JP2000061472A - Method and device for removing fine particles in water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively collect fine particles in water and also to remove uncharged particles by providing electrodes facing each other, a restriction part of an electric field formed between the electrodes, a liquid passing device for causing water to be treated to flow to between the electrodes, and a power source device for applying voltage to between the electrodes. SOLUTION: Since when high voltage pulses are applied, an electric field is formed between an anode 1 and a cathode 2, but a restriction part of the electric field is formed in openings 5a, 5b of insulating sheets 6a, 6b, fine particles in water move toward the part by dielectrophoresis to hold them in filter medium 3. In this case, since the dielectrophoresis moves the particles to a part of high electric field density irrespective of polarity of the electrodes, they are collected on both the insulating sheets 6a, 6b. By applying pulses of positive polarity, electrophoresis is caused to move the particles having negative charge to the anode side and to catch them. Negatively charged particles are thus moved more to the anode 1 side than to the cathode 2 side and are caught. Since two phenomena of dielectric dielectrophoresis and electrophoresis thus occur at the same time, particles can effectively move.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for removing fine particles existing in water by dielectrophoresis, and more particularly to a method and apparatus for removing fine particles existing in high-purity water such as pure water and ultrapure water. It is a thing.

[0002]

2. Description of the Related Art Ultrapure water used in semiconductor manufacturing processes, medical material manufacturing processes, etc. removes not only water-soluble substances such as salts and organic substances but also water-insoluble particles and microparticles such as microorganisms. . Such ultrapure water is manufactured by demineralizing with an RO (reverse osmosis) device or the like to produce pure water, and the pure water is sub-processed including an ion exchange device, an oxidation treatment device, a UF (ultrafiltration) device and the like. It is processed by the system to obtain ultrapure water.

In the process of producing high-purity water such as pure water and ultrapure water, when the water to be treated contains fine particles when the treatment is carried out by a membrane separation device such as an RO device or a UF device, In addition to clogging of the surface, microorganisms are trapped on the surface of the membrane and proliferate, contaminating the surface of the membrane and treated water. For this reason, it is necessary to remove microorganisms in the water before the membrane separation device.

Further, after such a treatment, if another treatment such as ion exchange is performed, fine particles may be generated along with the treatment, so the fine particles may be generated immediately before sending the treated water to the point of use. Need to be removed. Further, when the treated water is circulated in the treatment system, fine particles are generated in the system, and in particular, since microorganisms grow in the system and are mixed in water, it may be necessary to remove the fine particles even in such a circulation system. is there.

Conventionally, as a method of removing fine particles in water, a method has been proposed in which a voltage is applied between opposing electrodes to collect fine particles on the electrodes and remove them (for example, Japanese Patent Laid-Open No. 61-1).
87989). This method is a so-called electrophoretic method, in which particles are charged in a uniform and even electric field to collect and remove fine particles at an electrode. In order to move the particles, it is necessary to apply a high voltage. There is a problem that uncharged fine particles cannot be collected.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for removing fine particles in water, which are capable of efficiently moving and collecting fine particles existing in water and removing uncharged particles. It is to propose.

[0007]

The present invention is the following method and apparatus for removing fine particles in water. (1) A narrowed portion of an electric field formed between opposing electrodes is formed, treated water is flown between the electrodes, and a voltage is applied between the electrodes to capture fine particles in water by dielectrophoresis. Method of removing fine particles in water. (2) The method according to (1) or (2) above, wherein a high-voltage pulse is applied between opposing electrodes to trap fine particles in water by dielectrophoresis and electrophoresis. (3) The method according to (1) above, wherein the water to be treated is high-purity water. (4) A device for removing fine particles in water, which includes electrodes facing each other, a narrowed portion of an electric field formed between the electrodes, a liquid passing device for flowing water to be treated between the electrodes, and a power supply device for applying a voltage between the electrodes. .

In the present invention, the water to be treated to be treated is water containing fine particles, but particularly high purity water such as pure water and ultrapure water is suitable. Such high-purity water preferably has a specific electric conductivity of 100 μS / cm or less. The treatment according to the present invention is intended to treat water before or after a membrane separation device such as an RO device or a UF device in an ultrapure water production system, just before sending treated water to a point of use, or treating water in a circulating system of treated water. Preferably.

