WO2001066238A1

WO2001066238A1 - Method of producing purified water

Info

Publication number: WO2001066238A1
Application number: PCT/JP2000/001318
Authority: WO
Inventors: Masahiro Kishi
Original assignee: Aquasystems Ltd.
Priority date: 1998-06-30
Filing date: 2000-03-06
Publication date: 2001-09-13
Also published as: JP2000079390A

Abstract

A method of producing purified water economically and safely by using a hollow fiber type ultrafiltration membrane formed in a filtration layer by regularly and overlappingly winding, to open uniformly, hollow yarn bundles around a core disposed at the center part of a vertical cylindrical type pressure vessel so that the core extends in the axial direction of the pressure vessel, characterized in that a filtration operation is of a full amount filtration and performed by supplying raw water from an outer peripheral space formed between the inner peripheral surface of the pressure container and the outer peripheral surface of the filtration layer to the core and draining filtrated water from the inside hollow of the hollow yarns, and the cleaning operation of the filtration layer including the membrane surface of the hollow yarns is performed by a basic cleaning comprising a back pressure cleaning in which the filtrated water flows from the inner hollow of the hollow yarns to the outside thereof and a reverse flow cleaning by the raw water (filtrated water may be used; applicable hereafter) supplied from the core to the outer peripheral space.

Description

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Specification

Water purification method Technical field

The present invention relates to a method for producing purified water from river water, brackish water, seawater and wastewater using a hollow fiber type ultrafiltration membrane. Here, purified water refers to water from which insoluble solids (including colloids; the same applies hereinafter) contained in raw water (river water, brine, seawater, and wastewater before filtration) are removed. Background art

Ultrafiltration membranes have high particle removal performance and can almost completely remove particles in raw water.Since their operation is simple, they are widely used industrially as turbidity-disinfection means for raw water. I have.

Specifically, alternatives to sand filtration in water treatment, pretreatment for obtaining fresh water from brackish water or seawater by the reverse osmosis membrane method, and means for removing insoluble solids from wastewater are typical examples. It is typical.

As the ultrafiltration membrane, a hollow fiber (also called a hollow fiber; a bundle of these bundles in a pressure vessel is generally used) is often used because of its large throughput per unit volume. .

However, in a conventional apparatus using a hollow fiber type ultrafiltration membrane, if filtration is continued for a long time, a space composed of bundles of the hollow fibers including the membrane surface of the hollow fibers (hereinafter referred to as “filtration layer”) ) Is contaminated and accumulates, and if a predetermined amount of filtered water is to be obtained, it must be operated at a high pressure. And if the contamination of this filtration layer progresses further, the filtration cannot be continued.

Therefore, at the time when the device shows a predetermined pressure rise, a measure is taken to wash the contaminated filtration layer with water (chemicals may be used if the contamination is severe). Since the operation of the apparatus, that is, the filtration operation, must be interrupted, it is desirable from the viewpoint of the operation efficiency of the apparatus to reduce the frequency of this washing and minimize the time required for washing. In the conventional system, as a measure, the filling rate of the hollow fiber bundle into the fillable space inside the pressure vessel is suppressed to 0.3 or less, and the insoluble solids in the raw water that has entered the inside of the filtration layer are easily discharged to the outside. A part of the raw water supplied to the pressure vessel is drawn out from the pressure vessel in order to make it possible to escape and to minimize the formation of an insoluble solid deposit inside the filter layer, and the primary water (raw water supply side) is taken out. Recirculation was used to increase the flow velocity on the primary side (the idea that the membrane surface should not be contaminated as much as possible).

In addition, the washing operation was generally performed by flowing filtered water (including water containing chlorine-containing chemicals) from the direction opposite to the water filtration direction (backwashing).

Such a conventional apparatus naturally has a limit in the throughput per unit volume, and moreover, the more the backwashing is performed, the more the filtered water is consumed, so that the recovered rate of the filtered water is reduced. Also, recirculation of raw water naturally raises power costs.

