JPH11319517A - Membrane separation apparatus, membrane separation method, and method for washing membrane separation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane separation apparatus and a membrane separation method capable of carrying out continuous operation for a long duration by preventing fouling of membranes and to provide a method for washing the membrane separation apparatus by which membranes are efficiently washed in the case the membranes are fouled. SOLUTION: In a membrane separation method for filtering object water to be treated by a membrane element 2 immersed in a treatment tank 1 and solid-liq. separating the water, the object water is filtered while the membrane element 2 being washed by ultrasonic waves. In this case, based on high local energy of the cavitation-forming effect of ultrasonic waves and interface disturbing phenomenon and the likes, solid matter adhering to the membrane surface of the membrane element 2 and hardly to be shaken off and dirt in the insides of fine pores are efficiently separated, and solid matter is suppressed from adhering to the membrane surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for membrane separation, and a method for cleaning the same. The present invention relates to a membrane separation device and method and a cleaning method thereof.

[0002]

2. Description of the Related Art There are many methods for solid-liquid separation of wastewater and the like, and among them, a separation method using a membrane is currently attracting attention. The membrane separation method has many advantages such that clear treated water can be stably obtained and sludge can be concentrated. As a method that has received special attention in membrane separation,
There is an immersion film method. In this method, the membrane element is immersed in the water to be treated accommodated in the treatment water tank, and the membrane of the membrane element allows only the water in the water to be treated to permeate. In this case, the filtered water is permeated by applying pressure to the treated water side of the membrane or applying suction from the filtered water side of the membrane.

In general, the pressure applied to the treated water side of the membrane or the suction force applied from the filtered water side of the membrane is small from the viewpoint of reduction in operating power cost and strength of the membrane. Because of the permeation, it is necessary to increase the surface area of the membrane in order to obtain a predetermined amount of filtered water.

Therefore, when a flat membrane element is used as a membrane element, the flat membrane elements are stacked at a short pitch in a processing tank, so that the accommodation density of the membrane is increased. Similarly, a hollow fiber membrane or a tubular (tubular) membrane uses a membrane element obtained by bundling them.

By the way, when the water to be treated is filtered, suspended substances and polymer substances in the water to be treated remain on the membrane surface, and gradually adhere to or concentrate on the membrane surface, thereby reducing the permeability of the membrane element. .

Accordingly, a gas such as air is supplied from below the membrane element to perform aeration or bubbling, and a shearing force is applied to the membrane surface by a lifting action or a stirring action to reduce the adhesion of solids and the like. ing.

[0007] There is also a method of rotating the film instead of or together with the gas aeration (rotating flat film, etc.). There is also a method in which the membrane element is mechanically vibrated to reduce the adhesion of solids and the like.

[0008]

However, in a conventional membrane separation method in which a membrane is immersed in water to be treated containing a suspended substance or the like, and is simply filtered under pressure or under reduced pressure, the conventional membrane separation method has a disadvantage in comparison with precipitation separation. Although very clear treated water can be obtained, if filtration is continued, solids or the like adhere or enter the membrane surface or into the pores of the membrane, and the filtration performance gradually decreases.

Further, in a membrane separation method for bubbling a gas such as air from below the installed membrane element to prevent the adhered solids from being separated or adhered by utilizing the impact force of bubbles or the strong flow of generated water. Can suppress membrane occlusion, but its effect is generally insufficient and occlusion occurs at a considerable frequency. That is, since the shearing force applied to the membrane surface is small, solid matter attached to the membrane surface is likely to remain,
If the membrane separation process is continued, solid substances will adhere and the filtration resistance will increase. Therefore, if the pressure applied to the water to be treated side of the membrane or the suction force applied from the filtered water side is kept constant to perform the constant pressure filtration operation, the amount of the filtered water decreases, and the fixed filtration water amount is kept constant to perform the quantitative filtration operation. Attempting to do so increases the pressure difference between the water to be treated and the filtered water, so that the membrane separation process cannot be continued for a long time.

