JP2011083764A - Method for operating water purification system and water purification system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a water purification system which can effectively prevent fouling and clogging of a membrane module and can perform stable filtering operation for a long period of time. <P>SOLUTION: The method for operating the water purification system includes: pressurizing water by a water supply pump to supply it to the membrane module; and performing membrane filtration in the water purification system using the membrane module. In the method, super fine bubbles are generated underwater after pressurization by the water supply pump and before supply to the membrane module. Water to be supplied to the water supply pump may be raw water and/or concentrated circulating water from the membrane module. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a water purification system operation method and a water purification system, and more particularly, to a water purification system operation method and a water purification system capable of reducing filtration operation energy and effectively preventing clogging of a membrane module.

  In place of the conventional water purification system that has undergone a coagulation-precipitation-sand filtration-chlorine sterilization process, a water purification system to which membrane separation technology is applied has attracted attention. For example, cross flow filtration using an ultrafiltration membrane or a microfiltration membrane has been tried. Cross-flow filtration means that the raw water is supplied to one membrane surface (raw water supply side separation membrane surface) of the separation membrane, and the permeated water that has permeated through the separation membrane is the other membrane surface (permeated water side separation membrane surface) of the separation membrane The filtration method has the effect of stripping off turbid substances contained in the raw water adhering to the separation membrane surface by flowing raw water parallel to the separation membrane surface of the raw water supply side when collecting from the membrane. Say. However, even with cross-flow filtration, turbid substances contained in the raw water are laminated on the surface of the separation membrane as the filtration time elapses, resulting in clogging of the separation membrane.

  This clogging not only increases the filtration operation energy of the water purification system, but also causes operation interruption. Therefore, as a method for eliminating or preventing this clogging, it is generally called back pressure washing (hereinafter referred to as “back washing”). In order to enable long-term use of the separation membrane, the backwash frequency, backwash time, etc. are changed based on various changes such as raw water turbidity, permeated water amount, permeated water pressure, etc. A method has been proposed. For example, backwashing in cross-flow filtration involves regular backwashing depending on the raw water turbidity, changing the membrane backwashing conditions when the filtration rate tends to decrease due to fluctuations in water quality and filtration rate, A method is known in which the frequency of backwashing is adjusted according to the variation in the degree, the risk of closing the separation membrane is eliminated, and the recovery rate of water is increased. In these methods, when turbid substances adhere to the raw water side separation membrane surface, the raw water pressure on the raw water supply side rises due to clogging, so the pressure several times the increased pressure is set as the backwash pressure. Used to remove turbid substances. Therefore, a high pressure is always applied to the separation membrane, which may shorten the useful life of the separation membrane. Moreover, the high pressure load extends not only to the separation membrane but also to the pump used.

  Therefore, there is a demand for the development of a backwashing method that improves backwashing efficiency, relaxes the conditions for using expensive separation membrane modules, and can easily cope with various water purification systems. Patent Document 1 discloses that a pause process of the filtration process is provided immediately before or after backwashing, and that backwashing water containing a bactericidal agent is used. Patent Document 2 discloses a filtration membrane cleaning method that includes a backwash treatment step, a hypochlorite injection immersion step, and a sulfuric acid injection immersion step, and an immersion cleaning time of 10 to 60 minutes. However, in these methods, it is essential to use a chemical solution, and the operation is complicated, and it is not necessarily an industrially efficient water purification system.

  As a membrane cleaning system using microbubbles, Patent Document 3 discloses a membrane purification system that activates a microbubble generator during a cleaning operation of a reverse osmosis membrane. This is a method for generating microbubbles during membrane cleaning. The efficiency of the membrane filtration operation is not improved so much. Patent Document 4 discloses a method of cleaning a hollow fiber membrane module using fine bubbles. This method is a method of supersaturating a gas in membrane filtrate water during membrane cleaning to generate fine bubbles. Since it is not generated in water, a sufficient cleaning effect cannot be obtained, and at the same time, membrane filtration water is used as cleaning water, resulting in a decrease in filtration recovery rate.

  Non-Patent Document 1 uses a device comprising a nitrogen cylinder, a control unit, a pressure vessel, a microbubble generator, a pump and a stirrer, and nitrogen gas is introduced into a pressure vessel containing purified water having a salt concentration of 1%. A method of applying pressure, rotating with a stirrer, driving a pump to generate microbubbles in salt water, permeating the RO membrane, and recovering fresh water has been proposed. However, in this method, since air accumulates above the pressure vessel, in order to remove this and keep the liquid flow rate stable, while supplying nitrogen gas from a nitrogen cylinder into the pressure vessel and discharging excess bubbles, The pressure in the pressure vessel is controlled by the control unit. For this reason, the apparatus becomes complicated and the operation becomes complicated.

JP-A-8-197053 Japanese Patent Laid-Open No. 2005-87887 JP 2006-263501 A JP 2003-251157 A

Proceedings of Annual Meeting of Multiphase Society 2009 (Kumamoto University) Proceedings, 218-219

An object of the present invention is to provide a water purification system operation method and a water purification system that can effectively prevent the membrane module from being soiled and clogged, and can perform a filtration operation at a high filtration rate that is efficient and stable for a long period of time. It is in.
Another object of the present invention is to provide a method for operating a water purification system and a water purification system that do not require complicated operations and that can perform a filtration operation at a stable high filtration rate for a long period of time without using chemicals. It is in.

  As a result of intensive investigations to achieve the above object, the present inventor, after having pressurized raw water (or concentrated circulating water from the membrane module) with a water supply pump in a water purification system using a membrane module, When ultrafine bubbles are generated in (or concentrated circulating water from the membrane module), the raw water (or concentrated circulating water from the membrane module) is supplied to the membrane module by the supply pump, and membrane filtration is performed. The action of air bubbles can effectively prevent the membrane module from being soiled and clogged, and can greatly reduce the frequency and time of backwashing. Therefore, it is efficient and stable for a long time without complicated operations. The present inventors have found that a filtration operation at a filtration rate can be performed, thereby completing the present invention.

  That is, the present invention is a water purification system that uses a membrane module, pressurizes water with a water supply pump, and supplies the membrane module with membrane filtration to perform membrane filtration. Provided is a method for operating a water purification system, characterized by generating ultrafine bubbles in water after pressurization and before supplying a membrane module, and supplying a liquid containing the ultrafine bubbles to the membrane module.

  In the operation method of the water purification system, the water supplied to the water supply pump may be raw water and / or concentrated circulating water from the membrane module.

  In addition, the water supplied to the water supply pump is clean water and / or permeated water from the membrane module, and after the liquid containing ultrafine bubbles is used for cleaning the device or apparatus to be cleaned, after use The cleaning liquid may be supplied to the membrane module.

  Further, the gas-liquid mixed fluid obtained by mixing the gas with water is circulated through the flow path having the reduction part, the most sandwiched part, and the expansion part by the high pressure by the water supply pump, and the gas formed in the flow path is obtained. Ultra fine bubbles mainly having a size of 50 μm or less may be generated by changing the flow velocity and pressure of the high-speed shear flow of the liquid mixed fluid.

  It is preferable that the filtration pressure when performing membrane filtration by the membrane module by pressurizing water with a water supply pump is 0.01 MPa (gauge pressure) or more.

  As a membrane filtration method in the membrane module, a cross flow filtration method is preferable. Examples of the membrane module include an ultrafiltration membrane module, a microfiltration membrane module, a nanofiltration membrane module, and a reverse osmosis membrane module. Among these, an ultrafiltration membrane module and a microfiltration membrane module are preferable.

  In the above operation method, the membrane module may be subjected to intermittent backwashing with permeated water from the membrane module or separately supplied clean water.

  The present invention also provides a water purification system using a membrane module, a water supply pump for supplying water to the membrane module, a gas supply means for supplying gas into the water supply line, and a gas mixed in the water. The flow rate of the high-speed shear flow of the gas-liquid mixed fluid formed in the flow path is made to flow through the flow path having the reduced part, the most sandwiched part, and the enlarged part by high pressure from the water supply pump. A water purification system is provided that includes ultrafine bubble generating means for generating ultrafine bubbles in water by changing the pressure.

  In this water purification system, the water supplied to the water supply pump may be raw water and / or concentrated circulating water from the membrane module.

  Further, the water supplied to the water supply pump is clean water and / or permeated water from the membrane module, and is equipped with a device or apparatus to be cleaned that is cleaned with a liquid containing ultrafine bubbles. The liquid after washing of the device or apparatus may be supplied to the membrane module.

  Moreover, it is preferable that the gas supply means is provided immediately before the water supply pump.

  The water purification system may further include a cleaning unit that intermittently backwashes the membrane module.

  This water purification system may further be provided with a prefilter for removing contaminants of the raw water.

  Note that the operation method of the water purification system of the present invention does not include a method of simply cleaning the membrane module without obtaining permeated water (filtered water; product). In addition, the water purification system of the present invention does not include an apparatus that simply cleans the membrane module without obtaining permeated water (filtered water; product). The present invention includes a method and a system in which permeated water (filtered water) is used for cleaning a device or apparatus to be cleaned, and the water after being used for cleaning is purified by a membrane module.

  According to the water purification system operation method and water purification system of the present invention, the membrane module can be effectively prevented from being contaminated and clogged, and can be efficiently and stably filtered at a high filtration rate for a long period of time. . In addition, the frequency and time of backwashing can be reduced, no complicated operation is required, and a stable high filtration rate can be performed for a long period of time without using chemicals. Furthermore, since the recovery rate of filtered water can be increased, the number of backwashes can be reduced.