In addition, chlorine-based chemicals should be used to avoid contamination of hollow fiber membranes by microorganisms (including secretions-insoluble solids-hereinafter, unless otherwise specified) that are difficult to remove by ordinary washing. Filtration is also performed by adding to raw water, but this raises a new problem of trihalomethane formation depending on the quality of raw water.

An object of the present invention is to provide an economical and safe water purification method that solves the above-mentioned problems of the prior art. Disclosure of the invention

The present inventor has completed the present invention by carefully studying and verifying the factors of the problem including the pressure loss increase of the conventional system.

First, the throughput per unit volume was addressed by increasing the filling rate of the hollow fiber bundle. That is, a hollow fiber bundle is regularly and superimposedly wound around a core tube arranged at the center of a pressure vessel so as to extend in the axial direction thereof so as to have a uniform opening, and a hollow fiber type as a filtration layer is formed. An ultrafiltration membrane was used. The phrase "a hollow fiber bundle is regularly and superposedly wound around a core tube so as to form a uniform opening" is disclosed, for example, in the claims of Japanese Patent Publication No. 3-144492. Of the wound bundle of filaments Equivalent to. The aperture is a value obtained by calculation from the diameter of adjacent hollow fibers and the porosity of the space formed by the hollow fibers.

According to the conventional idea, when the ultrafiltration membrane of such an embodiment is used, the insoluble solids (including microorganisms and secretions thereof, which are the same hereinafter) once entering the inside of the filtration layer are easily removed from the layer. However, it has been considered that this is an unfavorable mode because it causes pressure loss due to the dense structure itself. However, the former is merely an assumption (in short, as a conventional pretreatment device). On the other hand, it was found that the latter can be dealt with by considering the method of passing water in the filtration operation and the method of cleaning the membrane surface.

That is, the present invention relates to a core tube (which has a large number of holes penetrating the entire wall thereof and has an outer peripheral surface formed in a central portion of a vertical cylindrical pressure vessel so as to extend in the axial direction thereof. In addition, the spacer includes a plurality of ribs arranged on the outer peripheral surface of the core tube in the axial direction thereof and a net covering the upper end surface of the rib. A water purification method using a hollow fiber type ultrafiltration membrane, which is used as a filtration layer by winding a bundle of hollow fibers regularly and superposedly so as to form a uniform opening, The filtration operation is total filtration, and raw water is supplied from the outer peripheral space formed between the inner peripheral surface of the pressure vessel and the outer peripheral surface of the filtration layer toward the core tube, and the hollow fiber By extracting filtered water from the lumen of the The washing operation of the filtration layer including the membrane surface of the hollow fiber is performed by back-pressure washing in which filtered water flows from the inner cavity of the hollow fiber to the outside thereof, and supply from the core tube toward the outer peripheral space. This is characterized in that it is carried out by a basic cleaning consisting of backwashing with raw water (may be filtered water; the same applies hereinafter). BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a system diagram showing one embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a structure of one embodiment of a membrane module used in the present invention (cut along an axis of a core tube. FIG. 3 is a substitute photograph showing the surface layer of one embodiment of the filtration layer of the membrane module used in the present invention, and FIG. FIG. BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, the flow direction of the raw water in the filtration operation is directed from the outer peripheral portion of the pressure vessel toward the center, and the method of extracting the filtered water from the inner cavity of the hollow fiber is adopted. (The pressure drop due to the flow velocity decreases toward the center. Further, the flow velocity becomes “zero” near the core tube due to the total filtration.) The particles do not move to the center and remain near the surface of the filtration layer.On the other hand, coarse particles having a particle size larger than the aperture of the hollow fiber bundle enter the surface of the filtration layer further. Blocked (these trapped particles (including those associated) themselves also act as additional filtration layers). Therefore, if the washing operation is performed properly (details will be described later), it is possible to easily cope with the pressure loss increase due to such trapped particles. The vertical type pressure vessel is used for removing the insoluble solids trapped in the filtration layer in a direction against gravity as in sand filtration (downward flowing water system) because of its efficiency. It is not a good idea in terms of.

