JP2000246069A - Membrane filtration apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently separate and remove pollutants almost parted by back washing from the surfaces of filtration membranes by pushing out and washing the filtration membranes by making washing water spontaneously flow to a raw water chamber after back washing of the membranes and decreasing the inner pressure of the raw water chamber while passing the washing water through the raw water chamber. SOLUTION: This membrane filtration apparatus comprises a water storage tank 34 for washing water to store filtered water in the upper end of a membrane filtration module 14. After back washing of the membrane filtration module 14 by driving a back washing pump 40, the filtered water in the washing water storage tank 34 is made to spontaneously flow down to the raw water side of the membrane filtration module to wash out the pollutants adhering to the surfaces of the membrane filters.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane filtration apparatus having a membrane filtration module that includes a raw water chamber and a treated water chamber separated by a filtration membrane and removes suspended substances from the raw water by permeating the filtration membrane. In particular, it relates to cleaning of a filtration membrane.

[0002]

2. Description of the Related Art Conventionally, when producing raw water such as industrial water, tap water, pure water or ultrapure water using river water, lake water, dam water, industrial water, etc. as raw water, or in purifying waste water, BACKGROUND ART A membrane filtration device that performs a filtration treatment on a suspended substance using a filtration membrane having fine pores is used. This membrane filtration device includes MF (microfiltration), UF (ultrafiltration), and NF (nanofiltration) depending on the pore size of the membrane used.
Examples of the membrane shape include a hollow fiber membrane, a tubular membrane, a spiral membrane, and a flat membrane.

In such a membrane filtration device, a filtration membrane is disposed in a pressure vessel, and the inside is separated into a raw water chamber and a treated water chamber. Then, raw water is injected into the raw water chamber from the injection pump, and filtered water that has passed through the filtration membrane is obtained in the treated water chamber.

[0004] By the filtration treatment, contaminants composed of suspended substances separated by filtration accumulate on the surface of the filtration membrane, and the filtration ability is reduced. Therefore, backwashing is performed periodically to recover the filtration ability. In other words, clean water such as filtered water or tap water is pressure-fed to the treated water chamber as backwashing water, and the washing water is passed through the filtration membrane from the treated water chamber to the raw water chamber in a direction opposite to the filtration direction of the raw water. Then, the contaminants accumulated on the surface of the filtration membrane are peeled and removed.

[0005]

In a membrane filtration apparatus, this backwashing must be performed at a relatively high frequency in order to restore the performance of the filtration membrane. However, even if such backwashing is performed, pollutants are not removed. The film could not be sufficiently peeled off from the film surface, and as a result, the film was rapidly contaminated. Therefore, the film had to be washed with a chemical such as an acid or an alkali at an early stage.

[0006] The present invention has been made in view of the above problems, and has as its object to provide a membrane filtration device that can more effectively clean a filtration membrane.

[0007]

SUMMARY OF THE INVENTION The present invention provides a membrane filtration module comprising a raw water chamber and a treated water chamber separated by a filtration membrane, and having a membrane filtration module for removing suspended substances from the raw water by permeating the filtration membrane. A washing water storage tank that is provided at a position higher than the upper end of the membrane module and stores washing water, and allows the washing water in the washing water storage tank to flow under natural flow into the raw water chamber of the membrane filtration module. And a washing means for washing the filtration membrane.

[0008] In the filtration step, most of the contaminants adhering to the surface of the filtration membrane are separated from the membrane surface by backwashing, but a part of the contaminants is attached to the membrane surface in a state of being almost separated. Also exists. The contaminants that are about to peel off will re-adhere to the membrane surface when entering the filtration process again, contaminating the membrane. In the present invention, between the usual backwashing step and the filtration step, washing water is passed through the raw water chamber by natural flow using the above-mentioned washing means to wash the filtration membrane. Therefore,
The contaminants consisting of suspended substances that are coming off from the surface of the filtration membrane due to backwashing can be removed by being washed away by the flow of washing water. Thus, the filtration membrane can be effectively washed, and the filtration can be continued for a long period of time.