[0010] In addition, a method of rotating a membrane or a method of mechanically shaking a membrane module on which a membrane element is set to apply vibration to prevent the adhesion of solid matter is not enough to apply mechanical vibration. It is not possible to prevent solid matter from adhering to the pores and block the pores, and blockage occurs.

In any of the above-mentioned membrane separation methods, when the membrane becomes dirty or clogged, the treatment is interrupted, and the membrane surface is washed with a brush, or the membrane surface is immersed in a cleaning solution such as acid or alkali to clean the membrane surface. It is common to use a washing method in combination.
However, with this method, although the membrane surface can be washed to some extent, it has little effect on blocking in the pores,
There was a problem that the cleaning effect was insufficient and the blockage occurred relatively quickly after reuse.

In view of the above circumstances, the present invention has been made in view of the above circumstances, and has as its object to prevent a membrane from being clogged and to enable a long-term continuous operation, and to effectively perform membrane cleaning when the membrane is clogged. It is an object of the present invention to provide a method for cleaning a membrane separation device which enables the above.

[0013]

In order to achieve the above object, a membrane separation method of the present invention is directed to a membrane separation method in which water to be treated is filtered by a membrane element immersed and disposed in a treatment tank to perform solid-liquid separation. In addition, the water to be treated is filtered while ultrasonically cleaning the membrane element.

According to the present invention, a solid substance which adheres to the membrane surface of the membrane element and dirt in the pores are effectively peeled off by locally large energy having a cavitation action by ultrasonic waves, Adhesion of solid matter to the film surface can be suppressed.

Further, the method for cleaning a membrane separation device of the present invention comprises:
In a method for cleaning a membrane separation device in which water to be treated is filtered and solid-liquid separated by a membrane element immersed and disposed in a treatment tank, the membrane element is ultrasonically cleaned when the membrane of the membrane element is closed. And

According to the present invention, the locally large energy of the cavitation action by the ultrasonic wave can be used.
The solids that are hard to fall off and the dirt in the pores adhered to the membrane surface of the membrane element are effectively peeled off.

Further, the membrane separation apparatus of the present invention is a membrane separation apparatus for filtering water to be treated by a membrane element immersed and disposed in a treatment tank to perform solid-liquid separation. It is characterized by having a sound wave generator.

According to the present invention, the ultrasonic wave is applied to the water to be treated by the ultrasonic wave generator, and the solid matter adhered to the membrane surface of the membrane element due to the locally large energy having the cavitation action by the ultrasonic wave. And the dirt in the pores can be effectively peeled off, and the attachment of solid matter to the membrane surface can be suppressed. In addition, the present invention provides a method for cleaning a membrane element with ultrasonic waves when the membrane of the membrane element is closed due to locally large energy having cavitation action by ultrasonic waves. The dirt in the holes is effectively peeled off.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS.

FIG. 1 is a sectional view showing a first embodiment of the membrane separation apparatus of the present invention. As shown in FIG. 1, the membrane separation apparatus 10 includes a treatment tank 1, into which treatment water flows through a treatment water inflow line L1. In the water to be treated, a plurality of flat membrane elements as the membrane elements 2 stacked at predetermined intervals are immersed. The membrane element 2 can be replaced with an immersion membrane such as a hollow fiber membrane or a tubular membrane instead of the flat membrane element.
The types of these immersion films are RO film, NF film,
Any of a UF film, an MF film and the like can be used.

A water collecting pipe L2 is connected to each membrane element 2, and water permeating the membrane of the membrane element 2 is collected in each water collecting pipe L2 as filtered water. Each collecting pipe L2 is connected to a line L3. And the line L
A negative pressure is generated in the membrane element 2 by a suction pump (not shown) connected to 3, and the filtered water is sucked.