Incidentally, the filling rate of the hollow fiber bundle constituting the preferable filtration layer with respect to the fillable space inside the pressure vessel is at least 0.5. The aperture of the hollow fiber bundle is usually about 100 m (the particle diameter of the insoluble solid that is prevented from flowing into the inside of the hollow fiber bundle surface is 30 m). ~ 50 rn). If the molecular weight cutoff of the hollow fiber is appropriately selected, even microorganisms can be trapped on the membrane surface, and if measures against contamination of the membrane surface of the hollow fiber can be taken properly, the filtration operation It is not necessary to constantly add a chlorine-based disinfectant to the raw water in the above. In the present invention, as described above, the filtration layer washing operation as the countermeasure includes back pressure washing in which filtered water flows from the lumen of the hollow fiber toward the outside thereof, and the outer periphery of the pressure vessel from the core tube. Backwashing, which consists of backwashing with raw water supplied to the space (hereinafter referred to as “basic washing”), is performed as needed, and empty washing (after the basic washing, from the core pipe, is performed). The water remaining in the pressure vessel containing the trapped matter of the filtration layer removed by this is excluding water in the lumen of the hollow fiber. Is discharged out of the device through the raw water inlet during the filtration operation), or Chemical washing (after the basic washing, the first flow of raw water (which may be filtered water; the same applies hereinafter) from the core tube containing hypochlorite ions thereinto toward the outer peripheral space. The washing is performed by washing the raw water (which may be filtered water; the same applies hereinafter) from the core tube with the acid contained therein toward the outer peripheral section. It is not necessary to add chlorine-based disinfectants to raw water during operation.

That is, a specific washing operation of the filtration layer in the present invention is performed in the following steps.

1. Basic cleaning

① Back pressure cleaning

Filtration operation from the lumen of the hollow fiber (raw water flows from the outer surface of the hollow fiber, that is, the membrane surface, to the lumen of the hollow fiber, and insoluble solids are separated on the membrane surface to become filtered water. Flow through the filter at a high pressure difference in the opposite direction (the hollow fiber itself and its pores expand). The main object to be cleaned is fine particles (specific cleaning effect is “excluded”) clogging the pores (approximately 7 nm) of the hollow fiber and the cake layer deposited on the membrane surface of the hollow fiber (specific cleaning effect is "Peeling"). Specific constituents of the fine particles and the cake layer are organic macromolecules such as metal hydroxide colloids and proteins.

② Backwashing

Using the core tube, the raw water flows in the opposite direction to the filtration operation from the inside to the outside of the filtration layer (the raw water flows from the outer space of the pressure vessel to the core tube in the direction of the core tube). The main object to be cleaned is the fine particles trapped inside the filtration layer, but, of course, the fine particles and the cake layer removed and peeled off in the previous back pressure cleaning are also discharged out of the apparatus system by this operation. In this operation, since the water is not moved into the hollow fiber lumen, the flow velocity is higher inside the filtration layer, which contributes to the removal of the object to be washed from the inside of the filtration layer.

2.Additional cleaning

① Empty washing

The fine particles trapped inside the filtration layer are suddenly blown out of the core tube by rapid jet of compressed air, and are completely converted into a high-speed gas-liquid multiphase flow (water remaining in the pressure vessel and air introduced into the core tube). And remove it outside the system. Since the drainage is done by air Recovery rate is improved. However, since the rejection force is so strong that the filtration membrane may be damaged, it is better to carry out the operation appropriately in view of the results of the basic washing and, if necessary, the chemical washing described later.

