JP2002361054A - Method for washing membrane filtration apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for washing a membrane filtration apparatus, by which stable membrane filtration can be continued for a long period of time without clogging a separation membrane of the membrane filtration apparatus over a long period of time. SOLUTION: This method for washing the membrane filtration apparatus comprises the operation of washing the separation membrane under back pressure by supplying any or both of acid water and alkaline water manufactured by electrolyzing water to the filtrate side 12b of a membrane filtration unit 12 and the operation of blowing the air containing ozone toward the side 12a of the water to be treated of the unit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for cleaning a separation membrane in a membrane filtration device provided with a separation membrane such as a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, and a reverse osmosis membrane.

[0002]

2. Description of the Related Art In recent years, with the development of membrane separation technology, membrane filtration has been performed in water treatment fields such as water purification of waterworks, treatment of industrial wastewater, and sewage treatment. For example, in water purification treatment of water supply, a process of filtering surface water of river water or lake water using a microfiltration membrane or an ultrafiltration membrane made of a hollow fiber membrane, a flat membrane, or the like is performed. In the membrane filtration of this water purification treatment, the same or higher turbidity performance can be obtained as in the case of the conventional two-stage purification treatment by coagulation sedimentation and sand filtration. It is compact and the configuration is simplified.

By the way, if the filtration by the separation membrane is continued, pollutants adhere to the surface of the membrane or in the pores of the membrane and the membrane is clogged, and the permeation resistance of the separation membrane gradually increases.
In order to recover the filtration performance reduced by fouling, the apparatus is stopped at predetermined time intervals and the separation membrane is washed. The method of washing the membrane performed at this time includes back pressure water washing in which the membrane filtered water flows in the direction opposite to the filtration direction from the filtrate water side (secondary side) of the separation membrane and flows backward, and the separation membrane using raw water Of the water to be treated (primary side), and back pressure air washing by blowing pressurized air from the secondary side of the separation membrane. For example, in the water purification treatment of waterworks, the separation membrane cleaning is generally performed at a frequency of about once every 10 to 120 minutes of operation time.

[0004] Even if the separation membrane is washed as described above, substances that cannot be removed gradually adhere to the separation membrane, and if filtration is continued for a long time, the permeation resistance of the separation membrane causes the membrane filtration device to fail. It increases to the extent that it cannot be operated efficiently. For this reason, cleaning is performed in which substances that could not be removed by the above-described cleaning method are removed by decomposing or dissolving using chemicals. As a cleaning chemical, caustic soda, sodium hypochlorite, etc. are used when removing organic substances, and hydrochloric acid, sulfuric acid, oxalic acid, citric acid, etc. are used when removing inorganic substances. .

In this chemical cleaning, a selected chemical is adjusted to a predetermined concentration, and this cleaning liquid is supplied to a membrane filtration device and circulated for a long time. Alternatively, after the supplied cleaning liquid is filled in the membrane filtration device, the supply of the cleaning liquid is stopped, and long-time stationary cleaning is performed. The frequency of chemical cleaning varies depending on the water to be treated, but in water purification treatment of waterworks, it is performed about once every several months.

However, when chemical cleaning is performed, after cleaning, post-treatment of rinsing using membrane filtered water or water to be treated must be performed in order to remove chemicals remaining in the apparatus. In addition, equipment must be provided to treat the cleaning wastewater containing chemicals.

[0007] In response to the above problems, Japanese Patent Laid-Open No.
No. 48423 discloses that when a separation membrane is clogged, electrolyzed water (acidic water or alkaline water) produced by a diaphragm type electrolysis device is supplied to a membrane filtration device in place of a cleaning chemical such as hydrochloric acid or caustic soda. There has been proposed a method of cleaning the separation membrane by supplying it into a passage.

[0008]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. 7-1
In the technique described in Japanese Patent No. 48423, the problem in performing the chemical cleaning is solved, but when the separation membrane is clogged, the membrane filtration device is operated for a long time as in the case of the chemical cleaning. The process must be stopped and the separation membrane washed. For this reason, the operation rate of the membrane filtration device decreases.

The present invention solves the above-mentioned problems, and provides a method for cleaning a membrane filtration device which does not cause clogging of a separation membrane for a long period of time and can continue stable membrane filtration for a long period of time. The purpose is to:

[0010]

According to a first aspect of the present invention, there is provided a method for cleaning a membrane filtration device, comprising the steps of: performing an electrolytic treatment on water; It is characterized by performing an operation of supplying one or both to the filtrate water side of the membrane filtration unit to wash the separation membrane with counter pressure water, and an operation of blowing air containing ozone into the treated water side of the membrane filtration unit.

[0011] The method for cleaning a membrane filtration device according to the second aspect of the present invention is the method according to the first aspect, wherein the separation membrane is subjected to backwashing with acidic water and backpressure of the separation membrane with alkaline water. It is characterized in that the operation of washing with water and the operation of blowing air containing ozone into the water to be treated of the membrane filtration unit are performed according to a predetermined order and time interval.