In the above-mentioned washing step, it is preferable not to apply pressure as much as possible in order to avoid the re-adhesion of the contaminants to the film surface, and therefore it is preferable that the washing water flow under natural flow.

Further, in the present invention, at the time of filtration, the raw water flows in the raw water chamber of the membrane filtration module in one direction, and at the time of washing, the washing water flows through the washing means in the raw water chamber in the opposite direction to that at the time of filtration. It is preferred that

[0011] Contaminants adhering to the surface of the filtration membrane tend to be scaly along the direction of flow of raw water in the filtration. Therefore, by flowing the washing water in the direction opposite to the flow direction of the raw water in the filtration, the peeling-off contaminants can be removed from the filtration membrane surface in such a manner as to peel off scales, which is very effective. Washing can be performed.

[0012]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a membrane filtration device according to an embodiment. Raw water such as river water is stored in a raw water storage tank 10. A membrane filtration module 14 is connected to the raw water storage tank 10 via a raw water pipe 12. A raw water pump 16 is provided in the raw water pipe 12, and the raw water in the raw water storage tank 10 is pressure-fed to the membrane filtration module 14 by the raw water pump 16.

The membrane filtration module 14 is installed vertically, and the lower raw water inflow chamber 18 and the membrane filtration element 22
And a raw water discharge chamber 20 at the upper part. The membrane filtration element 22 is composed of a number of internal pressure type hollow fiber membranes 22a. As shown in FIG. 2, the hollow fiber membrane separates a space inside the hollow fiber from an external space. Membrane 22
The inside of a constitutes a raw water chamber 26 connecting the raw water inflow chamber 18 and the raw water discharge chamber 20, and the outside of the hollow fiber of the hollow fiber membrane 22a forms a treated water chamber 24.

The raw water discharge chamber 20 of the membrane filtration module 14
Is connected to the suction side of the raw water pump 16 via a circulation pipe 28. Therefore, the raw water in the raw water storage tank 10 is
The raw water is supplied to the raw water inlet chamber 18 of the membrane filtration module 14 by the raw water pump 16, and is circulated from the raw water pump 16 through the raw water discharge chamber 20 through the raw water chamber 26 inside the hollow fiber of the membrane filtration element 22. Here, the membrane filtration element 2
The filtered water that has passed through the filtration membrane from inside the hollow fiber of No. 2 reaches the treated water chamber 24.

A treated water pipe 32 is connected to the treated water chamber 24. The treated water pipe 32 is connected to a treated water storage tank 36 via a cleaning water storage tank 34. Then, the filtered water obtained by the membrane filtration module 14 is introduced into the treated water storage tank 36 via the cleaning water storage tank 34. The treated water in the treated water storage tank 36 is discharged out of the system and supplied to, for example, a subsequent pure water production facility or the like.

The treated water storage tank 36 has a backwash pipe 38.
The backwash pipe 38 is connected to a backwash pump 40.
Is connected to the treated water pipe 32 via the. Then, by driving the backwash pump 40, the treated water in the treated water storage tank 36 is pumped to the treated water chamber 24 of the membrane filtration module, and the membrane filtration element 22 can be backwashed.
Wash water drain pipes 42 and 44 are connected to the raw water inflow chamber 18 and the raw water discharge chamber 20, and backwash drain water is discharged therefrom.

In the present embodiment, the cleaning water storage tank 34 is disposed at a position higher than the upper end of the membrane filtration module 14, and the cleaning water storage tank 34 and the raw water discharge chamber 20 of the membrane filtration module 14 It is connected by a water pipe 46. Therefore, the filtered water in the cleaning water storage tank 34 can be supplied to the raw water discharge chamber 20 under natural flow, and can be drained from the cleaning drainage pipe 44. As a result, the treated water in the washing water storage tank 34 flows into the raw water chamber 26 of the membrane filtration element 22 under natural flow.

In the above description, the valve is omitted, but a valve is appropriately provided in each pipe, and a flow path can be appropriately selected by opening and closing the valve.

