JPH0999226A - Washing method of membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a washing method of a membrane enabling to perfectly separate and remove a sticking object clogging a surface of the membrane, especially microorganisms without using the washing method of the membrane with a chemical liquid. SOLUTION: When the membrane clogged within the sticking object is washed by allowing the raw water 2 introduced in a filter tank 1 to transmit into a membrane module 3 and continuing solid-liquid separation, the filter tank inside 1 is maintained in an anaerobic state for a specified time by charging a reducing agent 5 or diffusing gaseous nitrogen, thus the sticking object is peeled off from the membrane, separated and removed.

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, in which raw water introduced into a filtration tank is permeated through a membrane module and solid-liquid separation is continued to efficiently wash a membrane clogged with a deposit. It is about.

[0002]

2. Description of the Related Art In a water treatment facility, raw water is passed through a filtration membrane and allowed to permeate to perform solid-liquid separation. In this membrane filtration device, a membrane module is immersed in a filtration tank, and raw water introduced into the filtration tank is filtered by a hollow fiber membrane of the membrane module. The permeated water is sent by a suction pump and provided as treated water for water purification.

In the above membrane filtration device, when the membrane filtration is continued, the membrane is clogged due to the adhered substances such as turbidity and the filtration efficiency is lowered. The membrane is washed by a method called backwashing in which it flows back to the raw water side, or the surface of the membrane is washed by air bubbles from an air nozzle provided below the membrane in the filtration tank.

Furthermore, after a certain period of time, the adhered substances such as turbidity penetrate into the inside of the membrane layer, and the cleaning effect by the above method is significantly reduced. Is removed from the apparatus, and the membrane is cleaned by immersing it in a chemical cleaning tank in which a cleaning chemical (acid / alkali) is stored. There has also been made an attempt to supply a cleaning chemical solution to the film without removing the film from the apparatus, and to remove the deposits on the film by the chemical solution.

[0005]

However, it is difficult to completely remove the deposits clogging the membrane by the above-mentioned conventional methods. Above all, if the adhered matter is an organic matter, a metal, etc., and if it is a microorganism, the removal work becomes more difficult. That is, particularly in a system in which water is not exchanged in the apparatus such as an immersion type membrane filtration apparatus, since the microorganisms are strongly attached to the surface of the membrane, the flux of the membrane is greatly reduced, and the conventional cleaning method is used. Then its removal is impossible at all. The conventional method of removing the membrane from the filtration device and immersing the membrane in the chemical cleaning tank requires equipment such as a crane for moving and removing / attaching the membrane. Further, the method of supplying the cleaning chemical to the membrane without removing the membrane from the apparatus has a drawback that it takes a lot of time to process the waste liquid after cleaning the chemical.

The present invention replaces such a conventional method of cleaning a membrane with a chemical solution and employs a method of removing the deposits from the membrane by keeping the inside of the filtration tank in an anaerobic state, thereby recovering the flux of the membrane. The purpose is to provide a cleaning method.

[0007]

As a concrete means for achieving the above-mentioned object, the present invention provides a method for permeating raw water introduced into a filtration tank through a membrane module to continue solid-liquid separation. When cleaning the membrane blocked with a kimono,
After maintaining the inside of the filtration tank in an anaerobic state for a predetermined time, the method for cleaning a membrane is characterized in that the adhering matter is separated from the membrane by air diffusion or the like to be separated and removed.

In this case, as a method of making the inside of the filtration tank anaerobic, a reducing agent (particularly sodium sulfite,
A method of introducing sodium hydrogen sulfite) or a method of replacing oxygen in the raw water in the filtration tank with nitrogen gas is effective. Further, in order to remove the deposits from the membrane after maintaining the anaerobic state, it is effective to blow the air sent from the blower into the filtration tank. Further, the membrane module may be a submerged filtration membrane.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a sectional view showing an example of an immersion type membrane filtration device for explaining the membrane cleaning method according to the present invention, and FIG. 1B is a perspective view of a membrane module. .

With reference to FIGS. 1 (a) and 1 (b), raw water 2 is introduced into a generally cylindrical filtration tank 1 having a conical lower portion by a known means. In the raw water 2, two membrane modules 3, which are submerged filtration membranes, are suspended horizontally in a horizontal arrangement. The membrane module 3 includes a hollow fiber membrane 3a (hereinafter, membrane 3
called a. 2) are integrated, and each film 3a has both ends connected to each other and both ends communicate with each other inside. The raw water 2 is sucked by the suction pump 10, permeates from the outer side of the membrane 3a of the membrane module 3 to the inner side of the membrane 3a, and is filtered. The permeated water 11 is the piping 1 on both sides of the membrane module 3.
It is taken out of the filtration tank 1 through a water supply pipe 13 connecting 8 and 19, and is sent to a treated water tank 17 by a suction pump 10 and provided as treated water 12 for purification. Reference numeral 15 is an opening / closing valve provided on the water supply pipe 13 on the side of the filtration tank 1 of the suction pump 10 and is in an open state during water supply.

A pipe 20 for backwashing is connected between the treated water tank 10 and the water supply pipe 13, and a backwash pump 21 and an on-off valve 1 are provided.
6 are interposed. When deposits are attached to the membrane 3a of the membrane module 3 to cause clogging, the suction pump 10 is stopped, the opening / closing valve 15 is closed, the opening / closing valve 16 is opened, and the backwash pump 21 is operated to operate the membrane. Compressed air and water are sent from the inside of 3a to perform back washing. It should be noted that sludge 22 which is an aggregate of deposits separated by the membrane 3a is stagnant at the bottom of the filtration tank 1.

