JPH11128698A - Back pressure water cleaning method and device for water treatment filtration membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device capable of efficiently removing a flow passage blocking, etc., due to an adhered layer on a surface of the membrane, clogging and solid matter without increasing a chemical washing number as a washing method of the membrane to which the sludge material is stuck, in the treating method of a sludge material in the water to be treated with the membrane. SOLUTION: The device has a structure in which a first electrode 2 provided at a side of filtered water by contacting with a filter membrane 1 and its pair second electrode 4 are added to a membrane module arranged with the filter membrane 1 between a side of the water to be treated and the side of the filtered water. When the clogging is generated at the membrane, the washing with an alkali water or an acid water is executed together with a physical washing and an effective washing effect is obtained by making electric current flow between both the electrodes 2, 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtration apparatus for all water treatments for separating and removing pollutants contained in water and a control method thereof.

[0002]

2. Description of the Related Art In water treatment using a membrane, pollutants gradually adhere to the membrane during operation. As a method of cleaning the membrane to which the pollutants adhere, a physical cleaning method and a chemical cleaning method are used. Have been. As the physical cleaning method, there are methods such as back pressure water cleaning in which membrane filtered water flows backward, flushing with a water flow on the primary side of the membrane, and back pressure air cleaning in which pressurized air is passed from the secondary side of the membrane. These methods are effective for recovering performance deterioration due to fouling such as an adhered layer on the surface of the membrane, clogging, and blockage of a flow path by solid matter, and generally, cleaning is performed once every 10 to 120 minutes of operation time. Has been done.

On the other hand, the chemical cleaning method is a cleaning method in which a substance that cannot be removed by the physical cleaning method is removed by decomposing or dissolving with a chemical. Chemicals for cleaning include caustic soda, sodium hypochlorite, and alkaline detergents for removing organic substances, and hydrochloric acid, sulfuric acid, oxalic acid, citric acid, and pickling agents for removing inorganic substances. ,
Used. This chemical cleaning is generally performed about once every one to several months.

[0004]

However, in the above-mentioned method for cleaning a membrane, when the quality of raw water is extremely polluted, there is a problem that not only the number of physical cleanings but also the number of chemical cleanings are increased. . This increase in the number of times of chemical cleaning not only raises operating costs due to an increase in the amount of chemicals used and an increase in the area of the chemical storage facility, but also by filtration through the membrane to remove chemicals remaining on the membrane after chemical cleaning. Since the treated water used as the rinsing water is used, the amount of treated water obtained from the entire membrane treatment facility is reduced.

It is an object of the present invention to provide a cleaning method for effectively removing an adhered layer, clogging, and blockage of a flow path by a solid substance without increasing the number of times of chemical cleaning.

[0006]

Means for Solving the Problems In order to achieve the above object, in the present invention, a pollutant of the water to be treated is filtered by a membrane, and when clogging is caused by the pollutant,
In the method of back pressure water washing using filtered water, (1). A conductive filter arranged in contact with the filtered water is used as the first electrode, and a means is provided for passing a current between the first electrode and the second electrode that forms a pair with the first electrode. Backwash with water.

(2). In addition, by means of (1), the DC power supply applies a positive voltage to the first electrode and a negative voltage to the second electrode, or vice versa, and applies a negative voltage to the first electrode and a positive voltage to the second electrode. It should be washed with pressurized water. Also, (1),
As an apparatus for specifically performing the method (2), a membrane module including a filtration membrane, a water tank to be treated, a filtered water tank,
And the like, wherein the contaminated substances of the water to be treated are filtered by a membrane, and when clogging is caused by the contaminated substances, the apparatus is subjected to back-pressure water washing using filtered water. (3). A first electrode of a conductive filter arranged to be in contact with the filtered water in the membrane module, and a second electrode that is a pair of the first electrode, further comprising a DC power supply, and a polarity switch It should be backwashed with the equipment.

Further, the conductive filter of (3)
(4). (5). It is made of a conductive inorganic or organic material having a molecular weight cut off of at least 1000; Porous material made of a non-conductive inorganic or organic material having a molecular weight cutoff of at least 1000 and a conductive mesh or porous having a pore size of 0.01 μm or more in average size,
(6). A conductive material is formed by vapor deposition or firing on a porous material made of a nonconductive inorganic or organic material having a molecular weight cutoff of at least 1,000.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a membrane module which is a main part of the present invention. The principle of removing a deposit on a membrane will be described with reference to FIG. The structure of the membrane module is shown in Fig. 1.
The filtration membrane 1 is disposed so as to separate the membrane module into two chambers, ie, the treated water side and the filtered water side, and the first electrode 2 disposed in contact with the filtration membrane 1 and disposed on the filtered water side. And a second electrode 4 arranged so as to form a pair of the first electrode on the filtered water side, and a means for flowing a current between the first and second electrodes is provided. In the membrane module having this structure, the contaminants in the water to be treated flowing from the water inlet 5 for treatment are filtered by an electrically conductive filter which is usually composed of the filtration membrane 1 and the adjacent first electrode 2.

