JP2013163141A - Membrane filtration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve cleaning efficiency of a pretreatment membrane used with a reverse osmosis membrane.SOLUTION: A membrane filtration system includes: a pretreatment membrane; a high-pressure pump; a reverse osmosis membrane; and a fine bubble generator. The pretreatment membrane removes an insoluble component contained in water to be treated. The high-pressure pump applies pressure to the water to be treated from which the insoluble component is removed by the pretreatment membrane. The reverse osmosis membrane separates the water to be treated to which the pressure is applied into treatment water from which a soluble component containing the water to be treated is removed and concentrated water in which the soluble component is concentrated. The fine bubble generator generates fine bubbles by introducing the concentrated water discharged from the reverse osmosis membrane at high pressure and supplies the pretreatment membrane during cleaning with the concentrated water containing the fine bubbles.

Description

  The present invention relates to a membrane filtration system for treating water to be treated pretreated with a pretreatment membrane with a reverse osmosis membrane.

  In a membrane filtration system that produces domestic water, industrial water, agricultural water, or the like from seawater, brackish water, or groundwater containing ions and salts, a method that uses a reverse osmosis (RO) membrane may be used. The RO membrane has the property of allowing water to pass through but not allowing impurities other than water such as ions and salts to pass through. In this RO membrane, water and solute can be separated by applying a pressure equal to or higher than the osmotic pressure corresponding to the solute concentration to the water to be treated.

  In a membrane filtration system using an RO membrane, it is common to perform pretreatment for removing insoluble components contained in water to be treated. For example, when seawater is desalinated, the turbidity, algae, microorganisms, etc. contained in the seawater are removed by pretreatment, thereby reducing the pollution load on the RO membrane and reducing the number of times the RO membrane is chemically washed. , Enabling stable operation over a long period of time.

  For pretreatment, it is common to use a film that can remove insoluble components. However, if many insoluble components accumulate in the pretreatment film used in the pretreatment, the pretreatment film is washed. Need to do.

JP 2007-289940 A JP 2009-240903 A JP 2007-289899 A JP 2008-289959 A JP 2011-16044 A JP 2011-62632 A JP 2011-72939 A

  However, it is difficult to remove the insoluble component accumulated in the pretreatment, and there is a problem that the energy required for removing the insoluble component is increased.

  Therefore, this invention provides the membrane filtration system which can improve the washing | cleaning efficiency of the pre-processing membrane used with a reverse osmosis membrane.

  The membrane filtration system according to the embodiment includes a pretreatment membrane, a high-pressure pump, a reverse osmosis membrane, and a fine bubble generator. The pretreatment membrane removes insoluble components contained in the water to be treated. The high-pressure pump applies pressure to the water to be treated from which insoluble components have been removed by the pretreatment membrane. The reverse osmosis membrane separates water to be treated, which has been given pressure by a high-pressure pump, into treated water from which soluble components contained in the water to be treated have been removed and concentrated water in which soluble components have been concentrated. The fine bubble generating device introduces concentrated water discharged from the reverse osmosis membrane at a high pressure to generate fine bubbles, and supplies the concentrated water containing fine bubbles to the pretreatment membrane being cleaned.

It is the schematic explaining the structure of the membrane filtration system which concerns on 1st Embodiment of this invention. It is the schematic explaining the structure of the membrane filtration system which concerns on 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same components are denoted by the same reference numerals and the description thereof is omitted. A membrane filtration system according to an embodiment of the present invention uses a RO membrane (reverse osmosis membrane) to desalinate salts and ions from seawater, brackish water, groundwater, and the like containing salts and ions, and at the front stage of the RO membrane This is a water treatment system having a function of cleaning the pretreatment film. Hereinafter, an example in which seawater is taken and desalinated will be described.

[First Embodiment]
As shown in FIG. 1, the membrane filtration system 1a of 1st Embodiment is the pre-treatment membrane which pre-processes the to-be-processed water introduced from the intake tank 11 which stores the to-be-processed water taken from the intake source, and the intake tank 11 12. A membrane filtration water tank 13 for introducing and filtering pretreated water to be treated, an RO membrane 14 for introducing treated water from the membrane filtration water tank 13 for desalination, and a treated water tank 15 for introducing fresh water from the RO membrane 14 I have. Further, the membrane filtration system 1a includes a fine bubble generating device 16 that generates fine bubbles using a part of the concentrated water. Furthermore, the membrane filtration system 1a may include an ultrasonic generator 17 that applies ultrasonic waves to the pretreatment membrane 12.