The fine particles to be removed include insoluble inorganic or organic particles existing in the water to be treated, microorganisms such as bacteria, etc., which are originally contained in the water to be treated and also from the outside during the treatment. Those which are mixed or generated, and those which are mixed in the system by peeling from the vessel wall and the like are included. These particles may be charged particles or uncharged particles. The particles to be removed have a particle size of 0.1 to 100 μm, preferably 0.1 to 10 μm.

In the present invention, such fine particles are passed between the opposing electrodes and collected by the electrodes by dielectrophoresis to be removed from the water to be treated. For charged particles, electrophoresis may occur together with induction migration. Electrophoresis is a phenomenon in which charged particles move toward an electrode having an opposite charge in an electric field, and occurs in both a uniform electric field and a non-uniform electric field.

On the other hand, in dielectrophoresis, a dielectric substance placed in an inhomogeneous electric field is polarized, and particles are moved by the force generated by the interaction between the induced dipole and the electric field. In this case, the fine particles move in the narrowed portion of the electric field, that is, the portion where the lines of electric force are concentrated, and are collected in the electrode. Electrophoresis must be DC or rectified pulses, but dielectrophoresis can be AC or pulsed.

In the present invention, in order to perform such dielectrophoresis, an electric field diaphragm is formed between the opposing electrodes. The narrowed portion of the electric field is a portion where the electric field is concentrated, and the density of the lines of electric force becomes high in this portion, and the particles move toward this portion and are collected. When the plate-shaped electrodes are opposed to each other, particularly when the flat-plate-shaped electrodes are opposed to each other in parallel, an insulating material such as a punching sheet of tetrafluoroethylene resin, a sheet having an opening such as a net or a grid is interposed between the electrodes. The electric field is concentrated in the opening to form a diaphragm. A filter paper, a filter cloth, or the like may be provided on the electrode surface or between the electrodes to form the narrowed portion of the electric field. Such an insulator sheet is preferably placed near the electrodes. The insulator sheet may be arranged only near the electrode on one side or near the electrodes on both sides, but it is preferable to arrange the insulator sheet on both sides because the narrowed portions are formed on both sides. Further, not only in the vicinity of the electrodes but also in the space between the electrodes, a squeezing portion is formed even if a filter paper or an insulating sheet is installed, which is preferable.

In addition, as the diaphragm portion, by forming irregularities on one electrode plate and providing an edge portion, the electric field is concentrated on the edge portion to form the diaphragm portion of the electric field. Such a counter electrode may be a parallel plate electrode or a concentric cylindrical cylinder type. In the case where the needle-shaped electrode is provided so as to face the plate-shaped electrode, the electric field is concentrated on the needle-shaped electrode to form the narrowed portion.

It is preferable that the narrowed portions of such an electric field are evenly distributed over substantially the entire area along the electrode gap of the counter electrode. For example, when an insulating sheet having an opening is interposed between the electrodes, It is preferable that the openings provided in the insulating sheet are arranged uniformly over almost the entire area of the insulating sheet. Also, when forming an edge portion with a concavo-convex portion on one electrode, or when using one electrode as a needle-shaped electrode,
It is preferable that the edge portion and the needle-shaped electrode are evenly arranged over the entire area of the other electrode surface. Further, it is preferable to make the diaphragm portion of such an electric field the same size because the removal efficiency is improved when the size is the same as the particles to be removed.

As the material of the electrode, stainless steel or thorium alloy can be used for both the anode and the cathode, but in order to prevent the elution of electrode components into the liquid, it is possible to use ferroelectric ceramics such as barium titanate. it can.
Fluorine resin (for example, polytetrafluoroethylene) is used as an insulator sheet having openings to be interposed between electrodes.
Besides, glass and ceramics can be used.

Each electrode surface is preferably provided with a filter medium for holding the collected particles. This filter material is made of filter paper, filter cloth, or the like, and as the material, paper, non-woven fabric of tetrafluoroethylene resin, or the like can be used. The strong electric field portion is also formed in the micro region by the filter medium. Such a filter medium is preferably provided in close contact with the electrode surface, and the opening insulator is preferably provided close to the filter medium.