Further, an ultrasonic generator 11 is provided in the membrane separation apparatus 10, and the ultrasonic generator 11 applies ultrasonic waves to the water to be treated in the treatment tank 1. Ultrasonic generator 11
Consists of an oscillator that supplies a high-frequency current having the frequency of an ultrasonic wave and a vibrator that converts this high-frequency electric energy into ultrasonic vibration, which is mechanical energy. The oscillator is an oscillation circuit and active elements (transistors, thyristors, etc.) Depending on the purpose, a power output of several tens of watts and a power output of several tens of kilowatts can be obtained. Further, as the vibrator, a vibrator that uses an electrostriction phenomenon of a ceramic such as lead zirconate titanate or barium titanate, or a vibrator that applies a magnetostriction phenomenon such as nickel, ferrite, or alphero is used. The ceramic type is often used when a relatively high frequency of 100 to 400 kilocycles / sec is used, but is expensive, so the magnetostrictive phenomenon of nickel, ferrite, alphero, etc. is applied to the high output type. Oscillator is used, usually 20
It is used for a frequency of about 50 kilocycles / sec.

The ultrasonic cleaning uses cavitation. The force required to generate cavitation requires more power at higher frequencies,
Good cavitation effect even at low output for film cleaning 2
It is suitable to use one having a relatively low frequency of about 0 to 50 kilocycles / sec.

For example, in order to generate ultrasonic waves in the water to be treated by using a ferrite vibrator, the vibrator is immersed in the water to be treated as it is, or as shown in FIG.
The ferrite vibrator 3 may be used by bonding it to the bottom of the processing tank 1 made of a thin metal plate such as stainless steel. In the large processing tank 1, a large number of vibrators can be excited by a common winding. In addition to the method of directly using the vibrator as described above, a method of transmitting ultrasonic vibrations to the water to be treated via a horn for amplitude expansion and energy concentration can also be used.

In FIG. 1, the coil 4 and the bias magnet 5 constitute a part of an oscillation circuit, and a magnetic field generated by a high-frequency current flowing through the coil 4 and a magnetic field from the bias magnet 5 cause ferrite oscillation. The ultrasonic vibration generated in the ferrite vibrator 3 is applied to the water to be treated in the processing tank 1.

Next, the membrane separation apparatus 1 having the above-described configuration will be described.
The operation of 0 will be described.

In the membrane separation apparatus 10, the water to be treated in the treatment tank 1 for performing membrane separation is filtered by the membrane element 2 while applying ultrasonic waves. At this time, when ultrasonic waves are radiated from the ultrasonic generator 11 to the water to be treated, the water to be treated is subjected to a negative pressure (tension) for a certain period of one cycle, and the water to be treated is torn to a vacuum. Then, liquid or dissolved gas enters into it, forming bubbles. This bubble is compressed by receiving a positive pressure for the next period. As described above, the sound waves cause the bubbles to repeatedly expand and contract intensely, so that the expanded bubbles are almost in a state close to a vacuum, and the compressed bubbles become high-temperature and high-pressure and are explosively destroyed (cavitation phenomenon). At this moment, a large force acts, generating a shock wave of several thousand atmospheres. In addition, a stirring action by this large force occurs. Further, at the hetero-phase interface (liquid and film surface) where there is a difference in density, ultrasonic waves are remarkably reflected, and mechanical agitation is performed at the interface due to the reflected sound pressure. In other words, when ultrasonic waves are applied to the water to be treated, due to locally large energy having a cavitation effect and interface disturbance phenomena, solid substances adhered to the membrane surface and dirt in pores are effectively removed. At the same time, it is possible to prevent solid matter from adhering to the membrane surface, so that blockage of the membrane of the membrane element 2 is sufficiently prevented, and long-term stable operation becomes possible.

The application of ultrasonic waves may be performed intermittently at certain time intervals, instead of being performed continuously.

Next, a second embodiment of the membrane separation apparatus of the present invention will be described. The same or corresponding components as those of the first embodiment are denoted by the same reference numerals.

FIG. 2 is a sectional view showing a second embodiment of the membrane separation apparatus of the present invention. As shown in FIG. 2, in the treatment tank 1 of the membrane separation device 20, in addition to the ultrasonic generator 11, an air diffuser 6 is disposed below each of the membrane elements 2, and the air diffuser 6 is connected to a line L 4. It is connected. And the line L
The gas is supplied into the water to be treated through the air diffuser 6 by a blower (not shown) disposed at 4, and is aerated so as to form bubbles and rise. As the gas, air, oxygen and other gases can be used.