In the present invention, in order to keep the separation membrane clean for a long period of time, the reverse frequency with electrolytic water (acidic water or alkaline water) is used at the same frequency as in the case of performing normal back pressure water washing. Perform pressure water washing. Acidic water also has oxidizing power,
Alkaline water also has reducing power, so backwashing with these electrolyzed waters will remove scales and slime that could not be removed by conventional backwashing with filtered water.
Removed each time backwash water is used. For this reason, clogging of the separation membrane does not occur, and the operation of the membrane filtration device can be continued for a long period of time.

Further, since the operation of blowing air containing ozone having a strong oxidizing power into the water to be treated is also used, fouling substances which have not been removed by the back pressure water washing by the above method are also removed, and the separation membrane is removed. It is kept in a cleaner state.

[0014]

FIG. 1 is an explanatory diagram of an example according to an embodiment of the present invention. The membrane filtration device shown in FIG. 1 is a cross-flow type device used in water purification treatment of waterworks,
0 is a raw water supply tank for receiving and storing raw water (water to be treated) such as river water or lake water, 11 is a raw water supply pump, 12 is a membrane filtration unit, and 14 is a temporary storage of filtered water filtered by the membrane filtration unit. It is a membrane filtration tank for performing.

The equipment described below is an equipment for washing the separation membrane of the membrane filtration unit, 20 is an ozone generator, 21 is for extracting membrane filtration water for washing the separation membrane of the membrane filtration unit. Filtration water extraction pump, 22 is a diaphragm type electrolyzer for electrolyzing water to produce acidic water and alkaline water, 23 is an acidic water tank for temporarily storing the acid water produced by the diaphragm type electrolyzer, and 24 is alkaline water for temporary use. The stored alkaline water tank 27 is a washing and draining tank that receives washing and drainage when the separation membrane is washed with back pressure water. 28, 29, 3
Reference numerals 0 and 31 are automatic on-off valves.

The operation of this membrane filtration device is performed as follows. The raw water in the raw water supply tank 10 is supplied by the raw water supply pump 12 to the treated water side 12a of the membrane filtration unit. A circulation line 13 is provided between the treated water side 12a of the membrane filtration unit and the raw water supply tank 10, and the supplied raw water circulates between the treated water side 12a of the membrane filtration unit and the raw water supply tank 10. While being filtered. The membrane filtered water that has passed through the separation membrane is sent to the membrane filtered water tank 14 and discharged as treated water.

After performing the above-mentioned filtration operation, the separation membrane is washed at predetermined time intervals (usually, approximately once every 10 to 120 minutes). In washing the separation membrane,
First, back pressure water cleaning is performed, and then air containing ozone is blown to perform bubbling.

At the time of back pressure water washing of the separation membrane, the type of washing water is selected depending on the properties of the substance adhering to the separation membrane. For this reason, the case of supplying either the acidic water or the alkaline water produced by the diaphragm type electrolysis device 22 to perform the back-pressure water washing, and the back-pressure water washing with the acid water and the back-pressure water washing with the alkaline water alternately. May be implemented. Further, in the back pressure water washing using two kinds of acid water and alkaline water, the back pressure washing with acid water and the alkaline water is alternately supplied during one back pressure water washing. After performing, there is a case where alkaline water is used in the next back-pressure water washing.

The separation membrane is washed as follows. After stopping the membrane filtration device, first, the membrane filtration water discharged to the membrane filtration water tank 14 is extracted by the pump 21 and the membrane-type electrolysis device 2 is removed.
Introduce to 2. In this diaphragm type electrolysis device 22, the anode chamber 2
The acidic water is produced in 2a, and the alkaline water is produced in the cathode chamber 22b. The acidic water and the alkaline water produced by the diaphragm type electrolysis device 22 are stored in an acidic water tank 23 and an alkaline water tank 24, respectively. Then, for example, in the case of performing back pressure water washing for introducing acidic water first,
After activating 5, the valve 28 is opened and the valve 29 is closed, and the acidic water is supplied to the filtrate side 12b of the membrane filtration unit to wash the separation membrane with the counter-pressure water. The washing drainage is discharged to the washing drainage tank 27.

At this time, the alkaline water pump 26 is also activated to discharge the alkaline water to the washing / draining tank 27 and to join with the acidic washing / draining water. For this reason, the washing wastewater is neutralized, and its liquid property returns to the same state as the original membrane filtered water.

The pH of acidic water or alkaline water supplied for back pressure water washing of the separation membrane varies depending on the type of separation membrane to be washed, and the type of scale or slime. The pH of the alkaline water is a value within the range of 9-11. At the time of washing the separation membrane, the diaphragm type electrolysis apparatus
2. Adjust the value of the current flowing through 2.

Next, an operation of blowing air containing ozone is performed. After the above-described back-pressure water cleaning is performed for a short time of, for example, about 1 minute, air is introduced into the ozone generator 20 to generate air containing ozone, and the air containing ozone is subjected to processing by the membrane filtration unit. Bubble by blowing into the water side 12a. When air containing ozone is blown, fouling substances such as organic substances are decomposed and depolymerized by the strong oxidizing power of ozone, so that fouling substances that could not be removed by back pressure water washing can be decomposed and removed. . Further, if the above-described bubbling is performed after the back-pressure water cleaning, the separation membrane is swung, so that the fouling substance is separated and removed by the action of the bubbling itself, and the oxidizing action of ozone and the back-pressure water are performed. The adhesion layer of the fouling substance, whose adhesion has been weakened by the cleaning, is peeled off and removed.

