JP2002126468A - Membrane module cleaning method and membrane filtration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane module cleaning method and a membrane filtration device capable of performing effective membrane cleaning only by using a small amount of air without lowering a water recovery rate. SOLUTION: In a state where water is present on the raw water side, the membrane module is washed by blowing air from the permeation side of the membrane toward the raw water side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a membrane module and a membrane filtration apparatus, and more particularly, to a membrane module in a membrane filtration apparatus used as a solid-liquid separation means for a water treatment facility for tap water, sewage and the like. And a configuration of a membrane filtration device for performing the cleaning method.

[0002]

2. Description of the Related Art Membrane filtration devices, which have been rapidly commercialized in recent years as solid-liquid separation means in various water treatments, have the advantage that solid-liquid separation can be reliably performed with a simple and compact device configuration. However, in order to prevent clogging, the membrane module used in the membrane filtration device needs to be washed every predetermined period, and conventionally, a part of the membrane filtration water is flowed in the opposite direction from the permeation side of the membrane. Physical cleaning methods such as flowing back washing and air scrubbing for diffusing air from below the membrane module are performed in an appropriate combination.

[0003]

However, in backwashing, a part of membrane filtration water is used to remove dirt on the membrane surface, and therefore, there is a problem that the water recovery rate is reduced.
Air scrubbing has a problem that the amount of diffused air must be increased in order to obtain an air scrubbing effect over the entire membrane surface.

Accordingly, an object of the present invention is to provide a membrane module cleaning method and a membrane filtration device which can perform effective membrane cleaning by using only a small amount of air without lowering the water recovery rate. And

[0005]

In order to achieve the above object, a method for cleaning a membrane module according to the present invention comprises the steps of:
It is characterized in that air is ejected in a state where water is present on the raw water side.

[0006] In the membrane filtration device of the present invention, an air supply path provided with an air compressor for supplying compressed air to a permeation side of the membrane is provided in the membrane filtration device for performing a filtration treatment by a membrane module. In addition, an air supply path for introducing air is provided on the permeation side of the membrane, and a vacuum pump for reducing the pressure on the raw water side of the membrane is provided.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram showing a first embodiment of a membrane filtration apparatus which enables the method for cleaning a membrane module of the present invention. This membrane filtration device is a so-called internal pressure circulation type membrane treatment device that performs a filtration operation by supplying raw water to the inside of a hollow fiber membrane forming a membrane module, and converts raw water in a raw water tank 11 into an internal pressure type. A raw water pump 13 for supplying the separation unit provided with the membrane module 12, a circulation pump 14 for pressurizing the raw water and circulating the raw water to the membrane module 12,
A circulation path 15 for circulating the raw water flowing out from the membrane module 12 to an upstream side of the circulation pump 14, a membrane filtration water outlet pipe 16 for taking out the membrane filtration water, and a pair of an air washing switching valve 17a connected to the membrane filtration water outlet pipe 16; , 17b, and an air compressor 19 for supplying compressed air to the air supply path 18, and a backwash wastewater for returning the backwash wastewater to the raw water tank 11 and a water treatment apparatus in the preceding stage. A return path 20 and a pair of backwash switching valves 21a and 21b for switching the path of the membrane module effluent are provided.

[0008] In the filtration process, the raw water pump 13 and the circulation pump 14 are operated, and the empty washing switching valve 17a and the back washing switching valve 21 are operated.
a is opened, and the empty washing switching valve 17b and the backwashing switching valve 21b are closed. The raw water supplied from the raw water tank 11 by the raw water pump 13 is pressurized by the circulation pump 14 together with the circulating water from the circulation path 15 and is supplied to the membrane module 12.
Is supplied to the hollow fiber membrane raw water side (inside side). The membrane filtered water that has passed through the hollow fiber membrane from the inside to the outside is taken out from the membrane filtered water outlet pipe 16, passes through the flush switch valve 17 a, is discharged to a river or the like, or is sent to a post-treatment facility. On the other hand, the raw water that has passed through the inside of the hollow fiber membrane as it is
It circulates from the circulation path 15 to the upstream side of the circulation pump 14 through 1a. As a result, membrane filtered water corresponding to the supply amount from the raw water pump 13 is obtained, and the raw water subjected to a predetermined pretreatment flows into the raw water tank 11 from the inflow path 22.

In such an internal pressure circulation type membrane treatment apparatus, it is necessary to periodically perform a backwashing treatment for removing dirt adhering to the raw water side (inner side) of the hollow fiber membrane. Wash switching valves 17a, 17b and backwash switching valves 21a, 21b
To open and close the air-washing changeover valve 17b and the backwash changeover valve 21b.
Is opened, the empty washing switching valve 17a and the back washing switching valve 21a are closed, and the air compressor 19 is operated to supply compressed air to the permeation side (external side) of the hollow fiber membrane.
At this time, a state in which raw water exists on the raw water side of the membrane module 12, that is, a state in which a small amount of water flows through the raw water pump 13 and the circulation pump 14, or
The raw water is caused to flow by the buoyancy of the air transmitted to the raw water.