Next, the processing operation will be described with reference to FIG. In the filtration step, the raw water pump 16 is driven to convert the raw water into the raw water inflow chamber 1 below the membrane filtration module 14.
To 8 Thus, the raw water flows through the membrane filtration module 14 into the raw water inflow chamber 18, the raw water chamber 26 inside the hollow fiber,
The raw water is circulated to the suction side of the raw water pump 16 through the circulation pipe 28 in the order of the raw water discharge chamber 20. Therefore, in the raw water chamber 26, the raw water flows in an upward flow. Then, part of the raw water in the raw water chamber 26 passes through the hollow fiber membrane 22 a of the membrane filtration element 22 and reaches the treated water chamber 24. At this time, the suspended matter in the raw water is separated by the hollow fiber membrane 22a of the membrane filtration element 22, and accumulated on the surface of the raw water chamber 26 side. Therefore, by the continuation of the filtration process, contaminants composed of suspended substances are gradually accumulated on the surface of the membrane filtration element 22 on the raw water chamber 26 side.

As a result, the filtration capacity of the membrane filtration module 14 decreases, and a sufficient amount of treated water cannot be obtained. Therefore, a backwashing step is periodically performed. That is, the driving of the raw water pump 16 is stopped, the backwash pump 40 is driven,
The filtered water in the treated water storage tank 36 is pumped into the treated water chamber 24. Thereby, the filtration treatment water flows through the membrane filtration element 22 from the treatment water chamber 24 side to the raw water chamber 26 side,
Backwashing is performed to remove and remove contaminants accumulated on the surface of the membrane filtration element 22 on the raw water chamber 26 side.

After this back washing step, an extrusion washing step is carried out using the filtered water in the washing water storage tank 34. In this extrusion cleaning step, the backwash pump 40 is stopped, and the filtered water in the cleaning water storage tank 34 is allowed to flow naturally into the raw water chamber 26 of the membrane filtration module, that is, into the internal space of the hollow fiber membrane 22a. As a result, FIG.
As shown in (1), contaminants remaining on the surface of the membrane filtration element 22 on the side of the raw water chamber 26 inside the hollow fiber are peeled and removed. In particular, in the extrusion cleaning step, the flow of the filtered water in the raw water chamber 26 is a downward flow, and is in the opposite direction to the flow of the raw water in the water passing step. Therefore, the separation of the contaminants attached to the surface of the membrane filtration element 22 is promoted.

In particular, the contaminants adhering to the surface of the membrane filtration element 22 tend to be scaly along the direction of the flow of raw water in the filtration step, as shown in FIG. Therefore, immediately after the backwashing step, when the filtration step is started, the contaminants are pressed against the filtration membrane surface again, and the contaminants adhere. By providing an extrusion cleaning step in which the water flow direction is reversed between the backwashing step and the filtration step, contaminants that have started to peel off can be removed from the filtration membrane surface as if the scales were peeled off. The effect can be obtained.

The extrusion cleaning step does not need to be performed after each backwashing, and may be performed according to the properties of raw water.
It may be carried out once a day to about once a week, after ordinary backwashing.

Further, in the present embodiment, in the extrusion cleaning step, the filtered water in the backwash water storage tank 34 flows down into the raw water chamber 26 under natural flow. According to such a natural flow, the pressure in the raw water chamber 26 at that time can be considerably reduced as compared with the case where the water is pumped. Therefore, the pressing force on the film surface is low, and the attached contaminants can be effectively removed.

Further, since the flow is caused by natural flow, a rotating device such as a pump is unnecessary. In addition, the washing water storage tank 34 installed at a position higher than the upper end of the membrane filtration module 14 is sufficient for the volume of the raw water side chamber (the raw water inflow chamber 18, the raw water chamber 26, and the raw water discharge chamber 20) of the membrane module 14. It is. Further, one washing water storage tank 34 may be provided for one membrane filtration system. However, since the timing of the extrusion cleaning process can be different, only one tank is provided for a plurality of membrane filtration systems. Is also good.