It is a schematic explanatory drawing (schematic flowchart) which shows an example of the operating method of the water purification system of this invention. It is a schematic explanatory drawing (schematic flowchart) which shows the other example of the operating method of the water purification system of this invention. It is sectional drawing which shows an example of the ultrafine bubble generator used by the method of this invention. It is a fragmentary sectional view (sectional view of a liquid feeding dispersion part) showing an example of a device (water pump with a built-in ultrafine bubble generator) in which a water pump used in the method of the present invention and an ultrafine bubble generator are integrated. . It is the elements on larger scale (sectional drawing) of the storage chamber of the water pump with a built-in ultrafine bubble generator of FIG. It is sectional drawing which shows the other example of the apparatus (water pump with a built-in ultrafine bubble generator) with which the water pump used by the method of this invention and the ultrafine bubble generator were integrated. It is the elements on larger scale (sectional drawing) of the water pump with a built-in ultrafine bubble generator of FIG. It is sectional drawing which shows the further another example of the apparatus (water pump with a built-in ultrafine bubble generator) in which the water pump and the ultrafine bubble generator used by the method of this invention were integrated. It is a graph which shows the relationship between the operation days in Example 1, and an actual flux. It is a graph which shows the relationship between the elapsed time in Example 2, and the filtration flow rate. It is a schematic explanatory drawing (schematic flowchart) which shows the further another example of the operating method of the water purification system of this invention.

  In the operation method of the water purification system of the present invention, water is pressurized by a water supply pump, and ultrafine bubbles are generated in the water after being pressurized by the water supply pump and before the membrane module is supplied. Membrane filtration is performed by supplying a solution containing

  In one embodiment of the present invention, raw water and / or concentrated circulating water from a membrane module (hereinafter, “concentrated circulating water from a membrane module” may be simply referred to as “concentrated circulating water”) is supplied by a water supply pump. After pressurization by the water supply pump and before supply of the membrane module, ultrafine bubbles are generated in the concentrated water from the raw water and / or the membrane module, and the liquid containing the ultrafine bubbles is removed from the membrane module. The membrane is filtered and the water is purified.

  The raw water subjected to membrane filtration is not particularly limited, and includes fresh water (river water, lake water, etc.), seawater, and the like.

  In another aspect of the present invention, clean water and / or permeated water (filtered water) from the membrane module is pressurized by a water supply pump, and after being pressurized by the water supply pump and before the membrane module is supplied. After generation of ultrafine bubbles in clean water and / or permeated water (filtered water) from the membrane module, the ultrafine bubble-containing liquid obtained in this way is used for cleaning the equipment or device to be cleaned, and after the obtained use The cleaning liquid is supplied to the membrane module, membrane filtration is performed, and water is purified.

  Examples of the apparatus or apparatus to be cleaned include tanks, reactors, piping, heat exchangers, distillation towers, extraction towers, packed towers, containers, membrane modules, filters, and spinning nozzles.

  In the present invention, the filtration membrane is not particularly limited, and examples thereof include an ultrafiltration membrane, a microfiltration membrane, a nanofiltration membrane, and a reverse osmosis membrane. The ultrafiltration (UF) membrane is a separation membrane for separating a substance having a molecular weight of 500 to 300,000 (molecular size of about 0.001 to 0.03 μm), and includes a category of a normal nanofiltration membrane. A microfiltration (MF) membrane is a separation membrane for separating particles having a particle size of 0.02 to 2 μm. Accordingly, the pore diameter of the ultrafiltration or microfiltration membrane is 0.001 to 2 μm, more preferably 0.01 to 1 μm. A reverse osmosis (RO) membrane is a separation membrane (with a molecular size of about 1 to 0.001 μm) for separation of salts and substances having a molecular weight of about 500, and is used for desalination of seawater, for example. Further, the permeated water of the ultrafiltration membrane may be passed through the reverse osmosis membrane.

  The membrane module may be any of a hollow fiber filtration membrane module, a flat plate module, a tubular module, a spiral module, etc., but a hollow fiber filtration membrane module is preferable because it can be backwashed relatively easily. . The hollow fiber membrane inner diameter of the hollow fiber membrane module is such that fine bubbles having a bubble diameter of 50 μm or less are effectively passed through the inside of the hollow fiber membrane, while preventing the blocking of contaminants and improving the hollow fiber filling rate. Therefore, the range of about 0.1 to 2.0 mm is preferable, and the range of 0.5 to 1.0 mm is more preferable. The membrane module includes a filter using a membrane filter.

  Examples of the material for the separation membrane include general materials such as cellulose acetate, polyacrylonitrile, polysulfone, polyethersulfone, polyacrylonitrile, aromatic polyamide, polyvinylidene fluoride, polyvinyl chloride, polyethylene, polypropylene, polyimide, and ceramic. Can be used. Among these, cellulose acetate, polysulfone, polyethersulfone, polyacrylonitrile, and aromatic polyamide are preferable as the material for the ultrafiltration membrane, and polyvinylidene fluoride, polyethylene, polypropylene, polysulfone, and ceramic are preferable as the material for the microfiltration membrane. . As a material for the reverse osmosis membrane, cellulose acetate, aromatic polyamide and the like are preferable.

  Examples of the hollow fiber membrane include cellulose acetate-based hollow fiber membranes, polysulfone-based hollow fiber membranes, polyacrylonitrile-based hollow fiber membranes, and polyvinylidene fluoride hollow fiber membranes. The cellulose acetate-based hollow fiber membrane is preferable because it can be easily suppressed and fouling of the membrane is easily suppressed. In addition, a pore having a smaller pore diameter on the inner surface side than on the outer surface side is suitable as the internal pressure type.

  In the present specification, ultrafine bubbles refer to bubbles having a bubble diameter of 50 μm or less when they are generated. The bubble diameter is preferably 50 μm or less when generated, and more preferably 10 μm or less when generated. Even when the ultrafine bubbles are generated, for example, about 10 μm, there is a phenomenon that they gradually decrease with time. In the present invention, the number of bubbles having a bubble diameter of 2 to 50 μm (the number measured by a particle counter) contained in ultrafine bubble-containing water (such as ultrafine bubble-containing raw water) flowing into the membrane module is 20 to 30. At ° C., for example, 100 / mL or more, preferably 300 / mL or more, more preferably 1000 / mL or more, and particularly preferably 2000 / mL or more. The use of ultrafine bubbles can prevent the membrane surface of the membrane module from becoming dirty and clogging the membrane pores. In particular, the effect of preventing clogging of the pores of the membrane is great. The ultrafine bubble-containing water (such as ultrafine bubble-containing raw water) that flows into the membrane module may contain bubbles having a bubble diameter of 50 μm or more. Such bubbles also contribute to prevention of contamination on the membrane surface of the membrane module. It is assumed that the ultrafine bubbles act to remove the dirt on the film surface, cause the dirt to be adsorbed on the surface of the foam, and not adhere to the film surface again.

  Giving high-speed shearing to a gas-liquid mixed fluid in which gas as an ultrafine bubble source is mixed in water (raw water or concentrated circulating water), or circulating the gas-liquid mixed fluid through a flow path in which the gap changes, An ultra-fine bubble generator that generates bubbles of a size of 50 μm or less by changing the flow velocity and pressure of the gas-liquid mixed fluid by changing the gap of the channel (for example, 70% or more of all the generated bubbles have a bubble diameter of An ultrafine bubble generating device that is a bubble of 50 μm or less can be used. As a method for generating ultrafine bubbles, generally, a method using a chemical, a method in which a gas is dissolved in a supersaturated state and a pressure is reduced, a method in which a gas is mixed with a fluid to give high-speed shearing, a flow of a gas-liquid mixed fluid There is a method of changing the flow gap and pressure of the gas-liquid mixed fluid by changing the passage gap. It is generally known that the properties of the generated ultrafine bubbles differ greatly depending on the generation method of the ultrafine bubbles (Hirofumi Taisei: All of microbubbles, Nihon Jitsugyo Shuppan pp. 1-285, 2006). Ultrafine bubbles can be generated by mixing gas in water (raw water or concentrated circulating water) to give high-speed shear, or by changing the flow gap of the gas-liquid mixed fluid to change the gas-liquid mixed fluid. A method of changing the flow rate and pressure is preferred. As a method for applying high-speed shearing, there are a method of generating bubbles by rotating a liquid and a gas at a high speed in a cylindrical shape, and a method of generating bubbles by passing a gas-liquid mixed fluid through an annular slit at a high speed. . In particular, an apparatus including an annular slit that generates ultrafine bubbles in the liquid by allowing the gas-liquid mixed fluid to pass through the annular slit and ejecting the fluid is suitable. This annular slit is preferably provided with a flow path expanding portion provided so as to expand from the minimum gap portion from the inner diameter side to the outer diameter side (in this case, the gas-liquid mixed fluid flows from the inner diameter side to the outer diameter. Flows towards the side). The annular slit may be provided with a flow passage expanding portion provided so as to expand from the smallest gap portion from the outer diameter side toward the inner diameter side (in this case, the gas-liquid mixed fluid is outside It flows from the diameter side toward the inner diameter side). When the gas-liquid mixed fluid is caused to pass through the annular slit to be ejected, the annular slit may be passed using high pressure generated by high-speed rotation of a rotating body provided with a centrifugal blade. Further, as a method of changing the flow velocity and pressure of the gas-liquid mixed fluid by changing the channel gap of the gas-liquid mixed fluid, for example, the gas-liquid mixed fluid can be reduced by using a high pressure to reduce the narrowing portion, Examples thereof include a method of circulating a flow path (for example, an annular slit). In the present invention, water containing ultrafine bubbles (raw water and / or concentrated circulating water from the membrane module) can be supplied to the membrane module without performing pressure control with gas.