As a result, as shown in FIG.
The air A that permeates from the outer side to the inner side of the hollow fiber membrane 23 is jetted out as bubbles B into water (raw water) W existing on the inner side, flows through the membrane together with the water flow, and flows through the membrane module 12.
And flows back through the backwash drain return path 20 through the backwash switching valve 21b. At this time, dirt on the entire membrane surface can be effectively removed by the air scrubbing effect of air bubbles B of the air that has passed through the hollow fiber membrane 23, and the membrane module 12 can be backwashed without using membrane filtration water. Water recovery rate can be increased. The supply pressure of the compressed air varies depending on conditions such as the type of the hollow fiber membrane 23 used in the membrane module 12 and the pressure of the backwash drainage water return path 20, but is usually 50 to 100 kPa.
(Gauge pressure).

FIG. 3 is a system diagram showing a second embodiment of the apparatus of the present invention. In the following description, the same components as those of the first embodiment will be denoted by the same reference numerals, and detailed description will be omitted.

In the apparatus of this embodiment, the supply of backwash air to the membrane module 12 is performed by the air supply path 1 in the above embodiment.
8 instead of the air compressor 19 provided in the
This is performed by suctioning with a vacuum pump 31 provided at zero, and backwashing of the membrane module 12 can be performed by using a part of the membrane filtered water as backwash water.

In other words, the air supply path 18 is not provided with the air compressor 19, but is opened to the atmosphere, and the raw water side of the module 12 is vacuum-sucked by the vacuum pump 31 provided in the backwashing drain return path 20. Atmospheric air sucked from the air supply path 18 is transmitted from the outside of the membrane of the membrane module 12 to the inside of the membrane. At the inlet of the membrane module 12, a shut-off valve 32 for preventing the suction of raw water during vacuum suction is provided.

Further, in order to perform backwashing with the membrane filtered water, a backwash water supply path 35 having a flush valve 33 and a backwash water pump 34 is provided in the membrane filtered water outlet pipe 16, and the membrane module 12 is provided with: A drain valve 37 is provided for discharging the backwash wastewater permeated from the outside of the hollow fiber membrane to the inside of the membrane, or the second backwash wastewater return path 36 for returning the backwash wastewater to the preceding water treatment apparatus.
Is provided via

In the above water backwash, the hollow fiber membrane 23 is washed with backwash water.
Not only for cleaning but also for supplying air into the membrane module 12 to obtain an air scrubbing effect by air bubbles at the time of air backwashing. Therefore, in this embodiment, air backwashing and water backwashing are performed alternately.

Since the backwashing operation is started in a state where raw water and membrane filtered water remain in the membrane module 12, either air backwashing or water backwashing may be performed first. When performing air backwashing, the air washing switching valve 17a, which was opened during the filtration operation,
This is performed by closing the backwashing switching valve 21a and the shutoff valve 32, and opening the empty washing switching valve 17b and the backwashing switching valve 21b, respectively, and operating the vacuum pump 31. As a result, as shown in FIG. 2, the atmospheric air A sucked from the air supply path 18 passes through the hollow fiber membrane 23 to become bubbles B, and after cleaning the raw water side (inside side) of the membrane module 12. Backwash switching valve 2 with water inside the membrane
1b is sucked by the vacuum pump 31 and returned through the backwash drainage return water path 20.

When switching from this state to water backwashing, the flushing switching valve 17b and the backwashing switching valve 21b are closed and the flushing valve 3 is closed.
3 and the drain valve 37 are opened, and the backwash water pump 34 is operated. As a result, a part of the membrane filtered water is pumped to the permeate side of the membrane module 12 by the backwash water pump 34, and the backwash wastewater after the water backwash is discharged and returned through the second backwash wastewater return path 36. .

Switching between air backwashing and water backwashing may be performed according to the degree of water present in the membrane module 12, and can be appropriately set according to conditions such as the volume of the membrane module 12. By alternately performing the air backwashing and the water backwashing in this manner, the air backwashing can be performed in a state where water is present on the raw water side of the membrane module 12, so that the same air scrubbing effect as described above allows the entire membrane surface to be washed. Dirt can be effectively removed. The supply of water to the raw water side can also be performed by slightly opening the shut-off valve 32 and sucking the raw water by the vacuum pump 31 at the time of air backwashing. In addition, the empty washing switching valves 17a and 17b and the back washing switching valve 21
Each of a and 21b can be replaced with one three-way switching valve.

FIG. 4 shows a third embodiment of the present invention.
FIG. 2 is a system diagram showing an example in which the present invention is applied to an external-pressure total-filtration type membrane treatment apparatus that performs a filtration operation by supplying raw water to the outside of a hollow fiber membrane. The membrane filtration device includes an external pressure type membrane module 42 immersed in a filtration tank 41, a suction pump 44 for sucking membrane filtration water of the membrane module 42 through a membrane filtration water outlet pipe 43, and a raw water tank 11. A raw water pump 46 for supplying the raw water to the filtration tank 41 via a raw water supply pipe 45, an air supply path 18 connected to the membrane filtration water outlet pipe 43 via a pair of air washing switching valves 17a and 17b, and the air supply An air compressor 19 for supplying compressed air to the passage 18 and a drain passage 47 and a drain valve 48 for discharging the concentrated water in the filtration tank 41 are formed. When the filtration tank 41 is a closed type, a backwash drain return path 50 having a return valve 49 is provided.