  The intake tank 11 stores seawater taken from the sea that is the intake source via the line L1 and the intake pump P1.

  The pretreatment membrane 12 is, for example, a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane) or the like, and water to be treated (stored in the intake tank 11 via the line L2 and the membrane filtration pump P2). Seawater) is introduced, and insoluble components contained in the water to be treated are removed from the water to be treated. The insoluble component remaining on the membrane surface of the pretreatment membrane 12 by filtration is removed from the pretreatment membrane 12 at the timing of backwashing. That is, insoluble components such as turbidity in seawater, microorganisms, organic matter with high viscosity released by microorganisms, dissolved organic matter, or inorganic ions accumulate on the membrane surface of the pretreatment membrane 12. When a large amount of such insoluble components accumulates, the pretreatment film 12 is clogged and the differential pressure increases. Therefore, in order to eliminate clogging in the pretreatment film 12, cleaning water is fed from the reverse side (secondary side) of the film at regular intervals to remove dirt adhering to the film surface (back washing). There is a need to.

  In the membrane filtration water tank 13, the water to be treated treated with the pretreatment membrane 12 is introduced through the line L3. A part of the water to be treated in the membrane filtration water tank 13 is passed from the membrane filtration water tank 13 to the pretreatment membrane 12 via the line L8 and the backwash pump P5 at the timing of backwashing.

  RO membrane 14 introduces the treated water treated in membrane filtration water tank 13 through line L4, water pump P3 and high-pressure pump P4, and filtered water from which salts and ions contained in the treated water are removed, Separated into concentrated water containing salts and ions. In order to process with the RO membrane 14, it is necessary to apply a pressure higher than the osmotic pressure of the solute. Therefore, in the membrane filtration system 1a, not only the water to be treated is fed by the water pump P3, but the water to be treated is set to a pressure (for example, about 5 to 6 MPa) higher than the osmotic pressure of salts and ions by the high pressure pump P4. It will be necessary to send it to the RO membrane 14 later.

  The fresh water obtained by the RO membrane 14 is sent to the treated water tank 15 through the fresh water line L5 and used as domestic water, industrial water, agricultural water, or the like. The concentrated water separated from the fresh water by the RO membrane 14 is discharged, for example, to the sea as a water intake source through the concentrated water line L6 and the pressure reducing valve B. Since the RO membrane 14 treats the water to be treated at a high pressure, the concentrated water discharged from the RO membrane 14 is at a high pressure. A part of the concentrated water discharged from the RO membrane 14 is supplied to the fine bubble generating device 16 via a line L7 branched from the concentrated water line L6.

  When a part of concentrated water discharged from the RO membrane 14 is introduced through the line L7 branched from the concentrated water line L6, the fine bubble generating device 16 generates fine bubbles used for backwashing the pretreatment membrane 12. . For example, the fine bubble generating device 16 takes in ambient air and generates fine bubbles such as microbubbles and nanobubbles using a shock wave method, a swirl method, or the like. Since the concentrated water is discharged from the RO membrane 14 at a high pressure, the power necessary for the microbubble generator 16 can be reduced by using the pressure of the concentrated water discharged from the RO membrane 14.

  The ultrasonic generator 17 is connected to the pretreatment film 12 and generates ultrasonic waves when the pretreatment film 12 is backwashed.

<Cleaning of pretreatment film>
In the membrane filtration system 1a, backwash water is supplied from the secondary side of the pretreatment membrane 12 when the pretreatment membrane 12 is backwashed. Specifically, in the membrane filtration system 1a, the membrane filtrate in the membrane filtration water tank 13 is supplied as backwash water via the line L8 and the backwash pump P5. Thereby, in the pretreatment film | membrane 12, the adhering substance on the film | membrane surface is peeled.

  Moreover, in the membrane filtration system 1a, in addition to the membrane filtrate in the membrane filtration water tank 13, fine bubble-containing water containing fine bubbles generated by the fine bubble generator 16 is supplied to the pretreatment membrane 12 via the line L9. . Thereby, in the pretreatment film | membrane 12, since a film | membrane surface can be wash | cleaned using a microbubble, compared with backwashing using only membrane filtration water, cleaning efficiency can be improved.

  Here, the fine bubbles have, for example, the characteristics (1) to (3).

  (1) The bubble diameter is small and the surface area per unit volume is large.