  In the present invention, after the pressurization with the water supply pump (raw water supply pump and / or concentrated circulating water supply pump, etc.) (more specifically, after pressurization by the rotation of the pump impeller of the water supply pump), the ultrafine bubbles It is important to perform pressure membrane filtration with the water supply pump while generating water. The ultrafine bubbles generated in a state where the pressure is increased by the water supply pump expands due to the pressure drop when passing through the membrane, and the pressure when the gas dissolved under high pressure flows through the membrane (and membrane pores) Since an extremely large number of ultrafine bubbles are generated by the descending, the membrane module can be effectively prevented from being stained and clogged. When using an ultrafiltration membrane or a microfiltration membrane module, the pressure on the discharge side of the water supply pump (that is, the filtration pressure at the time of membrane filtration) is, for example, 0.01 MPa (gauge pressure) or more [for example, 0.01 to 0.1 MPa (Gauge pressure)], preferably 0.02 MPa (gauge pressure) or more [for example, 0.02 to 0.08 MPa (gauge pressure)]. When a reverse osmosis membrane module is used as the membrane module, the pressure on the discharge side of the water supply pump is about 100 times higher than that of the ultrafiltration or microfiltration membrane module. This is [for example, 1 to 7 MPa (gauge pressure)], and a high-pressure pump is required. In addition, it is not necessary to perform pressure control with gas, and it is possible to generate ultrafine bubbles and supply membrane supply water containing the ultrafine bubbles to the membrane module by pressurizing only a normal water supply pump. The water can be purified without performing complicated operations.

The introduction position of the gas (air or the like) serving as the ultrafine bubble source (the location where the gas supply means is installed) is not particularly limited as long as it is upstream of the membrane module and the apparatus (ultrafine bubble generation means) that generates the ultrafine bubbles. However, it is upstream of the water supply pump (before pressurization due to rotation of the pump impeller) in that the introduced gas and water (raw water, etc.) can be efficiently mixed with the rotary blades of the water supply pump. In particular, it is particularly preferable to be immediately before the water supply pump (immediately before pressurization by rotation of the pump impeller). The gas supply amount is, for example, 0.005 to 0.50 L / min (standard state), preferably 0.03 to 0.30 L / min (standard state) per 1 m ³ / h of the discharge flow rate of the water supply pump, Preferably, it is 0.05-0.30 L / min (standard state). If the amount of gas supplied is too small, the number of ultrafine bubbles will decrease, and if it is too large, the proportion of ultrafine bubbles with a size of 50 μm or more will increase, and both will effectively remove membrane module contamination and clogging. It cannot be prevented. Even if the gas supply amount is small, a certain degree of effect can be obtained if ultrafine bubbles are generated.

  The membrane filtration method in the membrane module can be selected as appropriate according to the structure of the module, and may be either a total filtration method or a cross-flow filtration method, but suspended matter or colloid in the membrane supply water is deposited on the membrane surface. The internal pressure type cross-flow filtration method is particularly preferable in that the phenomenon can be suppressed.

  In the case of the cross flow filtration method, the higher the linear velocity of the membrane surface of water (raw water, etc.), the more the deposition of adhering substances on the membrane surface is suppressed, so a higher filtration flux (flux) is obtained, and in terms of preventing membrane contamination. Although it is preferable, the running cost increases as the film surface speed increases. According to the present invention, since water (raw water, etc.) containing ultrafine bubbles is supplied to the membrane module, substances adhering to the membrane surface and pores can be obtained without increasing the film surface linear velocity of water (raw water, etc.) so much. Can be suppressed. Therefore, energy can be reduced and running cost can be reduced. In the present invention, the membrane surface linear velocity (cross flow velocity) of water (raw water, etc.) in the cross flow filtration method is, for example, 0.02 m / s or more and less than 0.5 m / s, preferably 0.05 m / s or more. It is less than 0.2 m / s.

In the method of the present invention, in order to prevent deposition of adhering substances on the membrane surface and perform membrane filtration operation for a long period of time, the membrane module is intermittently treated with permeated water from the membrane module or clean water supplied separately. Back washing is preferably performed. The backwashing is preferably performed at a predetermined cycle while controlling the pressure. The frequency of backwashing is preferably once every 0.5 to 3 hours. The backwashing time is preferably 0.5 to 2 minutes. At this time, the filtration recovery rate may be set to 90% or more, more preferably 95% or more. The filtration recovery rate is expressed by the following formula. In the method of the present invention, since the filtration recovery rate can be increased, the number of backwashing (frequency) can be reduced.
Filtration recovery rate = 100 × (membrane filtration flow rate−backwash water amount) / membrane filtration flow rate

  In addition, you may add chemical | medical agents, such as disinfectants, such as sodium hypochlorite, to the washing water used for backwashing as needed.

  According to the present invention, since water (raw water, etc.) containing ultrafine bubbles is supplied to the membrane module, it is possible not only to suppress deposition of adhered substances on the membrane surface, but also to clogged suspended matter etc. in the membrane pores. Since the phenomenon can be effectively prevented, the frequency and time of backwashing can be greatly reduced, and the industrial significance is extremely large in terms of improving the filtration recovery rate, improving operability, and reducing energy costs. It is.

  In the method of the present invention, it is preferable that bubbles larger than the pore diameter of the filtration membrane are confirmed on the permeate side of the membrane module (for example, ultrafiltration membrane module, microfiltration membrane module). When ultrafine bubbles are generated, for example, even if the bubble diameter is 10 μm, it gradually shrinks with time, and eventually shrinks to nano size, so that these bubbles can permeate inside the membrane pores and wash inside the membrane pores. Can also contribute. Accordingly, it is preferable that the ultrafine bubbles permeate through the membrane pores. When the ultrafine bubbles are actually permeated through the membrane, the generation of bubbles may be confirmed on the membrane surface on the permeate side of the membrane.

  FIG. 1 is a schematic explanatory diagram (schematic flow diagram) showing an example of a water purification system (equipment) and a method for operating the water purification system of the present invention. The operation method of the water purification system (equipment) and the water purification system of the present invention is not limited to the one shown in FIG. 1, and if necessary, coagulation treatment with a coagulant, activated carbon treatment, other separation membrane treatment, etc. These known water purification means can be combined.

  Raw water (treated water) that has been sent and stored in the raw water tank 3 from the raw water supply line 1 through the pre-filter 2 is supplied from the raw water supply line 4 to the membrane module 11 by a water supply pump (raw water supply pump) 6. An air suction port (gas supply means; air supply port) 5 for introducing air into the raw water is provided on the upstream side of the water pump 6. On the downstream side (discharge side) of the water pump 6 is provided an ultrafine bubble generator 7 (which will be described in detail later). A plurality of raw water supply lines 4 may be provided, and one of them may be connected between the water feed pump 6 and the ultrafine bubble generator 7. The pre-filter 2 is attached for the purpose of removing raw water impurities. The prefilter 2 may be installed downstream from the raw water tank 3. The filtration accuracy (filtration opening) of the prefilter is desirably smaller than the gap or slit width to which high-speed shearing is applied in the ultrafine bubble generator, for example, 5-200 μm, preferably 10-150 μm, more preferably 50- 100 μm. The form of the prefilter is not particularly limited, but an auto strainer, a cartridge filter, a membrane filter, or the like can be used.

  In the ultrafine bubble generating device 7, a large number of ultrafine bubbles are generated in the raw water by the air supplied from the air suction port 5. The raw water containing ultrafine bubbles prepared by the ultrafine bubble generator 7 passes through valves 8 and 9 and is placed at the lower end of a membrane module (hollow fiber membrane module; internal pressure type cross-flow filtration method) 11 installed vertically. It is supplied to the membrane module 11 from the provided ultrafine bubble-containing raw water supply port 10. The raw water can be subjected to a coagulation treatment with a coagulant if necessary depending on the concentration of suspended solids (SS) in the raw water, the size of the suspended solids, and the like.

  The membrane module 11 is a housing in which a hollow fiber membrane bundle is accommodated in a housing, and has an ultrafine bubble-containing raw water supply port 10, a permeate discharge port 18, and a concentrate discharge port 12. It suffices that at least one ultrafine-bubble-containing raw water supply port and permeate take-out port are provided. In the case of total filtration, the concentrate discharge port 12 need not be provided. The raw water supply port 10 containing ultrafine bubbles is used as a back pressure cleaning drain port during back pressure cleaning. In the hollow fiber membrane bundle, both ends of a required number of hollow fiber membranes are integrated with an adhesive or the like, and both ends of the hollow fiber membrane are opened, and are fixed to the inner wall surface of the housing. Adjustment of the supply amount of raw water containing ultrafine bubbles is performed by a valve 8.

  In the membrane module 11, the permeated water that has been membrane-filtered under a predetermined condition is sent to the permeated water tank 21 through the permeated water line 20 through the valve 19 and stored therein. The concentrated liquid is circulated to the water supply pump 6 through the concentrated circulating water line 17 by adjusting the concentrated liquid circulation flow rate and the cross flow speed by operating the valve 14. A part or all of the concentrated liquid may be discarded through the drainage line 16. Reference numerals 15a and 15b denote valves. In the middle of the concentrated circulating water line 17, a concentrated circulating water pump, an ultrafine bubble generating device, and an air supply port may be provided to generate ultrafine bubbles in the concentrated circulating water and supply them to the membrane module 11.