Here, when the film is clogged,
In a state where electricity is supplied between the first electrode 2 and the second electrode 4, the inflow of the water to be treated is stopped from the water inlet 5, and the reverse pressure water inlet 8 is stopped.
Reverse pressure water washing is performed in which filtered water is passed through and the washing water is discharged from the counter pressure water outlet 9 to remove deposits on the membrane surface. When a current is applied between both electrodes during back pressure water cleaning, cleaning having the effect of ionic water is performed simultaneously with normal physical cleaning.

When a direct current is applied between the first electrode and the second electrode with the first electrode being negative and the second electrode being positive, OH ^- is generated at the first electrode by the following reaction. Generates and becomes alkaline water.

[0012]

## STR1 ## 2H ₂ O + 2e → H ₂ + 2OH ⁻ 1 / 2O ₂ + H ₂ O + 2e → 2OH ^—In this state, water is pumped from the filtered water side to the raw water side to reduce the adhesion layer on the membrane surface and clogging substances On the other hand, physical cleaning and chemical cleaning with alkaline water are performed simultaneously.

On the other hand, when a direct current is applied between the first electrode and the second electrode with the first electrode being positive and the second electrode being negative, H is applied to the first electrode by the following reaction. ⁺ Is formed and becomes acidic water.

[0014]

2H ₂ O-2e → 1 / 2O ₂ + 2H ^{+ In} this state, water is pumped from the filtered water side to the raw water side to physically clean the adhered layer and clogged substances on the membrane surface. Chemical cleaning with acid water is performed at the same time.

As for the polarity of the voltage applied between the electrodes, either one of them can be selected, or a method of alternately performing both at a certain time can be selected. That is, the most effective method can be adopted depending on the type of the pollutant contained in the water to be treated. The application of these voltages can be easily realized by providing a DC power supply and a polarity switch.

The conductive filter, which is a main component of the present invention, may be arranged such that the filtration membrane and the first electrode are in contact with each other, or the filtration membrane and the first electrode may be integrally formed. good. In the case of integral type, the usual water treatment is ultrafiltration (U
F) Since a membrane is used, a necessary condition is that the filtration membrane is a porous body made of an inorganic or organic material having a molecular weight cut off of at least 1,000. At that time, there are various configurations of the electrode adjacent to the filtration membrane, and even a filtration membrane made of a conductive material is coarser than an ultrafiltration (UF) membrane and has a pore size of 0.01 μm or more. The filter may be a conductive mesh or a filter having porous media adjacent to a microfiltration (MF) membrane having an average size, or may be a filter formed by vapor deposition or firing of a conductive substance.

[Examples] Next, specific examples of a few structures and measurement results will be shown as examples. FIG. 3 is a schematic cross-sectional view of an internal pressure hollow fiber membrane module used to demonstrate the present invention, FIG. 4 is a schematic cross-sectional view of an internal pressure tube type membrane module, and FIG. It is a cross section schematic diagram. The present invention is applicable to both types.

FIG. 2 shows a schematic flow chart of a filtration experiment used to demonstrate the present invention. A turbidity of 100 ° C. and a total organic carbon concentration TOC of 10 mg / L are treated water, and the volume is 50
L to be treated in the treated water tank 10 in advance, and the treated water pump 13 is used to measure 1 L / m
The flow rate is adjusted to “in”, and water is passed through the membrane module 11 via the check valve 19. The flow rate of the filtered water is measured by a flow meter 17 and stored in a filtered water tank 12 having a volume of 20 L.
After filtering for one hour, the water pump 13 is stopped. Next, the filtered water in the filtered water tank 12 is sent to the membrane module 11 by the back pressure water pump 14, and
From the converter 18, the first electrode 2 and the second electrode 4 were used as conductive filters, in which a flat membrane having a cut-off molecular weight of 1000 and a porous carbon having a pore diameter of 1 μm were adjacent to each other. And the first 15 seconds are negative to the first electrode 2,
The second electrode 4 was energized as positive, followed by switching between positive and negative by the converter 18 for 15 seconds to energize the first electrode 2 as positive and the counter electrode 4 as negative.