② Medicine washing

Even if the basic washing is repeated at appropriate intervals, a part of the metal hydroxide (which is almost completely removed by the filtration membrane) remains on the membrane surface and forms a cake layer together with the organic matter captured by the filtration membrane. I do. Further, the metal hydroxide precipitated in the pores of the hollow fiber and a part of organic macromolecules such as proteins trapped in the pores remain therein, so that the filtration resistance gradually increases. If the filtration resistance is within the limit, it is not necessary to remove all of the residual metal hydroxides, etc., but once dissolved, there is a risk of re-precipitation due to dilution, etc. It is imperative that hydroxide removal be performed almost perfectly. The specific steps are as follows.

A. First wash

a. Raw water containing hypochlorite ions is introduced into the pressure vessel through the same route as backwashing in the basic washing (first chemical passing process). Unlike the backwashing performed before this operation, the raw water containing hypochlorite ions introduced into the pressure vessel is also introduced into the secondary side of the hollow fiber through the pores of the hollow fiber. Here, the hypochlorite ion contained in the raw water cooperates with the metal hydroxide to mainly oxidatively decompose the organic substance that mainly forms a cake layer on the membrane surface and as a part of the organic substance. This is for killing microorganisms.

b. The introduced raw water containing hypochlorous acid is held in the pressure vessel for a predetermined time (first holding step). The purpose of this step is to make the oxidative decomposition of the organic substances and the disinfection of microorganisms effective with less chemicals.

c Flow the hypochlorite ion-containing raw water introduced into the secondary side of the hollow fiber through the same route as the back pressure cleaning in the basic cleaning (first back pressure washing step). The purpose of this step is to eliminate the organic substances that block the pores of the hollow fiber.

d. The raw water containing hypochlorous acid and the raw water not containing hypochlorous acid (filtrated water may be used in the same manner as described above) are used in the same way as the backwashing of the basic cleaning. Flow through the same route (first backwashing step).

In this way, the chemical solution (raw water containing hypochlorite ion) flows through the filtration layer in the opposite direction to the filtration operation, so that the inner perimeter of the filtration layer (water flow during the filtration operation is from the outer perimeter of the filtration layer). (The contamination level is lower than that on the outer side because it is directed toward the inner side.) The higher the flow rate, the more contact is made with a fresh chemical solution, and a cleaner filtration surface is maintained. There is almost no decrease in performance.

A. Second wash

This operation is performed in the same manner as in the first chemical washing except that hypochlorite ion is replaced with acid. Since the purpose of this operation is to remove the metal hydroxide, the acid may be any one that can supply a predetermined concentration of hydrogen ions to the washing water, and specifically, hydrochloric acid, sulfuric acid, nitric acid, etc. And some organic acids such as mineral acid and citric acid (preferably hydrochloric acid from the viewpoint of easy handling and availability).

According to the present invention, the contaminants on the membrane surface and the filtration layer containing microorganisms can be almost completely removed, so that they can be sufficiently used as a pretreatment operation for desalination treatment by reverse osmosis using brackish water or seawater as raw water. In addition, the filtered water produced in the present invention can be supplied to a reverse osmosis apparatus as it is (without requiring any further pretreatment). Further, as is clear from the characteristics, the system of the present invention can be naturally applied to a method for removing insoluble solids in wastewater as well as river water. It should be noted that priority is given to the convenience of explanation, and the membrane used in the system of the present invention has been described as an ultrafiltration membrane, but the idea of the present invention is that the molecular weight cut off of the membrane used is not a requirement, The applicable membrane is not limited to an ultrafiltration membrane, and for example, an MF membrane or an NF membrane may be used.

Hereinafter, the present invention will be described in detail with reference to the drawings showing one of the embodiments.