  (2) There is a self-pressurizing effect. That is, it is an effect that bubbles are reduced and disappear. In general, bubbles of 50 μm or less become smaller and disappear due to their shrinking action. At this time, the inside of the bubble disappears at a high temperature and high pressure.

  (3) It is negatively charged. Therefore, it is difficult for the bubbles to coalesce.

  In addition, fine bubbles cause phenomena such as an increase in gas dissolution efficiency, adhesion, reduced specific gravity, sustainability, diffusivity, or collapse (a type of cavitation) due to the characteristics (1) to (3). Among these phenomena, the reduction effect of pathogenic microorganisms and viruses has been confirmed by the phenomenon of crushing, and the efficiency of backwashing can be improved by the crushing.

  Although generation of fine bubbles requires a large amount of power, in the membrane filtration system 1a, the water to be treated is at a high pressure in order to allow the RO membrane 14 to permeate. Therefore, the membrane filtration system 1a generates fine bubbles by effectively using the concentrated water discharged at a high pressure for filtration through the RO membrane 14.

  The fine bubble generator 16 has a function of reducing the high-pressure concentrated water in the line L7 to a pressure suitable for generating fine bubbles, for example, about 1 MPa. The fine bubble generating device 16 can supply only the concentrated water not containing fine bubbles to the pretreatment membrane 12 by stopping the generation of fine bubbles by interrupting the mixing of air into the concentrated water. Moreover, the fine bubble generator 16 can also control the size of the fine bubbles to be generated by adjusting the mixing of air. As described above, in the membrane filtration system 1a, it is possible to obtain a higher cleaning effect by interrupting or adjusting the mixing of air in the fine bubble generating device 16.

  For example, the amount of air mixed into the concentrated water in the fine bubble generator 16 is adjusted to change the bubble diameter of the fine bubbles to generate fine bubbles having different sizes. In the membrane filtration system 1a, the effect of backwashing can be improved by washing the pretreatment membrane 12 using fine bubbles of different sizes. Specifically, in the initial stage of cleaning, the amount of air mixed in is reduced to generate fine bubbles having a small bubble diameter, and the bubbles enter the inside of the film. In addition, as cleaning progresses, it is conceivable to increase the amount of air mixed in and promote separation of turbidity and the like with fine bubbles larger than the initial stage.

  In the membrane filtration system 1a, the fine bubble-containing water may be supplied only from the secondary side of the pretreatment membrane 12, the fine bubble-containing water may be supplied only from the primary side of the pretreatment membrane 12, or the primary You may supply fine bubble containing water from both a side and a secondary side. For example, by supplying fine bubble-containing water not only from the secondary side, but also from the primary side or from both the primary side and the secondary side, the surface of the membrane and dirt attached to the inside of the membrane are effectively removed. be able to.

  After washing the pretreatment film 12, washing wastewater containing turbidity is discharged from the pretreatment film 12 and processed.

  The membrane filtration system 1a may generate ultrasonic waves with the ultrasonic generator 17 when cleaning the pretreatment membrane 12, and may apply ultrasonic waves to the membrane filtered water or the water containing fine bubbles. By applying ultrasonic waves, the cleaning effect can be improved as compared with the case where the membrane is cleaned only with membrane filtered water or fine bubbles.

  It is known that ultrasonic cleaning is highly effective in removing adhered substances and the like. Moreover, since crushing (disintegration) of fine bubbles can be promoted by ultrasonic waves, in the membrane filtration system 1a, OH radicals having high oxidizing power are generated around the fine bubbles, and the OH radicals adhere to the film surface. By reacting with turbidity or the like, the cleaning effect on the film surface can be enhanced. In order to utilize this crushing phenomenon of the fine bubbles, it is possible to obtain a higher cleaning effect by allowing the fine bubbles to penetrate not only the surface of the membrane but also the inside of the membrane. Therefore, in the membrane filtration system 1a, the fine bubble generator 16 generates fine bubbles having a small bubble diameter, and the ultrasonic waves are applied to the inside of the membrane to obtain a higher cleaning effect. be able to.

  As described above, the membrane filtration system 1 a according to the first embodiment uses fine bubbles generated by using the pressure used in the RO membrane 14 for cleaning the pretreatment membrane 12. Thereby, the cleaning efficiency of the pretreatment film 12 can be improved without using a new power source for generating fine bubbles. At this time, the size of the microbubbles generated by the microbubble generator 16 is adjusted according to the size of the pretreatment film 12 or the like, or the microbubble generator 16 generates microbubbles of different sizes, and these are different. The cleaning efficiency can be improved by adjusting the timing of supplying the fine bubbles having the size.