  During the membrane filtration operation, it is desirable to periodically perform back pressure washing with water or air in order to maintain the filtration capacity. When water is used as the back pressure cleaning medium, the back pressure pump 22 is operated to press the permeated water in the permeated water tank 21 through the back pressure cleaning line 25 from the permeated water outlet 18 of the membrane module 11. The membrane (hollow fiber membrane) is back-pressure washed. The flow rate at the time of back pressure washing is preferably 1 to 5 times the filtration flow rate. Back pressure washing may be performed using an aqueous sodium hypochlorite solution. In that case, the sodium hypochlorite aqueous solution in the sodium hypochlorite aqueous solution tank 23 is supplied into the back pressure washing line 25 by the chemical pump 24.

  The membrane filtration operation using ultrafine bubbles may supply gas to the raw water continuously for a long period of time, but if necessary, a stop period for stopping the supply of gas may be provided periodically. Good. Even if gas is not actively supplied to the raw water, ultrafine bubbles may be generated by the gas dissolved in the raw water or a small amount of mixed gas. The gas supply stop period can be provided, for example, for about 0.1 to 5 days after the membrane filtration operation is performed for about 1 to 30 days.

  In the membrane filtration operation using ultrafine bubbles, a period for intermittently stopping the membrane filtration operation or a period for lowering the filtration flux (flux) may be provided periodically. By providing these, the effect of cleaning the membrane by the ultrafine bubbles is increased, and thus a stable filtration operation can be performed for a longer period of time. As a period for stopping the membrane filtration operation, for example, after the membrane filtration operation is performed for about 1 day to 30 days, it can be provided for about 0.1 day to 1 day.

  The ultrafine bubble generator 7 will be described in more detail below.

  FIG. 3 is a cross-sectional view showing an example of an ultrafine bubble generator. In this example, the ultrafine bubble generating device 7 includes a cylindrical casing 71 having a low height compared to its diameter, and two upper and lower disks 74 and 75 installed horizontally inside the casing 71. It consists of A gas-liquid mixed flow inlet 72 is provided at the lower portion of the casing 71, and a gas-liquid mixed flow outlet 73 is provided at the upper portion. The disc 74 located below the two discs is donut-shaped and is installed on the bottom surface inside the casing 71. The disc 75 located above the two discs has a disk shape with substantially the same diameter as the disc 74 and is installed so as to cover the disc 74. In the circumferential direction of the peripheral portions of the opposing surfaces of the disks 74 and 75, an annular slit is formed through which the gas-liquid mixture pressurized by the water pump 6 is passed and ejected outward. The jet direction of the gas-liquid mixture is a direction orthogonal to the inflow direction of the gas-liquid mixture flowing into the region partitioned by the disk 74 and the disk 75 from the gas-liquid mixture flow inlet. When the pressurized gas-liquid mixture passes through the annular slit, a large number of ultrafine bubbles are generated, and the gas-liquid mixture containing the ultrafine bubbles (ultrafine bubble mixture) flows out from the gas-liquid mixture flow outlet 73. And supplied to the membrane module 11. The arrows in FIG. 3 indicate the flow of the gas-liquid mixture. Since the gas-liquid mixture distribution outlet 73 is provided in the upper part of the housing 71, the gas does not stay and the ultrafine bubble mixture is smoothly supplied to the membrane module 6. Thus, in the present invention, it is preferable that the ultrafine bubble generator has a structure in which gas does not stay as much as possible.

  In the ultrafine bubble generator 7, for example, by adjusting the structure of the annular slit, the passage speed of the gas-liquid mixture in the annular slit, the supply ratio of gas and liquid, etc., the (ultra) fine bubbles in the ultrafine bubble mixture are adjusted. The bubble diameter, bubble diameter distribution, and number of bubbles can be controlled. The number of bubbles, bubble diameter, bubble diameter distribution, and the like can be measured using a particle counter as described above.

  It is preferable that the annular slit includes a flow path expanding portion 78 provided so as to expand from the gap minimum portion 77 from the inner diameter side toward the outer diameter side. When the annular slit has such a structure, the gas-liquid mixture passes through and ejects at a high speed, so that ultrafine bubbles are generated in the gas-liquid mixture due to a change in the gap between the channels. This is because the flow rate of the gas-liquid mixture changes when the gas-liquid mixture passes through the flow path (flow path expanding portion 78) continuously expanding from the gap minimum portion 77 from the inner diameter side toward the outer diameter side. This is because the pressure changes.

  The preferable structure of the annular slit is not particularly limited as long as it has the flow path expanding portion 78 provided so as to expand from the minimum gap portion 77 at least from the inner diameter side to the outer diameter side. On the inner diameter side of the portion 77, there may be provided a flow path reducing portion 76 in which the flow path is continuously reduced toward the smallest gap portion. In addition, the annular slit has a structure in which the channel cross-sectional area increases stepwise from the inner diameter side to the outer diameter side, a structure in which the channel cross-sectional area decreases stepwise from the inner diameter side to the outer diameter side, You may have the structure where a flow-path cross-sectional area increases continuously toward an outer diameter side, and the structure where a flow-path cross-sectional area decreases continuously from an inner diameter side toward an outer diameter side. In the present invention, from the viewpoint of efficiently generating ultrafine bubbles, it is preferable that the annular slit includes a flow channel expanding portion in which the flow channel cross-sectional area continuously increases from the smallest gap portion from the inner diameter side toward the outer diameter side. .

  When the expansion angle (expansion angle in the cross section) θ2 of the annular slit in the flow path expansion portion 78 is made smaller than the reduction angle (reduction angle in the cross section) θ1 in the flow path reduction portion 76 from the viewpoint of the generation efficiency of the ultrafine bubbles. However, θ2 may be equal to or greater than θ1.

  By using the ultrafine bubble generator 7 having the above structure, the number of bubbles having a bubble diameter of 2 to 50 μm (number measured by a particle counter) is, for example, 100 / mL or more at 20 to 30 ° C. The raw water containing ultrafine bubbles can be obtained (preferably 300 / mL or more, more preferably 1000 / mL or more, particularly 2000 / mL or more). Further, when the ultrafine bubble generating device 7 having the above structure is used, the number of bubbles having a bubble diameter of 2 to 5 μm (the number measured by a particle counter) is, for example, 100 / It is possible to obtain a mixture of ultrafine bubbles that is mL or more (preferably 300 / mL or more, more preferably 1000 / mL or more, particularly 2000 / mL or more).

  In the above example, the water pump and the ultrafine bubble generating device are used as separate devices and devices, but the water pump and the ultrafine bubble generating device, or the two devices and the air suction port are integrated. May be. Below, the apparatus with which the water pump and the ultrafine bubble generator were integrated is demonstrated. In addition, also when using the apparatus with which the water pump shown in the following FIGS. 4-8 and the ultrafine bubble generating apparatus were integrated, at 20-30 degreeC similarly to the above, for example, 100 pieces / mL or more (preferably Can obtain raw water containing ultrafine bubbles of 300 / mL or more, more preferably 1000 / mL or more, particularly 2000 / mL or more, and the number of bubbles having a bubble diameter of 2 to 5 μm (measured with a particle counter). The number of particles) is, for example, 100 / mL or more (preferably 300 / mL or more, more preferably 1000 / mL or more, particularly 2000 / mL or more) at 20 to 30 ° C. Can be obtained.

  FIG. 4 shows an example of an apparatus in which a water pump and an ultrafine bubble generator are integrated (hereinafter, sometimes referred to as “ultrafine bubble generator pump” or “superfine bubble generator built-in water pump”). It is sectional drawing (sectional drawing of a liquid feeding dispersion | distribution part). FIG. 5 is a partially enlarged view (cross-sectional view) of a storage chamber of a device in which the liquid feed pump and the ultrafine bubble generating device of FIG. 4 are integrated.

  This ultrafine bubble generating pump disperses the gas supplied in the liquid as ultrafine bubbles, and includes a canned motor and a liquid feed dispersion unit. In FIG. 4, the canned motor portion is omitted. Reference numeral 30 denotes a rotating shaft of the canned motor, and reference numeral 31 denotes a front bearing box (front bearing housing fixing portion).

  The housing 34 is fastened and fixed in a liquid-tight manner to the front bearing box 31 with bolts 42. The housing 34 and the front bearing box 31 define a storage chamber 35. The casing 34 is provided with a liquid supply port 39 and a liquid outflow port 38. The liquid supply port 39 is provided at an extended position of the rotating shaft 30 of the rotor of the canned motor, and the liquid outlet 38 is provided on a surface located in a direction intersecting the rotating shaft 30 of the housing 34. .

  An impeller (pump impeller) 43 is stored in the storage chamber 35. The impeller 43 is fastened by a bolt 44 to the tip of the rotating shaft 30 of the canned motor. As shown in FIG. 4, the impeller 43 is formed of a closed type centrifugal impeller, and includes a centrifugal blade 46 for feeding liquid on the surface of a disk constituting a part of the impeller main body within the impeller main body 45. It becomes the composition. A circulation blade 47 is provided on the back side of the impeller body 45. The circulation blade 47 has a larger diameter than the centrifugal blade 46.

  The impeller 43 is configured such that a gap is generated between the facing surface 32 of the impeller main body 45 of the front bearing box 31 and the impeller 43 in the storage chamber 35. The interior of the storage chamber 35 is divided into a liquid feeding space 36 and a circulation space 37 by the impeller main body 45. The liquid feeding space 36 conveys the fluid in the storage chamber 35 to the liquid outlet 38 side by the centrifugal blades 46 of the impeller 43, and the supplied liquid is supplied to the centrifugal blades 46 and the circulating blades of the impeller 43 in the circulation space 37. Due to the pressure difference generated by 47, the impeller body 45 circulates in the centrifugal direction and the centripetal direction.