Fig. 1 shows the basic flow of the present invention (the flow for the original purpose of obtaining purified water in which insoluble solids are almost completely removed from the raw water, that is, the flow for the filtration operation). Here, V 0 is a raw water tank, VI is a pressure vessel, V 2 is a washing water tank, V 3 is an air reservoir (for compressed air), V 4 is a water purification tank, and P is a raw water pump. In the figure, "Chlorine" is indicated in the pressure vessel: _g

A chlorine-based chemical that is supplied only as a source of hypochlorite ion during the cleaning operation of the upper layer. Water purification tank: The downstream of V4 is where purified water is used, for example, in the case of clean water. It is a chlorine-based chemical that is added to satisfy the required residual chlorine concentration at the tap. Also, what is indicated as "hydrochloric acid" in the figure is hydrochloric acid as a representative of the acid that is supplied only during the operation of washing the filtration layer.

In the present invention, the raw water is raised to a predetermined pressure by the raw water pump: P, and then sent to the primary side of the pressure vessel: VI (the outer surface of the hollow fiber, that is, the side where the membrane surface is exposed). As shown in FIG. 2, inside the pressure vessel, a layer composed of a bundle of hollow fibers: UF (hereinafter, referred to as a filtration layer) is provided at the center thereof so as to extend in the axial direction thereof. It is wound and held regularly and superimposed so as to have a uniform opening around T (Fig. 3 shows the state of the surface layer, which is in the form of a certain woven fabric). On the other hand, the ends of the hollow fibers constituting the filtration layer (both ends in the drawing, but at least one end are sufficient) are divided into water-tight sections at S 1 and S 2 from the inside of the pressure vessel. Water chamber: VII, VI 2 whose inner cavity (which is the secondary side of the ultrafiltration membrane device) is open, so that the raw water introduced into the pressure vessel has the raw water inlet: I From: an outer peripheral space formed between the inner peripheral surface of the pressure vessel and the outer peripheral surface of the filtration layer: W enters the filtration layer and the membrane surface of each hollow fiber in the filtration layer Flows toward the core pipe while being filtered at the same time (here, since the core pipe is blinded by a shut-off valve provided in a pipe connected to the core pipe, The raw water is not directly discharged to the outside of the pressure vessel through this pipe, and the whole amount of the raw water supplied to the pressure vessel is filtered water, that is, purified water, and the raw water is piped from the water chamber. The water is discharged to the outside of the pressure vessel via a lid for forming a space as a water chamber: one end of which is connected to C 1 and C 2. (In this flow, pressurized air is used as a means for sending the washing water in the filtration layer washing operation, so this tank is provided between the water purification tank: V4. A pump may be used as the water supply means. The system for separately providing the washing water tank is composed of a pressurized air for performing high-speed washing, air washing and air washing in the membrane surface washing operation as described later. Another reason for this is that the reservoir has a separate reservoir.) It is first sent via appropriate means, for example a pump and piping.

On the other hand, when the predetermined filtration operation is completed, the filtration layer: UF becomes the surface layer of the filtration layer (the outer surface layer including the outer peripheral surface), the inside of the filtration layer, and on the membrane surface of each hollow fiber and in the pores. ) Enter a cleaning operation to remove insoluble solids trapped and adhered to the water. The washing operation consists of basic washing that is performed regularly at appropriate intervals and additional washing that is added to the washing as needed (see Fig. 4 for the route through which water or air flows).

(1) Basic cleaning

It is composed of “back-pressure washing” using filtered water previously stored in the washing water tank V 2, and “back-flow washing” performed following the back-pressure washing and using raw water as washing water. Note that all valves not specified in the following description shall be in the "closed" state.

1) Back pressure cleaning

Rinse water tank: Apply pressure to V2 (valve: CV5 "open"; CV7 is assumed to be "open" as long as an operation that requires air is performed) and stored in the rinse water tank in advance Filtered water is supplied to the water chambers: C1 and C2, and a predetermined pressure is applied from the hollow fiber lumen to the outer surface of the hollow fiber (in principle, three times the filtration pressure difference, specifically 300 to 500 kPa ) To flow the filtered water (valve: CV3 "open"). A washing time of 10 seconds is sufficient.

