane / reverse osmosis membrane module 20 was stable at 1.8 MPa even after 3 months with respect to 1.6 MPa immediately after the start of operation, and no chemical cleaning was performed. Moreover, the average daily power consumption was 37.2 kWh / day, which was higher than Example 1.

(Comparative Example 4)
Except that the nanofiltration membrane / reverse osmosis membrane module 20 was not installed in the vertical direction but installed horizontally, it was exactly the same as Example 2.

  As a result, the operating pressure of the nanofiltration membrane / reverse osmosis membrane module 20 increased to 2.4 MPa immediately after the start of operation, and increased to 2.4 MPa after 3 months, and had to be washed with a chemical solution. Moreover, the average daily power consumption was 42.1 kWh / day, which was higher than Example 2.

1: Raw water storage tank 2: Raw water supply pump 3: Raw water valve 4: Microfiltration membrane / ultrafiltration membrane module 5: Filtration water valve 6: Microfiltration membrane / ultrafiltration membrane filtration water storage tank 7: Backwash pump 8 : Backwash valve 9: Oxidant supply pump 10: Oxidant storage tank 11: Air washing valve 12: Aspirator 13: Check valve 14: Drain valve 15: Air vent valve 16: Collection tank 17: Settling tank 18: High pressure pump 19: Nanofiltration membrane / reverse osmosis membrane supply water valve 20: Nanofiltration membrane / reverse osmosis membrane module 21: Nanofiltration membrane / reverse osmosis membrane concentrated water valve 22: Nanofiltration membrane / reverse osmosis membrane concentrated water air release valve 23: Air blower / compressor

Claims (15)

  The raw water is supplied to the lower part of the separation membrane primary side of the membrane module installed so that the separation membrane is in the vertical direction, and the raw water is filtered by the separation membrane to obtain the membrane filtrate from the separation membrane secondary side. A fresh water generation method comprising: temporarily performing a cleaning step of supplying aspirator supply water to an aspirator and supplying a gas-liquid mixed fluid discharged from the aspirator to a lower portion of the separation membrane primary side of the membrane module. A method for producing fresh water.   The fresh water generation method according to claim 1, wherein at least a part of the aspirator feed water is raw water or membrane filtered water.   The fresh water generation method according to claim 1 or 2, wherein water on the separation membrane primary side of the membrane module is discharged out of the system before supplying a gas-liquid mixed fluid to a lower portion of the separation membrane primary side of the membrane module. .   The gas-liquid mixed fluid is supplied to a lower part of the separation membrane primary side of the membrane module, and at least a part of the water discharged from the separation membrane primary side of the membrane module is recovered and mixed with the raw water. Item 4. A fresh water generation method according to any one of Items 1 to 3.   The fresh water generation method according to claim 4, wherein the water discharged from the primary side of the separation membrane of the collected membrane module is separated into suspended matter and clarified water, and the clarified water is mixed with the raw water.   The fresh water generation method according to any one of claims 1 to 5, wherein the separation membrane is a microfiltration membrane or an ultrafiltration membrane.   Before and / or simultaneously with supplying the gas-liquid mixed fluid to the lower part of the separation membrane primary side of the membrane module, the membrane filtrate is fed from the separation membrane secondary side of the membrane module to the separation membrane primary of the membrane module. The fresh water generation method of Claim 6 which implements the back pressure washing | cleaning pumped to the side.   The fresh water generation method according to claim 7, wherein an oxidizing agent is added to the membrane filtrate when performing back pressure washing.   The membrane filtration water is supplied to a nanofiltration membrane module or a reverse osmosis membrane module to be separated into permeated water and concentrated water, and at least a part of the concentrated water is used as an aspirator supply water. The fresh water generation method in any one of -8.   The fresh water generation method according to any one of claims 1 to 5, wherein the separation membrane is a nanofiltration membrane or a reverse osmosis membrane.   Before supplying the raw water to the lower part of the separation membrane primary side of the membrane module, membrane filtration is performed with a microfiltration membrane module or an ultrafiltration membrane module, which is a second membrane module installed in the previous stage of the membrane module, The fresh water generation method according to claim 10.   The gas-liquid mixed fluid is supplied to the lower part of the separation membrane primary side of the membrane module, and at least a part of the water discharged from the separation membrane primary side of the membrane module is recovered, and the second membrane module The fresh water generation method according to claim 11 to supply.   A membrane module that filters raw water through a separation membrane installed in a vertical direction and discharges membrane filtrate from the secondary side of the separation membrane, and a raw water supply unit that supplies raw water to the lower part of the separation membrane primary side of the membrane module An aspirator that mixes a part of the aspirator supply water and gas and supplies a gas-liquid mixed fluid to the lower part of the separation membrane primary side of the membrane module, and an aspirator supply water supply that supplies the aspirator supply water to the aspirator A fresh water generator comprising a unit.   A raw water supply pipe for supplying the raw water to the lower part of the separation membrane primary side of the membrane module is branched, and the aspirator supply water supply unit supplies the raw water as the aspirator supply water to the aspirator. The fresh water generator according to claim 13.   The membrane filtrate discharge pipe from which the membrane filtrate is discharged from the separation membrane secondary side of the membrane module is branched, and the aspirator supply water supply unit supplies the membrane filtrate to the aspirator as the aspirator supply water. The fresh water generator according to claim 13, wherein the fresh water generator is supplied.

Images