  A dispersion portion 48 is provided in the gap between the facing surface 32 of the impeller main body 45 of the front bearing box 31 and the impeller 43. The dispersion part 48 is disposed in contact with the facing surface 32 of the front bearing box 31. As shown in FIG. 5, the dispersion unit 48 includes a dispersion unit body composed of two disks 49 and 50, and the space between the disks 49 and 50 is distributed over (almost) the entire circumference of the disks 49 and 50. A flow path 51 (annular slit) is formed.

  As shown in FIG. 5, taper portions are formed to face each other so that the two disks 49 and 50 face each other so as to expand from the inner diameter side toward the outer diameter side. The channel 51 is provided with a channel reducing portion 51a in which the gap of the channel 51 is reduced from the outer diameter side toward the inner diameter side. Further, a flow path enlargement part 51b is formed on the inner diameter side of the flow path reduction part 51a so that the gap of the flow path 51 expands from the outer diameter side toward the inner diameter side. A gap minimum portion 51c in which the gap of the flow path 51 is the smallest is provided between the portion 51b. Thus, it is also preferable that the annular slit is provided with a flow path expanding portion provided so as to expand from the minimum gap portion from the outer diameter side toward the inner diameter side.

  The gas supply flow path 40 provided as a pipe line penetrating the front bearing box 31 opens at a position close to the rotating shaft 30 in the circulation space 37.

  Next, the operation of the ultrafine bubble generating pump will be described with reference to FIGS.

  When the rotating shaft 30 of the canned motor rotates, the impeller 43 also rotates together to take in the liquid from the liquid supply port 39. As the impeller 43 rotates, the liquid is sent in the centrifugal direction from the rotating shaft, and a part flows out from the liquid outlet 38.

  A pressure distribution is generated in the storage chamber 35 by the rotation of the impeller 43. In the pressure distribution, the pressure increases as the distance from the rotary shaft 30 increases. As shown in FIG. 5, the region A2 far from the rotary shaft 30 has a higher pressure than the region A1 near the rotary shaft 30.

  The liquid that has not flowed out from the liquid outlet 38 moves to the circulation space 37 of the impeller 43. In the circulation space 37, air and liquid taken in from the gas supply channel 40 exist. Since the pressure in the circulation space 37 is higher than the pressure in the fluid region A3 in the vicinity of the rotating shaft 30, the fluid moves so as to approach the rotating shaft. At this time, the gas-liquid mixture sequentially passes through the flow path reducing section 51 a and the flow path expanding section 51 b provided in the dispersion flow path 51 of the dispersion section 48 and moves in a direction approaching the rotating shaft 30. When the gas-liquid mixture passes through the flow path enlargement part 51b via the flow path reduction part 51a, the flow rate of the gas-liquid mixture changes due to the change in the flow path gap, the pressure changes, the gas is refined, and the ultrafine Bubbles are generated. That is, after pressurization with the impeller 43 of the pump, ultrafine bubbles are generated.

  This gas refinement is mainly determined by the flow rate of the liquid, the amount of gas, the gap size of the gap minimum portion 51c and the flow path enlargement portion 51b, and the like. For example, if the gas flow rate is below a certain threshold value, the bubble diameter is not reduced and sufficient miniaturization is not performed. In this case, the diameter of the bubbles to be refined can be adjusted mainly by the gap size of the gap minimum portion 51c and the flow path expanding portion 51b. On the other hand, when the flow rate of the liquid is equal to or higher than the threshold value, the bubble diameter is reduced and sufficient miniaturization is performed. The flow path enlargement part 51b provided in the dispersion flow path 51 exhibits the same effect as the Venturi tube, and the liquid accompanying the gas passes through the flow path 51 of the dispersion part 48, so that the gas can be refined. it can. The expansion angle (expansion angle in the cross section) of the dispersion flow path (annular slit) 51 in the flow path expansion section 51b is the reduction angle (reduction angle in the cross section) of the flow path contraction section 51a from the viewpoint of the ultrafine bubble generation efficiency. Although often smaller, the spread angle may be the same as or greater than the shrink angle.

  The circulation blade 47 provided on the back side of the impeller main body 45 generates a radiant flow, and moves the gas-liquid dispersion fluid in the circulation space 37 from the rotating shaft 30 side in the centrifugal direction. As described above, in the vicinity of the rotation axis in the circulation space 37, there is a gas-liquid dispersion fluid that has been refined by passing through the dispersion portion 48. Therefore, this fluid moves in the centrifugal direction from the rotation axis 30 side. .

  Further, the rotation of the circulation blade 47 increases the pressure of the fluid in the region A3 near the rotation shaft 30 and the outer region A4 of the circulation blade 47, so that the fluid in the circulation space 37 of the impeller body 45 is in the centrifugal direction and centripetal. Circulate and flow in the direction. In addition, due to the formation of a centrifugal pressure field by the rotation of the circulation blade, the outlet of the gas supply flow path 40 has a negative pressure and air self-priming is promoted.

  In the present embodiment, in order to promote the circulation of the fluid in the circulation space 37, the disk 50 provided on the side close to the impeller of the dispersion part 48 is provided with a partition part 50a extending to the rotating shaft side. Yes. By partitioning the inside of the circulation space 37 by the disk 50 (37a, 37b), in the space between the disk 50 including the partition part 50a and the surface facing the main body of the impeller, that is, the dispersion channel 51, the fluid flows in the centripetal direction. In addition, the fluid easily moves in the centrifugal direction in the space between the impeller body 45 and the disk 50 where the circulation blade 47 is located. By adopting such a configuration, circulation of the fluid in the circulation space 37 is promoted, and the fluid passes through the dispersion portion 48 more efficiently, so that the generation of ultrafine bubbles can be promoted. it can.

  The ultrafine bubble generating pump according to the present embodiment has a mechanism in which a part of the fluid pressurized by the centrifugal blade 46 in the storage chamber 35 causes a circulation flow behind the centrifugal blade 46. Further, air can be self-primed into the circulation flow path, and the self-supplied air can be merged with the flow of the centrifugal blade 46 and can be discharged from the liquid outlet 38. In addition, since the dispersion part is provided in the middle of the circulation flow and the bubbles can be made finer, the liquid can be transported and the fine bubbles can be generated with one apparatus. In addition, by providing the circulation vane 47 in the storage chamber 35, even when used under a pressurized condition, a differential pressure can be generated, and bubbles can be made finer.

  In the above example, the circulation blade 47 is provided outside the region partitioned by the two disks 49 and 50, but the circulation blade 47 is provided inside the region partitioned by the two disks 49 and 50. In addition, a flow path into which a fluid flows can be provided in a region defined by the two disks 49 and 50. In such an embodiment, contrary to the above example, the fluid (fluid pressurized by the impeller 43 of the pump) that flows into the region defined by the two disks 49 and 50 is dispersed in the dispersion channel (annular slit). ) In the order of the channel reducing portion, the gap minimum portion, and the channel expanding portion, and is ejected to the outside of the region (in the centrifugal direction) to generate ultrafine bubbles.

  In the above example, the dispersion portion 48 is provided in the vicinity of the impeller 43. However, after being pressurized by the impeller 43, ultrafine bubbles are generated in the gas-liquid mixture (for example, passing through an annular slit). As long as it has a mechanism, the dispersion part 48 may be provided at a position separated from the impeller 43.

  FIG. 6 is a cross-sectional view showing another example of a device in which a water pump and an ultrafine bubble generator used in the method of the present invention are integrated (ultrafine bubble generator pump; water pump with a built-in ultrafine bubble generator). is there. FIG. 7 is a partially enlarged view (cross-sectional view) of a pump part and a dispersion part (ultrafine bubble generation part) of the water pump with a built-in ultrafine bubble generation apparatus of FIG. 6 and 7, arrows indicate the flow direction of the liquid and gas-liquid mixture. In FIG. 6, “MB generation part” means a dispersion part (ultrafine bubble generation part).

  This ultrafine bubble generating pump disperses the gas supplied in the liquid as ultrafine bubbles, and includes a motor part (canned motor part), a pump part, and an ultrafine bubble generating part. Reference numeral 230 denotes a rotating shaft of the canned motor.

  The pump unit is provided with a liquid supply port 239, a gas supply channel 240, and an air vent valve 260. The liquid supply port 239 is provided at an extension position of the rotating shaft 230 of the rotor of the canned motor, and the air vent valve 260 is provided on a surface located in a direction intersecting the rotating shaft 230. Reference numeral 259 denotes a valve.

  An impeller (pump impeller) 243 is accommodated in the pump unit. The impeller 243 is attached to the tip of the rotating shaft 230 of the canned motor. As shown in FIGS. 6 and 7, the impeller 243 is formed of a closed type centrifugal impeller, and a centrifugal blade 246 for feeding a liquid to the surface of a disk constituting a part of the impeller main body inside the impeller main body. It is the composition provided with. Due to the high speed rotation of the impeller 243, the vicinity of the liquid supply port 239 becomes negative pressure, and air is sucked from the gas supply channel 240.