FIG. 6 shows the experimental results when the internal pressure hollow fiber membrane module shown in FIG. 3 was used. In this figure, the horizontal axis represents the filtration time, and the vertical axis represents the permeation flux (the value obtained by dividing the permeation flow rate by the membrane area). Also, the thin line in the figure shows the measurement results when physical cleaning with conventional counter-pressure water was performed, and the thick line shows the measurement results when electricity was applied during cleaning with counter-pressure water according to the present invention. From this, as is apparent, when only the conventional physical cleaning is performed,
The permeation flux is not completely recovered and the first physical cleaning
The permeation flux decreased in the second order. On the other hand, according to the present invention, it can be seen that the permeation flux is almost recovered by washing.

Similar results were obtained when the internal pressure tube type membrane module shown in FIG. 4 and the conductive internal pressure tube type membrane module shown in FIG. 5 were used.

[0021]

As described above, according to the present invention, the conductive filter arranged to be in contact with the filtered water when backwater pressure washing is performed to remove the adhesion layer and clogging on the surface of the membrane. Backwashing with filtered water in a state where current is passed between the first electrode and the counter electrode. In this way, it is possible to remove organic and inorganic substances that cannot be removed by physical cleaning normally performed, and to recover the permeation flux of the filtration membrane,
It is possible to maintain the amount of treated water, and the chemical equipment is not required, so that the installation area is small and the space can be saved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a filtration device of the present invention.

FIG. 2 is a schematic flow diagram of a filtration experiment used to demonstrate the present invention.

FIG. 3 is a schematic cross-sectional view of an internal pressure hollow fiber membrane module used to demonstrate the present invention (a conductive filter combining a nonconductive porous and conductive mesh).

FIG. 4 is a schematic cross-sectional view of an internal pressure tube type membrane module used to demonstrate the present invention (a conductive filter combining a nonconductive porous and conductive mesh).

FIG. 5 is a schematic cross-sectional view of an internal pressure tube type membrane module used to demonstrate the present invention (conductive filter made of conductive porous material).

FIG. 6 is a comparison diagram of the results of a verification test using the method of the present invention and the conventional method (relation between filtration time and permeation flux)

[Explanation of symbols]

 1: Filtration membrane 2: First electrode 3: Partition wall 4: Second electrode 5: Treated water inlet 6: Condensed water outlet 7: Filtration water outlet 8: Back pressure water inlet 9: Back pressure water outlet 10: Treated water Tank 11: Membrane module 12: Filtration water tank 13: Treated water pump 14: Back pressure water pump 15: Power supply 16: Flow meter 17: Flow meter 18: Converter 19: Check valve

Claims (6)

[Claims] 1. A method of filtering contaminated substances of a water to be treated by a membrane and, when clogging is caused by the contaminated substances, performing back-pressure water washing using filtered water so as to be in contact with the filtered water. The arranged conductive filter is used as the first electrode, and a means for passing an electric current between the first electrode and the second electrode which is a pair thereof is provided. Back pressure water washing method for water treatment filtration membrane. 2. The method according to claim 1, wherein the DC power supply applies a positive voltage to the first electrode and a negative voltage to the second electrode, or vice versa. Back pressure water cleaning method characterized by performing back pressure water cleaning in a state where the voltage is applied. 3. A membrane module including a filtration membrane, a water tank to be treated, a filtered water tank, and the like, wherein a pollutant of the water to be treated is filtered by a membrane, and when clogging is caused by the pollutant, the filtered water In the apparatus for back pressure water washing using, the first electrode of the conductive filter arranged to be in contact with the filtered water in the membrane module, and a second electrode that is a pair of the first electrode, further comprising A back pressure water washing apparatus for a water treatment filtration membrane, comprising a DC power supply and a polarity switch. 4. The method according to claim 3, wherein the conductive filter is made of a porous material made of a conductive inorganic or organic material having a molecular weight cut-off of at least 1,000. apparatus. 5. The method according to claim 3, wherein the conductive filter is made of a non-conductive inorganic or organic material having a molecular weight cut-off of at least 1000 and an average pore size of 0.01 μm or more. A back-pressure water washing apparatus characterized in that a conductive mesh or a porous material having a dimension is adjacent to the conductive mesh. 6. The method according to claim 3, wherein the conductive filter is formed by depositing or firing a conductive substance on a porous nonconductive inorganic or organic material having a molecular weight cut off of at least 1000. Back pressure water cleaning device characterized by being made.