As a power supply device for applying a voltage between the electrodes, there are a DC power supply, an AC power supply, a high voltage pulse power supply and the like, but a high voltage pulse power supply is preferable. Frequency 1 in case of alternating current
0 to ^{10 10} Hz, preferably 10 ⁵ to 10 ⁸ Hz, voltage 1
0V to 100kV, preferably 50V to 100kV, peak voltage 100V to 100k in case of high voltage pulse power supply
V, preferably 1 kV to 50 kV, pulse width 10 ^-9 to 1
It can be 0 ^-3 seconds, preferably 10 ^-6 to 10 ^-3 seconds. The power supply may be half-wave rectified using a diode.

The power supply device can be switched so that it is turned on during processing and turned off during cleaning and during rest, but a reverse voltage can be applied during cleaning.

The liquid passing device for passing the liquid to be treated between the electrodes is
During treatment, the treatment liquid is introduced from the supply liquid passage on one end side of the electrode gap, the treatment liquid is taken out from the treatment liquid passage on the other end side, the cleaning liquid is supplied from the cleaning liquid passage at the time of cleaning, and the cleaning waste liquid is discharged from the cleaning discharge passage. To be configured.

When the liquid to be treated is passed between the electrodes by the liquid passing device while the voltage is applied between the electrodes by the power supply device,
By dielectrophoresis, and in some cases by dielectrophoresis and electrophoresis, the fine particles in the water move to the narrowed portion of the electric field, and are collected and removed by the electrodes. The treatment liquid from which the particles have been removed is taken out from the treatment liquid passage.

The particles collected on the electrodes are retained by the filter medium, but if they accumulate in large quantities, they will leak out together with the treated water, so washing is performed intermittently. For cleaning, the particles that have accumulated near the electrodes can be washed away by stopping the application of voltage and flowing a washing solution, but at this time, a reverse voltage may be applied. The liquid to be treated may be used as the cleaning liquid, or the treatment liquid may be used.

Even if a DC voltage is applied, the particles can be removed by electrophoresis and dielectrophoresis. In this case, however, gas is generated by electrolysis and the collected particles are dispersed.
It is preferable to apply a high voltage pulse or an alternating voltage.
In particular, by applying a high voltage pulse, generation of gas can be prevented and electrophoresis and dielectrophoresis can be performed.

[0023]

According to the present invention, since particles in water are collected and removed by dielectrophoresis, particles present in water can be efficiently moved and collected with less power consumption than electrophoresis. It is possible to remove uncharged particles.

Further, by applying a high voltage pulse between the electrodes, the particles can be moved by electrophoresis without generating a gas, and the particles can be removed more efficiently by using both dielectrophoresis and electrophoresis. be able to.

When such a method is applied to high-purity water such as pure water or ultrapure water, it is possible to remove particles efficiently with a low electric power consumption because of its low electrical conductivity.
It is possible to prevent contamination of the membrane separation device such as UF.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an underwater particle removing apparatus of an embodiment.

In FIG. 1, A is an underwater particle removing device in which parallel plate electrodes composed of an anode 1 and a cathode 2 are provided so as to face each other. The facing electrode surfaces 1a and 2a of the anode 1 and the cathode 2 are smooth surfaces, and filter materials 3 and 4 such as filter paper and filter cloth are provided in close contact with each other. Then, the opening 5 is formed close to one electrode (anode 1).
An insulating sheet 6a having a is provided in close contact with the filter medium 3, and an insulating sheet 6b having an opening 5b in close proximity to the other electrode (cathode 2) is provided in close contact with the filter medium 4.
The openings 5a and 5b are evenly provided along the electrode gap 7 over substantially the entire surfaces of the electrodes 1 and 2 to form a diaphragm for the electric field.

A power supply unit 10 having an AC power supply 8 and a rectifier 9 is connected between the electrodes, the cathode side is grounded, and a positive high voltage pulse is applied. The liquid passage 11 to be treated is connected to one side of the electrode gap 7, and the treatment liquid passage 12 is connected to the other side thereof. Similarly, the cleaning liquid passage 13 is connected to one side of the electrode gap 7, and the cleaning drainage passage 14 is connected to the other side.