The operation of blowing air containing ozone is not performed every time the back-pressure water is washed, but is carried out after performing the back-pressure water several times. The blowing of the ozone-containing air is performed at a frequency of about once every 6 to 48 hours, depending on the operating conditions.

In the above embodiment, the method of cleaning the membrane filtration device in the water purification treatment of the water supply has been described.
The present invention is not limited to the cleaning of a membrane filtration device for water purification treatment, but a membrane filtration device for industrial wastewater, a membrane filtration device for sewage treatment, or a membrane filtration device for desalination treatment with a reverse osmosis membrane. It can also be applied to devices.

The type of the separation membrane provided in the membrane filtration device is not particularly limited, either, and may be used for cleaning separation membranes such as microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. Can be applied. Specifically, a microfiltration membrane having a nominal pore size of 0.01 to 0.5 μm, and an ultrafiltration membrane having a molecular weight cutoff of 1,000 to 200,000 daltons are used for washing a membrane filtration device. Can be applied to

If the type of the membrane filtration unit is a casing type of a pressurized type, the shape of the membrane is hollow fiber,
The shape may be a spiral shape, a tubular shape, or a flat film shape.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A membrane filtration device having the same configuration as that of FIG.
A process of filtering surface water of river water (average turbidity of 15 degrees) was performed. The separation membrane provided in this membrane filtration device is a hollow fiber ultrafiltration membrane (made of polyacrylonitrile) having a molecular weight cut off of 130.
00 Dalton. The conditions for membrane filtration and washing were as follows. And the washing | cleaning pattern of a separation membrane performed alternate-pressure water washing | cleaning by an acidic water and alkaline water alternately, and performed bubbling with ozone-containing air after back-pressure water washing once every 36 times of back-pressure water washing. .

Membrane filtration and washing conditions Differential pressure between membranes: 70 kPa Washing interval and frequency Filtration time: 20 minutes Back pressure water washing: 60 seconds Bubbling: 60 seconds Washing water pH Acidic water pH: 4 Alkaline water pH: 10 Fig. 2 shows the change over time of the membrane permeation flux during operation depending on the conditions.
The curve a was as shown in FIG. In addition, the time-dependent change of the membrane permeation flux when only the back pressure water washing with the membrane filtration water was performed by the conventional method was as shown by the curve b.

According to the results shown in FIG. 2, when the washing was carried out by the conventional method using only the membrane filtered water (curve b), 40 times was obtained.
In daily operation, the membrane permeation flux has fallen to less than half of the initial value. For this reason, clogging of the separation membrane has reached a stage where the apparatus must be stopped and long-time cleaning with a chemical or the like must be performed.

On the other hand, when the cleaning by the method of the present invention was performed (curve a), even after the operation for 40 days,
The membrane permeation flux is only slightly reduced, and the operation can be continued for a longer period.

[0031]

According to the present invention, an operation of supplying acidic water and alkaline water obtained by passing water through a diaphragm type electrolysis apparatus to the filtrate water side of a membrane filtration unit to wash the separation membrane with back pressure water. Then, air containing ozone is blown into the water-to-be-treated side of the membrane filtration unit, so that scales and slime that could not be removed by conventional backwashing with filtered water or air bubbling are removed.

Therefore, even if the membrane filtration device is not washed with a chemical or the like which must be stopped for a long time, clogging of the separation membrane does not occur and the operation of the membrane filtration device is continued for a long time. Can be.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an example according to an embodiment of the present invention.

FIG. 2 is a diagram showing a change over time of a membrane permeation flux when the method of the present invention is performed and when a conventional method is performed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Raw water supply tank 11 Raw water supply pump 12 Membrane filtration unit 12a Treated water side of membrane filtration unit 12b Filtration water side of membrane filtration unit 13 Circulation line 14 Membrane filtration water tank 20 Ozone generator 21 Filtration water extraction pump 22 Diaphragm type electrolyzer 22a anode compartment 22b cathode compartment 23 acidic water tank 24 alkaline water tank 25 acidic water pump 26 alkaline water pump 27 washing and drain tank 28, 29, 30, 31 automatic opening and closing valve

Claims (2)

[Claims] 1. An operation of supplying one or both of acidic water and alkaline water produced by electrolytically treating water to a filtration water side of a membrane filtration unit to wash the separation membrane with back-pressure water; A method for cleaning a membrane filtration device, comprising performing an operation of blowing air containing ozone into a water to be treated. 2. An operation of washing the separation membrane with an acidic water under a reverse pressure,
2. The method of claim 1, wherein the operation of backwashing the separation membrane with alkaline water and the operation of blowing air containing ozone into the water-to-be-treated side of the membrane filtration unit are performed according to a predetermined sequence and time interval. Cleaning method of membrane filtration device.