2) Backwash

Core pipe: From T to pressure vessel: Outer space of V1: Raw water flows toward W (valve: CV4 and CV3 "open", raw water pump: P operation). The washing water volume is 3 times the filtration layer space volume as standard. This operation is performed after “backwashing” is repeated several times.

(2) Additional cleaning

A high-speed compressed air (more precisely, a gas-liquid mixed phase flow of water and air) shocks the filtration layer and cleans the filtration layer. “Empty washing”, and “pharmaceuticals that use raw water containing chemicals” Washing ". As a general rule, “empty washing” and “medicine washing” are performed after performing one of the above basic washings several times. Of course, do both in series as needed ^ _Q

You may. In addition, “washing” refers to “first washing” (drug: a drug capable of releasing hypochlorite ions, such as sodium hypochlorite) and “second washing” (drug depending on the chemical used). : An acid, for example, a mineral acid such as hydrochloric acid or an organic acid such as citric acid) (performed in series in numerical order)).

1) Empty washing

Core tube: From the top of T, pressure vessel: V1 is pressurized (valve: CV6 "open") with compressed air (air reservoir: supplied from V3) of about 3 bar, and then valve: CV3 is opened. Drain the water inside the pressure vessel rapidly. The initial pressure: 500 kPa, the pressure at the completion of drainage: lbar is maintained, and the flow velocity in the filtration layer is as large as about 75 m / h even at the outer periphery (in the inner periphery, 28 Om / h) even if the washing is performed for several seconds. Therefore, the cleaning ability is sufficient.

2) washing

It consists of the following steps. Note that only the first wash is described below because the first wash is different from the second wash. (The second wash is described below.) The first of the description of the above shall be read as the second).

① First drug delivery process

From the core tube: T to the pressure vessel: Outer space of VI: Raw water impregnated with hypochlorite ion is flowed toward W (valve: 4 and 〇3 "open", raw water pump: P operation) When it is confirmed that the water in the internal space of the pressure vessel has been replaced with the raw water containing hypochlorite ion, the introduction of the raw water is stopped (the valves: CV4 and CV3 are closed, and the raw water pump: P is stopped). Here, in order to make hypochlorite ions contained in raw water, for example, sodium hypochlorite may be injected into raw water flowing into the pressure vessel at a predetermined ratio as shown in FIG. 20 ppm, preferably 5 to 1 Ορρπι In the case of “second chemical washing”, the pH (in this case, pH) is 2.5 to 4.0, and 2.7 to 3. 7). In addition, the completion of the water replacement is determined in advance by a valve: until the concentration of hypochlorous acid in the water discharged through the CV3 (in the case of the second washing, PH can be used) reaches a predetermined concentration. You just need to know the time and set that time in the timer. In this step, the raw water containing hypochlorite ions is also filled in the washing water tank: V2 through the pores of the hollow fiber (valve: CV2 is temporarily opened, and after a predetermined time elapses, a timer or Attach a liquid level controller to the washing water tank. Will be closed at the traffic light).

② First holding process

Hold the last state of the previous process for a predetermined time. (If the concentration of hypochlorite ion is 5 ppm, 5 minutes for ordinary water is sufficient. In the "second chemical washing," A pH of 3 and 5 to 10 minutes is sufficient).

③ First back pressure medicine wash

Washing water tank in the first pass-through process: Hypochlorite ion-containing raw water stored in V2 (filtered water because it passes through the membrane surface to be precise) is backwashed in basic washing. (Valve: 〇5 and 33 "Open")

④ First backwash step

Raw water pressure vessel in the first pass-through process: Raw water containing hypochlorite ions flows first, and raw water itself flows after a predetermined time, following the same route as the introduction to V1. Here, the presence or absence of the presence of hypochlorite may be determined by operating and stopping a chemical capable of generating hypochlorite in water, for example, a sodium hypochlorite injection pump (not shown).

The conditions for the standard washing operation (backwashing → backwashing – chemical washing) are as follows.