In the method of removing fine particles in water by the above apparatus, a high voltage pulse having a positive polarity is applied between the anode 1 and the cathode 2 by the power supply device 10, and the liquid to be treated is introduced into the electrode gap 7 from the liquid passage 11 to be treated. Then, the processing is performed while taking out the processing liquid from the processing liquid passage 12. At this time, an electric field is formed between the anode 1 and the cathode 2, but the openings 5a, 5 of the insulating sheets 6a, 6b are formed.
Since the narrowed portion of the electric field is formed in b, the particles in the water move toward this portion by dielectrophoresis and are held by the filter medium 3. In this case, the dielectrophoresis causes particles to move to a portion where the electric field density is high regardless of the polarity of the electrodes, so that the insulating sheets 6 on both sides are
Gather at a and 6b.

By applying a positive pulse here, electrophoresis also occurs, and the negatively charged particles move to the anode side and are captured. Therefore, the negatively charged particles move toward the anode 1 side rather than the cathode 2 side and are captured. In this way, two phenomena of dielectrophoresis and electrophoresis occur at the same time, so that the particles move efficiently and are captured by the filter medium 3 on one electrode side. Then, the voltage is intermittently applied to prevent electrolysis, thereby preventing gas from being generated and performing the treatment.

In this way, since the fine particles in the water to be treated move toward the anode 1 and the cathode 2 and are collected, the treated water from which these fine particles have been removed is taken out from the treatment liquid passage 12. When the treatment progresses and a large amount of fine particles are captured, a part of the fine particles leaks into the treated water, so the treatment is stopped and the cleaning is performed.
The cleaning method is performed by stopping the application of the voltage, flowing the cleaning water from the cleaning liquid passage 13, and discharging the cleaning drainage from the cleaning drainage passage 14. Since the electric attraction of the electrodes disappears when the voltage application is stopped, the fine particles are easily washed away by the washing water.
At this time, by applying a reverse voltage, the separation of the fine particles can be promoted. It is preferable to use treated water (ultra pure water) as the washing water.

FIG. 2 is a block diagram showing an underwater particulate matter removing apparatus of another embodiment. In this embodiment, the opposing anode 1
And recesses 1 on the opposing electrode surfaces 1a, 2a of the cathode 2.
b, 2b are formed, and the edge portion 1 is formed at the boundary with the reference plane.
c, 2c are formed, and the edge portions 1c, 2c form the diaphragm portion of the electric field. Also in this case, the electrode surface 1a,
Filter media (3, 4) can be provided along 2a,
Here, in order to explain the phenomenon of dielectrophoresis, the state without a filter medium is shown. Reference numeral 15 is a particle, showing an example observed with a microscope.

FIG. 2 (a) shows a state before voltage application. Particles 15 existing between the electrodes 1 and 2 are scattered and move in random directions by Brownian motion.
(B) shows the state at the start of high voltage pulse application.
No. 5 begins to bead-shaped to agglomerate along the lines of electric force. (C) shows a state in which the high voltage pulse is being continuously applied, in which the agglomerated particles 15 move toward the edge portion 1c which is the narrowed portion of the electric field,
It adheres to the electrode surface 1a. Such a phenomenon was confirmed with latex beads, Escherichia coli cells, and activated carbon powder.

FIG. 3 is a flow chart showing the ultrapure water production system. In FIG. 3, 21 is a primary pure water system, and 22 is a subsystem. The primary pure water system 21 is a system for producing primary pure water from raw water, and includes an RO device 23,
The primary pure water manufactured in 3 is connected to the sub tank 24 so as to be supplied. The subsystem 22 is a system for producing ultrapure water from primary pure water. The primary pure water is pumped from the subtank 24 by a pump 25, cooled by a heat exchange device 26, oxidized by a UV oxidation device 27, and deoxidized. Deionization is performed by the ion devices 28 and 29, and UF film treatment is performed by the UF device 30 to produce ultrapure water. The produced ultrapure water is sent from the water supply passage 31 to the use point 33, and is circulated in the circulation passage 32.
It is in contact with the sub tank to circulate it.

In such an ultrapure water production system, before the RO device 23 of the primary pure water system 21, in front of the UF device 30 of the subsystem 22, in front of the use point 33, and in front of the sub-tank 24, the above-mentioned figure is used. 1 or the particle removing device A1, A2, A3, A4 shown in FIG. 2 is installed to remove fine particles in the water to be treated. As a result, in the case of A1 and A2, R
Prevents film contamination of the O device 23 and the UF device 30,
In the case of 3 and A4, the use point 33 or the fine particles in the circulating ultrapure water are removed.