  The liquid and gas (air) that flowed into the pump unit from the liquid supply port 239 and the gas supply channel 240 are mixed by the centrifugal blade 246 and moved in the centrifugal direction, and then ultrafine provided between the pump unit and the motor unit. It flows into the bubble generator. As shown in FIG. 7, the ultrafine bubble generating portion includes a dispersion portion main body constituted by two disks 249 and 250, and between these disks 249 and 250, the peripheral edges of the disks 249 and 250 are arranged. Dispersion flow paths 251 (annular slits) are formed over (almost) the entire circumference. In addition, in a region defined by two disks 249 and 250, a rotating body 252 is provided on the rotating shaft 230, and the rotating body 252 is configured by a disk 252a and a plurality of centrifugal blades 252b.

  As shown in FIG. 7, taper portions are formed to face each other on the facing surfaces of the two disks 249 and 250 so as to expand from the inner diameter side toward the outer diameter side. The channel 251 is provided with a channel reducing portion 251a in which the gap of the channel 251 is reduced from the inner diameter side toward the outer diameter side. Further, a flow path enlargement part 251b is formed on the outer diameter side of the flow path reduction part 251a, and the gap of the flow path 251 expands from the inner diameter side toward the outer diameter side. A gap minimum portion 251c where the gap of the flow path 251 is the smallest is provided between the enlarged portion 251b.

  Next, the operation of the ultrafine bubble generating pump will be described with reference to FIGS.

  When the rotating shaft 230 of the canned motor rotates, the impeller 243 also rotates integrally to take in liquid from the liquid supply port 239 and gas (air) from the gas supply flow path 240. As the impeller 243 rotates, the gas-liquid mixture is sent in the centrifugal direction from the rotating shaft, and further moves to the ultrafine bubble generating unit.

  In the ultrafine bubble generating unit, the gas-liquid mixture flows into the region defined by the two disks 249 and 250 by the high-speed rotation of the rotating shaft 230, and the dispersing unit 248 by the rotation of the centrifugal blade 252 b of the rotating body 252. The flow path reducing section 251a and the flow path expanding section 251b provided in the dispersion flow path 251 are sequentially passed. When the gas-liquid mixture passes through the flow path reduction section 251a and the flow path expansion section 251b, the flow rate of the gas-liquid mixture changes due to the change in the flow gap, the pressure changes, the gas is refined, and the ultrafine Bubbles are generated. That is, after pressurization with the impeller 243 of the pump, ultrafine bubbles are generated.

  As described above, this gas refinement is mainly determined by the flow rate of the liquid, the amount of gas, the gap size of the gap minimum portion 251c and the flow path enlargement portion 251b, and the like. The expansion angle (expansion angle in the cross section) of the dispersion flow path (annular slit) 251 in the flow path expansion section 251b is the reduction angle (reduction angle in the cross section) of the flow path reduction section 251a from the viewpoint of the generation efficiency of ultrafine bubbles. Although often smaller, the spread angle may be the same as or greater than the shrink angle.

  FIG. 8 is a cross-sectional view showing still another example of a device in which a water pump and an ultrafine bubble generator used in the method of the present invention are integrated (superfine bubble generator pump; water pump with a built-in ultrafine bubble generator). It is. In FIG. 8, the arrows indicate the flow direction of the liquid and gas-liquid mixture. Further, “MB generation part” means a dispersion part (ultrafine bubble generation part).

  This ultrafine bubble generating pump disperses the gas supplied in the liquid as ultrafine bubbles, and includes a motor part (canned motor part), a pump part, and an ultrafine bubble generating part. Reference numeral 330 denotes a rotating shaft of the canned motor. The pump part and the ultrafine bubble generating part are provided on both sides of the motor part.

  A liquid supply port 339 and a gas supply channel 340 are provided in the pump unit. The liquid supply port 339 is provided at the extended position of the rotating shaft 330 of the rotor of the canned motor. Reference numeral 359 denotes a valve.

  An impeller (pump impeller) 343 is accommodated in the pump unit. The impeller 343 is attached to the tip of the rotating shaft 330 of the canned motor. As shown in FIG. 8, the impeller 343 includes a closed type centrifugal impeller, and the impeller main body includes a centrifugal blade 346 for feeding liquid on the surface of a disk constituting a part of the impeller main body. It has a configuration. Due to the high speed rotation of the impeller 343, the vicinity of the liquid supply port 339 becomes negative pressure, and air is sucked from the gas supply flow path 340.

  The liquid and gas (air) that flowed into the pump unit from the liquid supply port 339 and the gas supply flow path 340 are mixed by the centrifugal blade 346, and a part thereof is used for cooling the canned motor (after circulating through the cooling line, After returning to the pump part), the rest moves in the centrifugal direction, and then flows into the ultrafine bubble generating part through the intermediate pipe 370. As shown in FIG. 8, the ultrafine bubble generating portion includes a dispersion portion main body constituted by two discs 349 and 350, and between these discs 349 and 350, the discs 349 and 350 have a peripheral portion. A dispersion channel 351 (annular slit) is formed over (almost) the entire circumference. Further, in a region partitioned by two disks 349 and 350, a rotating body 352 is provided on the rotating shaft 330, and the rotating body 352 is constituted by a disk 352a and a plurality of centrifugal blades 352b.

  As shown in FIG. 8, tapered portions are formed so as to face each other so as to expand from the inner diameter side toward the outer diameter side on the facing surface on the side where the two disks 349 and 350 face each other. The channel 351 is provided with a channel reducing portion 351a in which the gap of the channel 351 is reduced from the inner diameter side toward the outer diameter side. Further, a flow path expanding portion 351b is formed on the outer diameter side of the flow path reducing portion 351a, and the gap of the flow path 351 expands from the inner diameter side toward the outer diameter side. A minimum gap portion 351c in which the gap of the flow path 351 is the smallest is provided between the enlarged portion 351b. Note that an air bleeding valve 360 is provided on a surface located in a direction intersecting the rotating shaft 330 in the ultrafine bubble generating unit.

  Next, the operation of the ultrafine bubble generating pump will be described with reference to FIG.

  When the rotating shaft 330 of the canned motor rotates, the impeller 343 also rotates integrally, and takes in liquid from the liquid supply port 339 and gas (air) from the gas supply flow path 340. As the impeller 343 rotates, the gas-liquid mixture is sent in the centrifugal direction from the rotating shaft, and moves to the MB generating section through the intermediate pipe 370.

  In the MB generator, the gas-liquid mixture flows into the region defined by the two disks 349 and 350 due to the high-speed rotation of the rotating shaft 330, and the dispersion of the dispersion part 348 is caused by the rotation of the centrifugal blade 352 b of the rotating body 352. It passes through the flow path reduction part 351a and the flow path enlargement part 351b provided in the flow path 351 in order. Then, when the gas-liquid mixture passes through the flow path reduction section 351a and the flow path expansion section 351b, the flow rate of the gas-liquid mixture changes due to the change in the flow path gap, the pressure changes, the gas is refined, and the ultrafine Bubbles are generated. That is, after pressurization with the impeller 343 of the pump, ultrafine bubbles are generated.

  As described above, this gas refinement is mainly determined by the flow rate of the liquid, the amount of gas, the gap size of the gap minimum portion 351c and the flow path expanding portion 351b, and the like. The expansion angle (expansion angle in the cross section) of the dispersion flow path (annular slit) 351 in the flow path expansion section 351b is the reduction angle (reduction angle in the cross section) of the flow path contraction section 351a in terms of the efficiency of generating ultrafine bubbles. Smaller is preferred.

  FIG. 2 is a schematic explanatory diagram (schematic flow diagram) showing another example of the operation method of the water purification system of the present invention. In the figure, 108 is a valve, 109 is a flow rate adjusting valve, 128 is a pressure gauge, and 129 is a flow meter.

  The raw water (treated water) stored and fed from the raw water supply line 101 to the raw water tank 103 is converted into a membrane by an ultrafine bubble generating pump (an apparatus in which the water supply pump and the ultrafine bubble generating device are integrated) 106 from the raw water supply line 104. It is supplied to a module (filter) 111. The ultrafine bubble generating pump 106 is provided with an air suction port (gas supply means; air supply port) 105 for introducing air into the raw water. The air suction port 105 may be provided either before or after pressurization by the pump impeller, but is preferably provided before pressurization by the pump impeller from the viewpoint that it can be self-sucked. A plurality of raw water supply lines 104 may be provided. A prefilter may be attached at an appropriate position for the purpose of removing impurities in the raw water. As the ultrafine bubble generating pump 106, for example, the one described above can be used.

  A large number of ultrafine bubbles are generated in the raw water by the ultrafine bubble generation pump 106. The ultrafine bubble-containing raw water prepared by the ultrafine bubble generation pump 106 passes through the valve V-4 and the flow rate adjustment valve FCV, and is supplied to the side of the membrane module (filter) 111 installed vertically. It is supplied to the membrane module (filter) 111 from the raw water supply port 110 containing fine bubbles.

  The membrane module (filter) 111 includes a cylindrical filtration filter 126 housed in a cylindrical housing. The membrane module (filter) 111 includes an ultrafine bubble-containing raw water supply port 110, a filtered water discharge port 118, and a concentrate drainage port 112. Have. It is sufficient that at least one ultrafine bubble-containing raw water supply port and filtered water take-out port are provided. The filter 126 contains an element such as a cylindrical element made of sintered wire mesh.

  In the membrane module (filter) 111, the filtered water that has been membrane filtered under a predetermined condition is recovered from the filtered water and the concentrated liquid drain line 116 via the filtered water outlet 118 and the valve V-6.