① Minimum cleaning interval (back-pressure cleaning): once 30 minutes (Condition: recovery rate is 95% or less)

(2) Maximum washing interval (back pressure washing): 3 hours for each time (condition is further recovery rate of 95% or more)

③ Backwash frequency: At least once Backwash four times ④ Chemical wash frequency: At least once Z 12 hours

[0 0 3 0]

Test example-1 (Confirmation of basic cleaning effect)

1. Raw water

Water (insoluble solids concentration: 2,000 ppm) in which kaolin (average particle size: 3 ^ m) was dispersed in tap water was injected into the tap water with a metering pump (target insoluble solids concentration). : 50 ~ 250. 2. Test equipment

See FIG. The detailed specifications of the membrane module (see Fig. 2. Specifically, model number: HM8AUF manufactured by Toyobo Co., Ltd. is used) are as follows.

① Outer diameter of pressure vessel: 5 B

② Membrane area: 38m2

③ Hollow fiber: (outside diameter) 300 ζπι, (inside diameter) 200 m

3. Exam

Water temperature: 23: Filtration pressure: 100 kPa, Filtration flow rate: 0.7 m3 / h for 1 hour and 52 minutes, and then washing operation was performed as follows.

(1) Back pressure washing (Washing water: Purified water in the washing water tank (volume: 5 L) obtained by the filtration operation. Water supply power: Air from the air tank-Pressure: 50 OkPa-Time: 10 seconds).

(2) Backwashing (washing water: raw water. Flow rate: 1.3 times the filtration operation. Time: 20 seconds).

4. Test results

(1) After 12 cycles of operation, the balance of the insoluble solids was examined. The recovery rate of the insoluble solids flowing into the equipment was over 99% (water recovery rate: 98.0%).

② The concentration of insoluble solids in the raw water was reduced to 67 ppm, the filtration operation time was extended to 6 hours, and the system was operated for 12 cycles, but there was no problem with no abnormal blockage of the filtration device (water recovery rate: 99. 3%).

3) In each case, the turbidity of the purified water was 0.1 or less (according to 9. Turbidity of turbidity measurement method: Industrial water test method-JISK 0101-).

Test Example 1 (Confirmation of the effect of additional cleaning)

1. Raw water

Lake Biwa was sampled 200 m offshore at a depth of 2 m and used as it was. Its turbidity was 5 and SS was 16 ppm. Most of S S was organic.

2. Test equipment

Same as Test Example 1.

3. Exam

The procedure was performed as follows.

① Back pressure washing (Water temperature: 18: Filtration pressure: 10 OkPa, Filtration flow rate: 0.6 Performed after filtration for 30 minutes at m3 / h. The conditions are the same as in Test Example 1).

(2) Backwashing (one time after performing filtration + backwashing four times, under the same conditions as Test Example 1)

③ Chemical washing (First chemical washing. Backwashing is performed twice and then once, following the procedure below) · First chemical passing process (washing water: raw water with chlorine injected, available chlorine: 5 ppm, Water passing method: Same as back washing except that the washing water is also filled in the secondary side of the hollow fiber. Water passing speed: 0.5 times the filtration operation, water passing time: 2 minutes)

• 1st holding process (holding time: 10 minutes)

• First back-pressure chemical washing process (The conditions are the same as the back-pressure washing except that the washing water filled in the secondary side of the hollow fiber during the first chemical passing process is used as the washing water.)

• First backwashing step (conditions are the same as for backwashing)

4. Test results

① No decrease in the filtration flow rate was observed at all even after about one month of operation.

(2) The filtration flow was reduced by about 7% only with the basic cleaning, but it was confirmed that the filtration flow recovered to almost the initial state by adding the first chemical cleaning.