In addition, RO or UF such as wafer polishing drainage and CMP drainage discharged from the use point
In a system for treating a permeable membrane such as a membrane, by providing the underwater particle removing device A before the membrane treatment, it is possible to remove fine particles and thereby prevent the permeable membrane from being contaminated. In this case, even if a large amount of fine particles are contained, it can be removed.

[0037]

EXAMPLES Examples of the present invention will be described below. Example 1 Removal of Latex Particles in Pure Water Aluminum parallel plate electrodes were used as an anode and a cathode (size 5 cm × 10 cm, distance between electrodes 3 mm),
Filter paper (thickness: 10 μm) was attached to each of them, and a punching sheet of fluororesin (polytetrafluoroethylene) was attached to the anode in order to reduce the electric field. The power supply uses an inverter neon transformer (frequency 26 kHz),
Rectify the output with a diode and take out the positive component,
A peak voltage of 500 V was applied. On the other hand, spherical particles having a diameter of 1 μm were used as the latex particles, and 4.9 × 10
^It was suspended in pure water at a temperature of ⁶ cells / ml. 3 this solution
Water was passed through the chamber at a rate of ml / min, and the particle concentration after the treatment was measured. As a result, the particle concentration before treatment was 4.
9 × 10 ⁶ particles / ml, particle concentration 1.5 after treatment
× 10 ⁴ cells / ml, and the water particles by the high voltage process was able to remove 99.7%. This treatment also caused electrolysis to generate a very small amount of gas, but did not affect the collection of particles.

Example 2 Removal of microbial cells in pure water Treatment was carried out under the same electrode, power supply and liquid passing conditions as in Example 1.
As a microbial cell, Escherichia coli was cultured in an LB medium and the collected cells were suspended in pure water to prepare a sample. As a result, the concentration of particles (bacteria) was 5 × 10 ⁶ particles / ml before treatment, and the concentration of particles was 3000 / ml after treatment, and 99% of particles (bacteria) were treated by the particle removing device. It was possible to reduce the above.

Example 3 Removal of Silica from Silica-Containing Wastewater The silica-containing wastewater containing colloidal silica was diluted 10 times and treated under the same conditions as in Example 1. as a result,
The silica concentration was 25 mg / l before the treatment, and the silica concentration was 11 mg / l after the treatment, and the removal rate was 56%.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an underwater particle removal apparatus of an embodiment.

FIG. 2 is a configuration diagram of an underwater particle removal device of another embodiment.

FIG. 3 is a flow chart of an ultrapure water production system.

[Explanation of symbols]

1 anode 2 cathode 3, 4 filter media 5a, 5b opening 6a, 6b Insulation sheet 7 electrode gap 8 AC power supply 9 Rectifier 10 power supply 11 Liquid path to be treated 12 Processing liquid path 13 Cleaning liquid path 14 Cleaning drain 15 particles 21 Primary pure water system 22 Subsystem 23 RO equipment 24 sub tanks 25 pumps 26 Heat Exchanger 27 UV oxidizer 28, 29 Deionizer 30 UF device 31 water supply 32 circuit 33 Use Point

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Sosuke Nishimura             Kurita, 3-4-3 Nishi-Shinjuku, Shinjuku-ku, Tokyo             Industry Co., Ltd. (72) Inventor Tetsuo Mizuba             Kurita, 3-4-3 Nishi-Shinjuku, Shinjuku-ku, Tokyo             Industry Co., Ltd. (72) Inventor Akira Mizuno             1 of 2 Higashiura, Kitayama-cho, Toyohashi City, Aichi Prefecture F-term (reference) 4D061 AA02 AB15 BA02 BA10 BA13                       BB04 BB05 BB07 BB09

Claims (4)

[Claims] 1. An electric field diaphragm formed between opposing electrodes, water to be treated is flowed between the electrodes, and a voltage is applied between the electrodes to capture fine particles in water by dielectrophoresis. Method for removing fine particles in water. 2. The method according to claim 1, wherein a high-voltage pulse is applied between opposed electrodes to trap fine particles in water by dielectrophoresis and electrophoresis. 3. The method according to claim 1 or 2, wherein the water to be treated is high-purity water. 4. Particles in water comprising: opposed electrodes; an electric field diaphragm formed between the electrodes; a liquid passing device for flowing water to be treated between the electrodes; and a power supply device for applying a voltage between the electrodes. Removal device.