  During the membrane filtration operation, it is desirable to periodically perform back-pressure washing in order to maintain the filtration capacity. In the reverse pressure cleaning, for example, in the state of the membrane filtration operation, the pressure inside the filtration filter is increased by closing the valve V-6, and after completion of the pressure increase, the valve V-4 is closed and the filtration filter 126 is in the pressurized state. After sealing, the valves V-7 and V-8 are opened at once, the pressure inside the filter is depressurized toward the primary side (concentrate drainage side), the element is washed, and the washing solution (including the concentrate) is concentrated. The liquid is discharged from the liquid drain port 112 through the concentrated liquid drain line 113, through the valve V-8, and through the filtered water and the concentrated liquid drain line 116. In this way, by regularly performing back-pressure washing in the membrane filtration operation, the filtration operation can be continued for a long period of time while suppressing clogging of the filter element.

  When the membrane filtration operation is performed for a long period of time, turbidity accumulates inside the filter, and thus it is necessary to periodically discharge such turbidity. In that case, the filtered water is periodically stored in the filtrate water tank 121 through the filtrate water line 120 from the valve V-9 side, and then the valves V-1 and V-2 are switched, and the valves V-7 and V- 8 is opened, and the filtered water is sent to the filtration filter 126 using the ultrafine bubble generation pump 106, thereby renewing the water on the primary side (concentrated liquid side) inside the filter, Prevent excessive turbidity increase in raw water. As for the route for sending the filtrate to the filtration filter 126, a flushing method for feeding from the V-4 side and a backflow method for feeding from the V-5 side can be used properly.

  FIG. 11 is a schematic explanatory diagram (schematic flowchart) showing still another example of the operation method of the water purification system of the present invention. In the figure, 108 is a valve, 109 is a flow rate adjusting valve, 128 is a pressure gauge, and 129 is a flow meter.

In this example, the above-described clean water and / or permeated water (filtered water) from the membrane module is pressurized by a water supply pump, and after the pressurization by the water supply pump and before the membrane module is supplied, In addition to generating ultrafine bubbles in the permeated water (filtered water) from the membrane module, the ultrafine bubble-containing liquid obtained in this way is used for cleaning the device or apparatus to be cleaned, and the obtained cleaning liquid after use is used. It is an example of the aspect which supplies to a membrane module, performs membrane filtration, and purifies water.

  The filtrate stored in the filtrate tank 121 from the membrane module (filter) 111 via the valves V-6 and V-9 and through the filtrate water line 120 passes through the valve V-10 and is ultrafine from the filtrate circulation line 117. Supplyed from a valve V-3 through a tank supply liquid line 132 to a tank 130 with a stirrer 131, which is a device to be cleaned or a device, by a bubble generation pump (a device in which a water pump and an ultrafine bubble generation device are integrated) 106. Is done. The ultrafine bubble generating pump 106 is provided with an air suction port (gas supply means; air supply port) 105 for introducing air into the raw water. The air suction port 105 may be provided either before or after pressurization by the pump impeller, but is preferably provided before pressurization by the pump impeller from the viewpoint that it can be self-sucked. As the ultrafine bubble generating pump 106, for example, the one described above can be used.

  A large number of ultrafine bubbles are generated in the raw water by the ultrafine bubble generation pump 106. For this reason, the cleaning liquid supplied to the tank 130 includes ultrafine bubbles having a very small bubble diameter, and an excellent cleaning effect is exhibited even against contamination of fine portions of the tank 130. In addition, a part or all of the filtered water can be replaced with clean water.

  The liquid after washing the tank contains ultrafine bubbles provided on the side of the membrane module (filter) 111 installed vertically through the membrane module supply liquid line 133 through the valve V-4 and the flow rate adjustment valve FCV. It is supplied to the membrane module (filter) 111 from the raw water supply port 110.

  The membrane module (filter) 111 includes a cylindrical filtration filter 126 housed in a cylindrical housing. The membrane module (filter) 111 includes an ultrafine bubble-containing raw water supply port 110, a filtered water discharge port 118, and a concentrate drainage port 112. Have. It is sufficient that at least one ultrafine bubble-containing raw water supply port and filtered water take-out port are provided. The filter 126 contains an element such as a cylindrical element made of sintered wire mesh.

  In the membrane module (filter) 111, the filtered water membrane-filtered under a predetermined condition is stored in the filtered water tank 121 through the filtered water line 120 through the filtered water outlet 118 and valves V-6 and V-9. The

  During the membrane filtration operation, it is desirable to periodically perform back-pressure washing in order to maintain the filtration capacity. In the reverse pressure cleaning, for example, in the state of the membrane filtration operation, the pressure inside the filtration filter is increased by closing the valve V-6, and after completion of the pressure increase, the valve V-4 is closed and the filtration filter 126 is in the pressurized state. After sealing, the valves V-7 and V-8 are opened at once, the pressure inside the filter is depressurized toward the primary side (concentrate drainage side), the element is washed, and the washing solution (including the concentrate) is concentrated. The liquid is discharged from the liquid drain port 112 through the concentrated liquid drain line 113, through the valve V-8, and through the filtered water and the concentrated liquid drain line 116. When a sudden pressure drop inside the filter occurs, the ultrafine bubbles present in the liquid infiltrated inside the filtration device (especially the deposits accumulated in the filter element and separation membrane of the filter) expand and accumulate. Things break up. In addition, since a pressure drop occurs from the stock solution side (primary side), the pressure on the filtrate side (secondary side) also escapes to the primary side, so a back flow of the filtrate occurs, and the crushed sediment is filtered. Alternatively, they are separated along the flow from the separation membrane surface. For this reason, deposits on the film surface (dirt on the tank, etc.) are efficiently and reliably peeled off from the film surface.

  According to the above method, since the tank is washed with the cleaning liquid containing the ultrafine bubbles, it is possible to clean the entire tank by the action of the ultrafine bubbles. Moreover, the liquid after cleaning (used cleaning liquid) is purified by a filtration filter, and the purified filtered water is also reused as a cleaning liquid. Furthermore, since filtered water is used, the pump is not blocked. Further, in the above-described back pressure cleaning, clogging of the filtration filter can be effectively prevented by the action of ultrafine bubbles. For this reason, it is possible to clean a device such as a tank or a device very efficiently.

  In addition, the operating method of the water purification system of this invention is applicable also to the pre-processing of the membrane module before use. That is, in the operation method of the water purification system, purified water such as permeated water is supplied to the membrane module by the water supply pump instead of the raw water, and after the pressurization by the water supply pump, ultrafine bubbles are generated. By filtering the clean water under pressure, the contact angle of the membrane surface is changed (hydrophilized), and a membrane module that is not easily contaminated can be obtained.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples.

Example 1
The membrane filtration operation was performed by the water purification system (equipment) shown in FIG. Raw water (Ribo River water) was fed through the raw water supply line 1 to the raw water tank 3 via the pre-filter 2 (auto strainer). As the prefilter 2, a product name “Juraclean” (filtration accuracy: 100 μm) manufactured by Central Filter Industry Co., Ltd. was used. A hollow fiber membrane module 11 [UF membrane, which is installed vertically while generating ultrafine bubbles from the raw water in the raw water tank 3 through the raw water supply line 4 and using the water pump 6 on the downstream side of the water pump 6. Molecular weight cut-off: 150,000 (pore diameter 0.01 μm), membrane material: cellulose acetate, membrane shape: internal pressure type hollow system, membrane inner diameter: 0.8 mm, membrane outer diameter: 1.3 mm, effective membrane area: 5 m ² , module outer shape Dimensions: 1126 mm, pure water permeation performance: 3000 L / hr · 0.1 MPa · 25 ° C.]. In the middle of the line, air is mixed into the raw water at a flow rate of 0.13 L / min0 (standard state) from the air suction port 5 provided on the upstream side of the water pump 6, and the raw water mixed with air is mixed by the water pump 6. It supplied to the ultrafine bubble generator 7 provided in the downstream of the water pump 6, and the ultrafine bubble containing raw water was prepared with the ultrafine bubble generator 7. FIG. The pressure (filtration pressure) on the discharge side of the water pump 6 was 0.05 MPa (gauge pressure), and the pressure on the suction side of the water pump 6 was -0.01 MPa (gauge pressure). The filtration method is an internal pressure type cross flow method (cross flow speed: 0.05 m / s).

  As shown in FIG. 3, the ultrafine bubble generating device 7 includes a cylindrical casing 71 provided with a gas-liquid mixture distribution outlet 73 and a gas-liquid mixture distribution inlet 72 on the upper and lower sides, and the interior of the casing 71. The upper and lower disks 74 and 75 are installed horizontally, and are provided in the circumferential direction on the peripheral surfaces of the opposing surfaces of the two disks, and let the gas-liquid mixture inside the housing 71 pass through and be ejected. Thus, an apparatus in which an annular slit for generating ultrafine bubbles was formed in the gas-liquid mixture was used.

  The dimensions of each part are as follows. Diameter of housing 71: 208.3 mmφ, diameter of disk 75: 198 mmφ, gap of gap slit minimum portion 77: 0.2 mm, diameter of gas / liquid mixture inlet 72 and gas / liquid mixture outlet 73: 38 .6 mmφ, an expansion angle (expansion angle in the cross section) θ2: 5 ° in the annular slit flow passage enlargement portion 78, and a reduction angle (reduction angle in the cross section) θ1: 90 ° in the annular slit flow passage reduction portion 76. .