The ordinary filtration process is performed by operating the suction pump 44 and the raw water pump 46 with the empty washing switching valve 17a opened, the empty washing switching valve 17b and the drain valve 48 closed. That is, the inside of the hollow fiber membrane of the membrane module 42 is sucked by the suction pump 44 to be in a reduced pressure state,
By relatively increasing the pressure on the outer side of the hollow fiber membrane, the water in the filtration tank 41 is permeated from the outer side to the inner side of the hollow fiber membrane to perform a filtration treatment.

In such an external pressure type air backwash, the raw water pump 46 is stopped, and the air flush
The air compressor 19 is opened and closed by switching the open / close state of the air-cleaning switching valve 17b and closing the air-cleaning switching valve 17a.
Is operated to supply compressed air to the permeation side (inside) of the hollow fiber membrane. At this time, since raw water is present in the filtration tank 41 outside the membrane module 42, as shown in the explanatory view of FIG.
The air A supplied to the inner side of 3 is blown out as bubbles B into the raw water W on the outer side, and floats on the water surface by buoyancy.

The air floating on the surface of the water is
In the case of the open type, the gas is discharged from the upper opening, and in the case of the closed type, the return valve 49 is opened to open the backwash drain return path 5.
Returned from 0 to the appropriate location. Further, in the case of the apparatus having the backwash drainage return path 50, the air backwash can be performed while the raw water pump 46 is operated.

Therefore, in the case of the external pressure type as well, similarly to the internal pressure type, dirt on the entire membrane surface can be effectively removed by the air scrubbing effect of the bubbles ejected to the raw water side, and at the same time, the water recovery rate can be increased. it can. At the end of the air backwashing, the drainage valve 48 is opened to discharge the washing wastewater in the filtration tank 41 from the drainage passage 48. In addition, the drainage valve 48 is opened / closed according to the situation in the filtration tank 41 during the filtration processing, and by appropriately discharging the concentrated water in the filtration tank 41, it is possible to prevent a reduction in the filtration processing efficiency.

Further, as shown by an imaginary line in FIG. 4, an air diffuser 52 connected to a blower 51 is provided at the bottom of the filtration tank 41 to perform air diffusion at an appropriate time, so that the air scrubbing effect is obtained. During the filtration process, the membrane module 42
In addition to suppressing the adhesion of suspended matter to the air, the backwash effect at the time of air backwash can be further enhanced. In addition, in this embodiment, it is also possible to use water backwashing in which a part of the membrane filtered water is backwash water.

[0025]

As described above, according to the present invention,
The air scrubbing effect of air bubbles transmitted from the permeation side of the membrane toward the raw water side can effectively remove dirt on the entire membrane surface, and backwash the membrane module without using membrane filtration water. Water recovery rate can be increased.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a first embodiment in which the present invention is applied to an internal pressure circulation type membrane processing apparatus.

FIG. 2 is an explanatory view showing an air backwashing state of a hollow fiber membrane in an internal pressure circulation system.

FIG. 3 is a system diagram showing a second embodiment in which the present invention is applied to an internal pressure circulation type membrane processing apparatus.

FIG. 4 is a system diagram showing an embodiment in which the present invention is applied to an external pressure total filtration membrane treatment apparatus.

FIG. 5 is an explanatory diagram showing an air backwash state of a hollow fiber membrane in an external pressure type.

[Explanation of symbols]

11: Raw water tank, 12: Membrane module, 13: Raw water pump, 14: Circulation pump, 15: Circulation path, 16: Membrane filtered water outlet pipe, 17a, 17b: Empty washing switching valve, 18: Air supply path, 19 ... Air compressor, 20 ... Backwash drainage return path,
21a, 21b ... backwash switching valve, 22 ... inflow path, 23 ...
Hollow fiber membrane, 31: vacuum pump, 32: shut-off valve, 33: flush valve, 34: backwash water pump, 35: backwash water supply path, 3
6: second backwash drain return path, 37: drain valve, 41: filtration tank, 42: membrane module, 43: membrane filtered water outlet pipe, 44
... Suction pump, 45 ... raw water supply pipe, 46 ... raw water pump,
47: drainage path, 48: drain valve, 49: return valve, 50:
Backwash wastewater return path, 51: blower, 52: air diffuser

Claims (3)

[Claims] 1. A method for cleaning a membrane module, comprising: blowing air from the permeation side of the membrane to the raw water side in a state where water is present on the raw water side when cleaning the membrane module. 2. A membrane filtration device for performing a filtration treatment by a membrane module, wherein an air supply path provided with an air compressor for supplying compressed air to a permeation side of the membrane is provided. 3. A membrane filtration device for performing a filtration treatment by a membrane module, wherein an air supply path for introducing air to the permeation side of the membrane is provided, and a vacuum pump for reducing the pressure of the raw water side of the membrane is provided. And a membrane filtration device.