In such a membrane separation device 20, ultrasonic waves are applied to the water to be treated by the ultrasonic generator 11,
When the gas bubbling is performed, in addition to the cleaning effect by the ultrasonic wave, the shearing force due to the lifting action of the bubbles by the gas bubbling and the shearing force due to the simultaneously formed water flow are applied to the surface of the membrane element 2 and adhere to the membrane. The solids are removed, and the solids can be prevented from adhering to the film surface. Therefore, it is possible to extremely effectively prevent solid matter from adhering to the membrane surface and blockage in pores of the membrane, thereby enabling long-term stable operation.

Further, the cleaning methods of the first and second embodiments are not limited to the time when the membrane is separated, but once the solids adhere to the membrane to a predetermined degree or more and the pores are closed. Needless to say, this is also effective in the case where cleaning is performed in a state where the membrane separation process has been stopped. That is,
In the method using ultrasonic waves of the present invention, effective cleaning of the film can be performed by the strong cavitation effect on the film surface. In this case, the water to be treated in the treatment tank 1 or the treated water inside the membrane of the membrane element 2 is converted into acid (hydrochloric acid, sulfuric acid, citric acid, etc.), alkali (caustic soda, etc.), oxidizing agent (sodium hypochlorite, etc.). If the cleaning solution is replaced with a cleaning solution containing a reducing agent, a chelating agent or a surfactant, and ultrasonic waves are applied to these cleaning solutions, a synergistic effect of the shock wave generated by the ultrasonic waves and the cleaning power of the cleaning solution may be applied to deposits on the film surface. Not only that, there is also an effective peeling effect on the clogging in the pores, and more effective cleaning of the membrane surface becomes possible.

The membrane separation device and the membrane separation method of the present invention
It can be used for removing and concentrating suspended substances in the water to be treated or for removing dissolved salts and harmful substances. For example, river water, lake water, various wastewaters, separation of biological sludge such as activated sludge and methane fermentation, separation and concentration of coagulated sedimentation sludge, separation and removal of soluble salts and organic chlorine compounds, etc. Can be used in a wide range of fields.

[0034]

(Embodiment 1) An example in which the membrane separation method in the embodiment of FIG. 1 is applied to a biological treatment apparatus (activated sludge treatment) will be described below. The film area is 0.05 m ² (12.5 cm × 20
cm × 2 (both sides)) with a membrane distance of 13 m
m, and one membrane module obtained by stacking five membrane modules was placed in a processing bath (40 cm (w) × 25 cm) using a 600 W ultrasonic cleaning device.
(L) × 45 cm (h) = 45000 cm ³ ), 7000 mg / l of water to be treated was supplied as a suspended substance, and the suction filtration rate was set to 0.1 per minute while applying ultrasonic waves.
The membrane was separated at a setting of 7 l (1.0 m ³ / m ² / d). As a result, as shown in FIG. 3, the increase in the transmembrane pressure was slight until about two weeks after the start of the test. In FIG. 3, the horizontal axis represents the operation time of membrane filtration, and the vertical axis represents the membrane differential pressure at 25 ° C.

Comparative Example 1 Except that no ultrasonic wave was applied,
Filtration was performed under the same conditions as in Example 1. As shown in FIG. 3, the transmembrane pressure increased rapidly in about two days, and the membrane occlusion advanced.

(Example 2) An example in which the membrane separation method in the embodiment of FIG. 2 is applied to the same water to be treated used in Example 1 above is shown below.

The membrane area 0.05m ² (12.5cm × ²
0 cm x 2 (both sides)) with a membrane distance of 13
1 mm membrane module with a capacity of 600 W
Of the ultrasonic cleaning device in the treatment tank (40 cm (w) x 25 cm)
(L) × 45 cm (h) = 45000 cm ³ ), and 7000 mg / l of water to be treated was supplied as a suspended substance, ultrasonic waves were applied, and air was supplied from the lower part of the membrane element at 4 l / min. The suction filtration rate was set to 0.17 l / min (1.0 m ³ / m ²
/ D) to perform membrane separation. As a result, as shown in FIG. 3, the increase in the transmembrane pressure was slight even one month after the start of the test. That is, it was found that the combined use of bubbling cleaning was further improved as compared with the result of Example 1 in which only ultrasonic wave was applied.