[Second Embodiment]
As shown in FIG. 2, the membrane filtration system 1b of 2nd Embodiment differs in the point provided with the microbubble containing water tank 18 compared with the membrane filtration system 1a mentioned above using FIG. In this membrane filtration system 1b, when the pretreatment membrane 12 is backwashed, after the fine bubble-containing water discharged from the fine bubble generator 16 via the line L9 is stored in the fine bubble-containing water tank 18, After joining the line L8 via the line L11, it is supplied to the pretreatment membrane 12 together with the membrane filtrate through the backwash pump P5.

  In the membrane filtration system 1b according to the second embodiment described above, it is possible to continue the cleaning using the fine bubbles even at the timing when the RO membrane 14 is not filtered. In addition, when the membrane filtration system is large and has a plurality of pretreatment membranes and RO membranes, and the pretreatment membrane and the RO membrane are not in a one-to-one pair, a single RO membrane is converted into a plurality of pretreatment membranes. It becomes necessary to inject fine bubbles. Therefore, when the fine bubble-containing water is directly supplied from the fine bubble generator 16 to the pretreatment film 12, the adjustment of pressure and flow rate is complicated, and therefore, it is possible to generate fine bubbles and store the fine bubble-containing water in advance. Useful.

  In the membrane filtration system 1b according to the second embodiment, fine bubbles generated using the pressure used in the RO membrane 14 are used for cleaning the pretreatment membrane 12 as in the membrane filtration system 1a according to the first embodiment. We are using. Thereby, the cleaning efficiency of the pretreatment film 12 can be improved without using a new power source for generating fine bubbles.

  As mentioned above, although this invention was described by each embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. Further, the present invention naturally includes various embodiments not described herein.

DESCRIPTION OF SYMBOLS 1a, 1b ... Membrane filtration system 11 ... Intake tank 12 ... Pretreatment membrane 13 ... Membrane filtration water tank 14 ... RO membrane 15 ... Treated water tank 16 ... Fine bubble generator 17 ... Ultrasonic generator 18 ... Fine bubble containing water tank

Claims (6)

A pretreatment film for removing insoluble components contained in the water to be treated;
A high-pressure pump that applies pressure to the water to be treated from which insoluble components have been removed by the pretreatment membrane;
A reverse osmosis membrane that separates water to be treated, which has been pressurized by the high-pressure pump, into treated water from which soluble components contained in the treated water have been removed, and concentrated water in which soluble components are concentrated;
A fine bubble generator that introduces concentrated water discharged from the reverse osmosis membrane at high pressure to generate fine bubbles, and supplies the concentrated water containing fine bubbles to the pretreatment membrane being cleaned;
A membrane filtration system comprising: A pretreatment film for removing insoluble components contained in the water to be treated;
A high-pressure pump that applies pressure to the water to be treated from which insoluble components have been removed by the pretreatment membrane;
A reverse osmosis membrane that separates water to be treated, which has been pressurized by the high-pressure pump, into treated water from which soluble components contained in the treated water have been removed, and concentrated water in which soluble components are concentrated;
A fine bubble generator that introduces concentrated water discharged at high pressure from the reverse osmosis membrane and generates fine bubbles;
A microbubble-containing water tank for storing concentrated water containing microbubbles generated by the microbubble generator;
A pump for feeding the concentrated water stored in the water tank containing fine bubbles to the pretreatment membrane at the timing of washing the pretreatment membrane;
A membrane filtration system comprising: An ultrasonic generator that applies ultrasonic waves generated by generating ultrasonic waves to the pretreatment film when the pretreatment film is washed;
The membrane filtration system according to claim 1 or 2. The membrane filtration system according to any one of claims 1 to 3, wherein concentrated water containing fine bubbles is supplied from a primary side of the pretreatment membrane during cleaning of the pretreatment membrane. When cleaning the pretreatment membrane, switching between supplying concentrated water containing fine bubbles from the primary side of the pretreatment membrane and supplying concentrated water containing fine bubbles from the secondary side of the pretreatment membrane. The membrane filtration system according to any one of claims 1 to 3, wherein the membrane filtration system is characterized. The membrane filtration system according to any one of claims 1 to 5, wherein the fine bubble generating device generates fine bubbles having a plurality of different sizes by adjusting an amount of air mixed therein.

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