When the membrane 3a is clogged by deposits, particularly microorganisms, on the membrane 3a during a certain period of time while continuing the membrane filtration, the supply of the raw water 2 is stopped, and After stopping the suction pump 10 and the backwash pump 21, the on-off valves 15 and 16 are closed to wash the membrane. As the first means, there is a method of introducing the reducing agent 5 into the raw water 2 stored in the filtration tank 1 to make the inside of the filtration tank 1 anaerobic. As the reducing agent, for example, water-soluble sodium sulfite, sodium bisulfite, and other known nontoxic compounds are selected. As a second means, there is a method of making the inside of the filtration tank 1 anaerobic by diffusing nitrogen gas. That is, the perforated pipe 6 is arranged in the raw water 2 stored in the filtration tank 1, the nitrogen gas is fed into the raw water 2 from the cylinder 7 storing the nitrogen gas, and the oxygen in the raw water 2 is replaced with the nitrogen gas. Is. By maintaining this anaerobic state for a predetermined time, specifically about 1 day or more, the adherent microorganisms are denatured and peeled off from the membrane surface to be separated and removed. If the redox potential is further lowered in the anaerobic state, many of the metals become soluble in the reduced state,
It is also possible to effectively remove clogging of metal and the like. Further, after the inside of the filtration tank 1 is maintained in an anaerobic state for a predetermined time, the membrane may be vibrated to remove the deposits from the membrane. Further, back washing may be performed instead of vibration. Next, air is sent from the blower 9 into the filtration tank 1, and the adhered microorganisms are removed from the membrane by an air diffuser that blows the air into the raw water 2 evenly by forming fine bubbles in the porous tube 8 arranged in the raw water 2. After the peeling, the operation is restarted. In this case, the air from the air diffuser may hit the surface of the membrane. The water in the filtration tank 1 is drained if necessary.

In the above embodiment, an example in which two membrane modules are suspended in raw water has been described.
Increases or decreases depending on the scale. Further, the membrane module may use a flat membrane, a spiral membrane, a tubular membrane or the like instead of the hollow fiber membrane.

[0014]

As described above, according to the membrane cleaning method of the present invention, the method of anaerobicizing the inside of the filtration tank to remove the deposits from the membrane is used, so that the membrane firmly adheres to the surface of the membrane. The deposits clogging the membrane, especially the microorganisms, were deteriorated and peeled off while maintaining the anaerobic state in the filtration tank, and the flux of the membrane could be largely recovered. Therefore, it is possible to completely remove the deposit, which was difficult with the conventional cleaning method.
Then, the equipment for moving and removing / attaching the membrane, such as a crane, which is required in the conventional method of removing the membrane from the filtration device and immersing it in the chemical cleaning tank is not required. Also, the waste liquid treatment after chemical cleaning, which requires the conventional method of supplying a cleaning chemical to the film without removing it from the device, is not necessary when nitrogen gas is diffused, and when a reducing agent is added. Also has the effect of requiring a small amount of waste liquid.

[Brief description of drawings]

FIG. 1 (a) is a cross-sectional view showing an example of a submerged membrane filtration device for explaining a membrane cleaning method according to the present invention, and FIG. 1 (b) is a perspective view of a membrane module.

[Explanation of symbols]

 1 ... Filtration tank 2 ... Raw water 3 ... Membrane module 3a ... Hollow fiber membrane 5 ... Reducing agent 6 ... Porous tube 7 ... Cylinder 8 ... Porous tube 9 ... Blower 10 ... Suction pump 11 ... Permeate 12 ... Treated water 13 ... Water pipe 15 ... Open / close valve 16 ... Open / close valve 17 ... Treatment water tank 18 ... Piping 19 ... Piping 20 ... Piping 21 ... Backwash pump 22 ... Sludge

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Genzo Ozawa, 12-3-23 Kita 33, Kita-ku, Sapporo-shi, Hokkaido (72) Inventor Tatsuhiko Suzuki 1-3-3 Kyobashi, Chuo-ku, Tokyo Maesawa Industry Co., Ltd. In the company

Claims (6)

[Claims] 1. When the raw water introduced into the filtration tank is permeated through the membrane module and solid-liquid separation is continued to wash the membrane clogged with the deposits, the filtration tank is anaerobic for a predetermined time. A method for cleaning a film, characterized in that after maintaining, the deposit is separated from the film to be separated and removed. 2. The method for cleaning a membrane according to claim 1, wherein a reducing agent is introduced into the filtration tank to make the inside of the filtration tank anaerobic. 3. The method for cleaning a membrane according to claim 2, wherein the reducing agent is sodium sulfite or sodium hydrogen sulfite. 4. The method for cleaning a membrane according to claim 1, wherein oxygen in the raw water in the filtration tank is replaced with nitrogen gas to make the inside of the filtration tank anaerobic. 5. The method for cleaning a membrane according to claim 1, wherein air sent from a blower is blown into the filtration tank to remove the deposits from the membrane. 6. The method for cleaning a membrane according to claim 1, wherein the membrane module is an immersion type filtration membrane.