(Example 3) The membrane area is 0.05 m ² (12.5 cm × 20 cm) by the membrane separation method in the form shown in FIG.
One membrane module in which five membrane elements of × 2 (both sides) are stacked at a distance of 13 mm between each membrane is treated with a 600 W ultrasonic cleaning device in a treatment tank (40 cm (w) × 25 cm (l)).
× 45 cm (h) = 45000 cm ³ ). Suspended matter About 30 mg / l of river water is supplied as the water to be treated, and while applying ultrasonic waves, the suction filtration rate is set to 0.26 l / min (1.5 m ³ / m ² / d) to perform membrane separation. Was done. As a result, as shown in FIG.
Until the day, the increase in transmembrane pressure was slight. In FIG. 4, the horizontal axis represents the operation time of membrane filtration, and the vertical axis represents the membrane differential pressure at 25 ° C.

(Comparative Example 2) Except that no ultrasonic wave was applied,
Membrane separation was performed under the same conditions as in Example 3. As a result, FIG.
As shown in the figure, the membrane pressure difference rapidly increased about 2 days after the start of the test, and the membrane occlusion progressed.

[0040]

As described above, according to the membrane separation apparatus and method of the present invention, the solid which adheres to the membrane surface due to the locally large energy of the cavitation action by ultrasonic waves and the interface disturbance phenomenon, etc. The substance and dirt in the pores are effectively peeled off, and the solid matter is prevented from adhering to the membrane surface. This prevents the membrane from being clogged during membrane separation and enables long-term continuous operation. Becomes

Further, according to the method for cleaning a membrane separation device of the present invention, solid substances adhered to the membrane surface and dirt in pores are effectively removed by locally large energy having cavitation action by ultrasonic waves. Peeled off.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a membrane separation device of the present invention.

FIG. 2 is a sectional view showing another embodiment of the membrane separation device of the present invention.

FIG. 3 is a graph showing the change over time of the filtration pressure difference for Examples 1, 2 and Comparative Example 1.

FIG. 4 is a graph showing the change over time in the filtration differential pressure for Example 3 and Comparative Example 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Processing tank, 2 ... Membrane element, 3 ... Ferrite vibrator (ultrasonic generator), 4 ... Coil (ultrasonic generator),
5: bias magnet (ultrasonic generator), 10, 20: membrane separation device.

Claims (6)

[Claims] 1. A membrane separation method for filtering water to be treated by a membrane element immersed and disposed in a treatment tank to perform solid-liquid separation, wherein the filtration of the water to be treated is performed while ultrasonically cleaning the membrane element. Characterized membrane separation method. 2. The method according to claim 1, wherein a gas is bubbled below the membrane element while ultrasonically cleaning the membrane element. 3. A method for cleaning a membrane separation device, wherein water to be treated is filtered and solid-liquid separated by a membrane element immersed and disposed in a treatment tank, wherein the membrane element is closed when the membrane of the membrane element is closed. A method for cleaning a membrane separation device, comprising performing ultrasonic cleaning. 4. The method for cleaning a membrane separation device according to claim 3, wherein a gas is bubbled below the membrane element while ultrasonically cleaning the membrane element. 5. The water to be treated outside the membrane and / or the water treated inside the membrane after the membrane of the membrane element is closed and before the membrane element is subjected to ultrasonic cleaning. 5. The method for cleaning a membrane separation device according to claim 3, wherein is replaced with a cleaning liquid. 6. A membrane separation device for filtering water to be treated by a membrane element immersed and disposed in a treatment tank and separating the solid and liquid, comprising an ultrasonic generator for ultrasonically cleaning the membrane element. Characteristic membrane separation device.