Here, the washing water used in the extrusion washing step is not limited to the filtered water, but may be activated carbon treated water (when there is an activated carbon treatment device at the subsequent stage), tap water, or the like. Further, the cleaning water is preferably as clean as possible, but raw water can also be used. Further, the membrane filtration module is not limited to the internal pressure type hollow fiber, and various types can be used. In particular, a tubular type membrane such as a hollow fiber membrane or a tubular membrane is suitable. Further, the filtration method is not limited to the cross-flow filtration as described above, and may be a total amount filtration.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Using an apparatus having the same configuration as that shown in FIG.
Processing experiments were performed on a conventional example in which only normal backwashing without the extrusion cleaning step was performed, and on an apparatus of the present invention in which the extrusion cleaning step was provided after the backwashing step. The membrane module used is an internal pressure type hollow fiber membrane module. Table 1 shows the conditions at that time. Thus, in the present invention, the extrusion cleaning step is performed once a week (once for every 220 times of backwashing).
The same conditions were followed, except that it was performed after a normal backwashing step.

[0029]

[Table 1] The change in the transmembrane pressure (differential pressure between the raw water chamber 26 side and the treated water chamber 24 side of the membrane filtration element 22 for obtaining constant filtration water) in the conventional example and the present invention in the result of this experiment is shown. As shown in FIG. Thus, in the conventional method, in two months of operation,
The transmembrane pressure increased and chemical cleaning was required. On the other hand, in the present invention, chemical cleaning was required for 7 months of operation.

From the above, it is understood that the apparatus of the present invention can effectively perform membrane cleaning and greatly extend the stable operation period.

[0031]

As described above, in the present invention, after performing the normal backwashing, the washing water is flowed to the raw water chamber by natural flow to extrude and wash the filtration membrane. For this reason, the pressure in the raw water chamber can be reduced, and the cleaning water can be circulated in the raw water chamber, whereby the contaminants on the surface of the filtration membrane that are about to be separated by the backwash can be effectively separated and removed. . As a result, the filtration membrane can be effectively cleaned,
Filtration can be continued for a long time.

In addition, by performing the extrusion cleaning in which the direction of water flow is the reverse of the direction of filtration, the contaminants that have come off in the backwash can be removed from the surface of the filtration membrane by peeling off the scales. A good cleaning effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a membrane filtration device according to an embodiment of the present invention.

FIG. 2 is a view showing a configuration of an internal pressure type hollow fiber membrane.

FIG. 3 is a diagram showing a state of a contaminant in each step.

FIG. 4 is a diagram showing a change in transmembrane pressure due to continuation of operation.

[Description of Signs] 10 raw water storage tank, 14 membrane filtration module, 16 raw water pump, 18 raw water inflow chamber, 20 raw water discharge chamber, 22
Membrane filtration element, 24 treated water chamber, 26 raw water chamber, 3
4 Washing water storage tank, 40 backwash pump.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akiaki Masaki 1-2-8 Shinsuna, Koto-ku, Tokyo Organo Corporation F-term (reference) 4D006 GA05 GA06 GA07 HA02 HA18 HA22 JA58A JA67A KA63 KC02 KC03 KC05 KC13 KE04P KE05Q KE06P KE22Q KE23Q KE24Q KE28Q MA01 MA02 PA01 PB02 PB04 PB08 PC03

Claims (2)

[Claims] 1. A membrane filtration device comprising a raw water chamber and a treated water chamber separated by a filtration membrane, wherein the membrane filtration module has a membrane filtration module for removing suspended substances from raw water by permeating the filtration membrane. A washing water storage tank provided at a position higher than the upper end for storing washing water, and washing water in the washing water storage tank flowing under natural flow into the raw water chamber of the membrane filtration module to wash the filtration membrane. Means, and a membrane filtration device comprising: 2. The apparatus according to claim 1, wherein at the time of filtration, the raw water flows in one direction into the raw water chamber of the membrane filtration module, and at the time of cleaning, the washing means is used to reverse the cleaning water into the raw water chamber. A membrane filtration device characterized by flowing in the direction.