(3) Since the constituents of SS in the raw water were mostly organic, there was no need to perform the second chemical washing. Industrial applicability

ADVANTAGE OF THE INVENTION According to this invention, it is possible to perform filtration for a long time without requiring special pretreatment, and furthermore, it is not necessary to add a chlorine-based chemical to raw water in the filtration operation, so that economical and safe water purification is possible. A manufacturing method may be provided.

Claims

The scope of the claims

1. Hollows that form a filtration layer by regularly and superimposingly winding a bundle of hollow fibers around a core tube arranged in the center of a vertical cylindrical pressure vessel so as to extend in the axial direction so as to have uniform openings. A method for producing purified water using a one-fiber ultrafiltration membrane, comprising: a filtration operation, total filtration, and raw water formed between an inner peripheral surface of the pressure vessel and an outer peripheral surface of the filtration layer. Is supplied from the outer peripheral space toward the core tube, and filtration water is extracted from the inner cavity of the hollow fiber. The washing operation of the filtration layer including the membrane surface of the hollow fiber is performed by the hollow fiber. It is characterized by being carried out by a basic washing consisting of back pressure washing in which filtered water flows from the lumen of the yarn toward the outside thereof and back washing with raw water or filtered water supplied from the core tube toward the outer peripheral space. how to.

2. The method according to claim 1, wherein a filling rate of a hollow fiber bundle constituting the filtration layer with respect to a fillable space inside the pressure vessel is at least 0.5.

3. The method according to claim 1 or 2, further comprising, after the filtration basic washing, performing an empty washing in which air is rapidly flown from the core tube toward the outer peripheral space.

4. After the above-mentioned basic washing, a first chemical washing in which raw water or filtered water containing hypochlorite ions therein flows from the core tube toward the outer peripheral space, The method according to claim 1 or 2, further comprising performing a second chemical washing in which raw water or filtered water containing an acid therein is directed from the pipe toward the outer peripheral space.

5. The first chemical washing flows the hypochlorite ion-containing raw water or filtered water from the core tube toward the outer peripheral space, and places the hypochlorite solution in the pressure vessel. A first pass-through step for introducing raw water or filtered water containing carbon dioxide, and a first retention mechanism for keeping the introduced raw water or filtered water containing hypochlorite ion for a predetermined time in the pressure vessel. And transferring the hypochlorite ion-containing raw water or filtered water moved to the filtered water side through the pores of the hollow fiber in the first drug passing step from the lumen side of the hollow fiber to the outside thereof. After flowing the first reverse pressure chemical washing step, and flowing the raw water or filtered water containing hypochlorite ion along the same route as the first chemical passing step, further feed raw water or hypochlorite ion-free water. A first backwashing step of flowing filtered water through the same route, wherein the second chemical washing is performed using the acid-containing raw water or the filter. The supercooled water flows from the core tube toward the outer peripheral space, and the water flows into the pressure vessel. A second pass-through step of introducing acid-containing raw water or filtered water, a second holding step of keeping the introduced hydrochloric-acid-containing raw water or filtered water in the pressure vessel for a predetermined time, and A second counter-pressure washing step in which the acid-containing raw water or filtered water that has been moved to the filtered water side through the pores of the hollow fiber in the drug passing step flows from the lumen side of the hollow fiber to the outside; A second backflow washing step in which the acid-containing raw water or the filtered water is caused to flow along the same route as the second chemical passing step, and further, the acid-free raw water or the filtered water is caused to flow along the same route. The method of paragraph 4 above.

6. The hypochlorous acid concentration of the hypochlorite ion-containing raw water or filtered water in the first holding step is 2 to 2 O ppm, the holding time is 2 to 20 minutes, 6. The method according to claim 5, wherein the pH of the acid-containing raw water or the filtered water in the second holding step is 2.5 to 4.0, and the holding time is 2 to 20 minutes.

7. The method according to any one of claims 1 to 6, wherein the raw water is brackish water or seawater, and the purified water obtained by the filtration operation is supplied as it is as raw water for desalination treatment by a reverse osmosis method. The method according to any one of the preceding claims.