The permeated water filtered through the pressure membrane in the hollow fiber membrane module 11 was sent to the permeated water tank 21 through the permeated water line 20 and stored. The concentrated liquid was drained through the line 16 until 23 days from the start of operation, and thereafter circulated to the water pump 6 through the concentrated circulating water line 17. At this time, backwashing was performed for 30 seconds every other hour using an aqueous sodium hypochlorite solution adjusted to an effective chlorine concentration of 3 to 5 ppm by injecting sodium hypochlorite into the permeated water. After 23 days, the membrane filtration operation was carried out for 23 to 51 days by switching to a line for circulating the entire concentrate. Changes in actual flux were measured and shown in FIG. 9 as changes over time in 20 ° C. equivalent flux [m / day]. In addition, it operated on the conditions of 2.0-2.5 m / day of flux until 7th after the operation start. The air supply from the air suction port 5 was stopped and the air flow rate was slightly unstable between 14 and 23 days and 38 and 51 days after the start of operation. In either case, a constant amount of air was not supplied, but although the flux decreased slightly, there was no rapid decrease. When 51 days have passed, the ultrafine bubble generating device 7 was removed and replaced with a short pipe (ordinary piping), and the membrane filtration operation was performed under the conditions where no ultrafine bubbles were generated for 51 to 60 days. The operation was stopped from 60 to 71 days, and from 71 days, the short tube was replaced with the ultrafine bubble generator 7 again, and the operation was continued.
As a result, when the ultrafine bubble generator was operated, a high level of flux of 2.5 to 3.0 m / day could be maintained. When the ultrafine bubble generator was replaced with a short tube, the flux decreased rapidly.

  When the number of microbubbles generated when the ultrafine bubble generator 7 was in operation (at the time of air supply) was measured with a particle counter, the number of bubbles with a bubble diameter of 2 to 50 μm was 2000 / mL or more.

Example 2
Membrane filtration operation was performed by the water purification system (equipment) shown in FIG. As the filter 126, a cylindrical element made of SUS special sintered wire mesh (manufactured by Central Filter Industrial Co., Ltd., trade name “PM-A-C65 * 40 * 250-GL”, filter medium size Φ65 / Φ40 × 250L, filtration area 0.05 m ² ) filled in a cylindrical housing was used. As the ultrafine bubble generating pump 106, the pump shown in FIG. Moreover, as raw water, water added with 100 ppm by weight of kaolin for biochemistry (manufactured by Wako Pure Chemical Industries, Ltd.) (pseudo sludge) was used.
(1) The raw water containing ultrafine bubbles by the ultrafine bubble generation pump 106 is filtered from the valve V-4 side with a special element in the filtration filter, and filtered water is obtained from the valve V-6 (valve V- 2, V-5, V-7, and V-8 are closed) [filtration operation].
(2) The pressure inside the filtration filter is increased by closing the valve V-6 in the state of the filtration operation [pressure process].
(3) After completion of pressurization, valve V-4 is closed and the filter is sealed in a pressurized state, then valves V-7 and V-8 are opened at once, and the pressure inside the filter is changed to the primary side (concentrate drainage). Side) direction and perform special element cleaning [depressurization process-return].
The membrane filtration operation was performed by repeating the operations (1) to (3). One cycle of the above operations (1) to (3) was set to 3 minutes. For comparison, a membrane filtration operation was performed in the same manner except that air was not supplied from the air suction port 105 to the ultrafine bubble generation pump 106 (an example in which raw water not containing ultrafine bubbles was supplied to the filtration filter). .
FIG. 10 shows a graph showing the relationship between the filtration flow rate and the elapsed time for each of the case where the ultrafine bubbles were added and the case where the ultrafine bubbles were not added. In FIG. 10, “with bubbles” refers to the case where ultrafine bubbles are added, and “without bubbles” refers to the case where no ultrafine bubbles are added.
The measured value of the filtration flow rate is a value obtained by reading the flow rate immediately after the restart of operation after the depressurization step performed at the end of each cycle with an area flow meter.
As seen in FIG. 10, the flow rate drop at the initial stage of operation occurred in any operation, but the subsequent reduction of the filtration flow rate was performed using raw water without adding ultrafine bubbles when using ultrafine bubble added raw water. Compared with the case where it was, the operation was light and stable. In the elapsed time range shown in FIG. 10, when the flow rate reduction portion generated immediately after the start was removed, the reduction rate of the filtration flow rate when using the ultrafine bubble added raw water was about 10%. On the other hand, the rate of decrease in the filtration flow rate when using raw water without adding ultrafine bubbles was about 35%.

1,101 Raw water supply line 2 Pre-filter 3,103 Raw water tank 4,104 Raw water supply line 5,105 Air suction port 6 Water supply pump (water supply pump)
7 Ultra Fine Bubble Generator 8, 108 Valve 9 Valve 10, 110 Ultra Fine Bubble Containing Raw Water Supply Port 11 Membrane Module 12, 112 Concentrate Discharge Port 13 Back Pressure Washing Drain Line 14 Valve 15a, 15b Valve 16 Drain Line 17 Concentration Circulation Water line 18 Permeated water outlet 19 Valve 20 Permeated water line 21 Permeated water tank 22 Backwash pump 23 Sodium hypochlorite aqueous solution tank 24 Chemical liquid pump 25 Back pressure washing line 106 Ultra fine bubble generating pump 109 Flow rate adjusting valve 111 Membrane Module (filter)
113 Condensate drain line 116 Filtrate and concentrate drain line 117 Filtrate circulation line 118 Filtrate outlet 120 Filtrate line 121 Filtrate tank 126 Filtration filter 127 Raw water return line 128 Pressure gauge 129 Flow meter 130 Tank 131 Stirrer 132 Tank Supply liquid line 133 Membrane module supply liquid line 30, 230, 330 Rotating shaft of canned motor 31 Front bearing box 32 Opposing surface of impeller main body 45 of front bearing box 33 Lubricating liquid outlet 34 Housing 35 Storage chamber 36 Feed Liquid space 37 Circulating space 38, 238, 338 Liquid outlet 39, 239, 339 Liquid supply port 40, 240, 340 Gas supply passage 41 Lubricating liquid conduit 42 Bolt 43, 243, 343 Impeller 44 Bolt 45 Impeller body 46 , 246, 346 far Core blade 47 Circulating blade 48, 248, 348 Dispersion part 49, 249, 349 Disc 50, 250, 350 Disc 50a Partition part 51, 251, 351 Dispersion flow path 51a, 251a, 351a Flow path reduction part 51b, 251b, 351b Flow Road expansion portion 51c, 251c, 351c Minimum gap portion 259, 359 Valve 260, 360 Air vent valve 370 Intermediate piping 71 Case 72 Gas-liquid mixed flow inlet 73 Gas-liquid mixed flow outlet 74 Disk 75 Disk 76 Flow path reducing portion 77 Gap Minimum part 78 Channel expansion part

Claims (14)

  In a water purification system using a membrane module, an operation method of a water purification system in which water is pressurized by a water supply pump and supplied to the membrane module to perform membrane filtration, after being pressurized by the water supply pump. An operation method of a water purification system, wherein ultrafine bubbles are generated in water before supplying a membrane module, and a liquid containing the ultrafine bubbles is supplied to the membrane module.   The operation method of the water purification system according to claim 1, wherein the water supplied to the water supply pump is raw water and / or concentrated circulating water from a membrane module.   The water to be supplied to the water supply pump is clean water and / or permeated water from the membrane module, and a liquid containing ultrafine bubbles is used for cleaning the apparatus or device to be cleaned, and then the cleaning liquid after use. The operation method of the water purification system according to claim 1, wherein the water is supplied to the membrane module.   The gas-liquid mixed fluid formed by mixing a gas-liquid mixed fluid obtained by mixing a gas with water through a flow path having a reduced portion, a most sandwiched portion, and an enlarged portion by high pressure from a water supply pump. The operation method of the water purification system according to any one of claims 1 to 3, wherein ultra fine bubbles mainly having a size of 50 µm or less are generated by changing a flow velocity and a pressure of a high-speed shear flow of fluid.   The operation of the water purification system according to any one of claims 1 to 4, wherein a filtration pressure when performing membrane filtration with a membrane module by pressurizing water with a water supply pump is 0.01 MPa (gauge pressure) or more. Method.   The operation method of the water purification system according to any one of claims 1 to 5, wherein the membrane filtration method in the membrane module is a cross flow filtration method.   The operation method of the water purification system according to any one of claims 1 to 6, wherein the membrane module is an ultrafiltration membrane module or a microfiltration membrane module.   The operation method of the water purification system according to any one of claims 1 to 7, wherein the membrane module is subjected to intermittent backwashing with permeated water from the membrane module or clean water supplied separately.   In a water purification system using a membrane module, a water supply pump for supplying water to the membrane module, a gas supply means for supplying gas into the water supply line, and a gas-liquid mixed fluid obtained by mixing gas in the water The flow rate and pressure of the high-speed shear flow of the gas-liquid mixed fluid formed in the flow path are changed by circulating the flow path having the reduced part, the most sandwiched part, and the enlarged part by high pressure by the water supply pump. A water purification system comprising ultrafine bubble generating means for generating ultrafine bubbles in water.   The water purification system according to claim 9, wherein the water supplied to the water supply pump is raw water and / or concentrated circulating water from a membrane module.   The water to be supplied to the water supply pump is clean water and / or permeated water from the membrane module, and includes a device to be cleaned or a device to be cleaned with a liquid containing ultrafine bubbles therein. The water purification system according to claim 9, wherein the liquid after cleaning of the apparatus is supplied to the membrane module.   The water purification system according to any one of claims 9 to 11, wherein the gas supply means is provided immediately before the water supply pump.   Furthermore, the water purification system of any one of Claims 9-12 provided with the washing | cleaning means which backwashes a membrane module intermittently.   Furthermore, the water purification system of any one of Claim 10 with which the pre filter which removes the contaminant of raw | natural water is provided.

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