JP3430385B2 - Cleaning method of membrane - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention permeates raw water introduced into a filtration tank through a membrane module and continues solid-liquid separation, whereby the raw water is blocked by deposits. The present invention relates to a method for cleaning a film for efficiently cleaning the film. 2. Description of the Related Art In a water treatment facility, raw water flows through a filtration membrane and is permeated 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-mentioned membrane filtration apparatus, if the membrane filtration is continued, the membrane is clogged by a deposit such as turbidity and the filtration efficiency is reduced. The membrane is washed by a method called back washing, in which the membrane 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. Further, after a certain period of time, deposits such as turbid substances enter into the inside of the membrane layer, and the cleaning effect by the above-mentioned method is remarkably deteriorated. Is removed from the apparatus, and immersed in a chemical cleaning tank in which a cleaning chemical (acid / alkali) is stored to clean the membrane. Also, attempts have been made to supply a chemical solution for cleaning to the film without removing the film from the apparatus, and to remove deposits on the film with the chemical solution. [0005] However, it is difficult to completely remove the deposits blocking the film by each of the above-mentioned conventional methods. Above all, if the attached matter is an organic matter, a metal or the like, and if the attached matter is a microorganism, the removing operation becomes more difficult. That is, especially in a system such as an immersion type membrane filtration device in which the water exchange in the device is relatively small, 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 it is impossible to remove it. In the conventional method of removing the membrane from the filtering device and immersing the membrane in the chemical solution cleaning tank, equipment such as a crane for moving, removing, and attaching the membrane is required. Further, the method of supplying a chemical solution for cleaning to the film without removing the film from the apparatus has a disadvantage that it takes time and effort to treat a waste liquid after the chemical solution cleaning. The present invention employs a method in which the inside of a filtration tank is made anaerobic to remove deposits from the membrane, instead of the conventional method of cleaning a membrane with a chemical solution, thereby recovering the flux of the membrane. It is intended to provide a cleaning method. [0007] As a specific means for achieving the above object, the present invention is to permeate raw water introduced into a filtration tank through a membrane module and continue solid-liquid separation. As a result, in cleaning the membrane clogged with the deposit,
The membrane is blocked while maintaining the anaerobic state in the filtration tank for a predetermined time
Transforms and separates and removes attached microorganisms.
And by lowering the oxidation-reduction potential,
A method for cleaning a film, comprising removing a reactive metal . In this case, as a method for 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 raw water in a filtration tank with nitrogen gas is effective. Further, in order to separate the deposits from the membrane after maintaining the anaerobic state, it is effective to blow air sent from a blower into the filtration tank. Further, the membrane module may be an immersion filtration membrane. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A 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. 1B is a perspective view of a membrane module. . Referring 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 known means. In the raw water 2, two membrane modules 3, which are immersion-type filtration membranes, are vertically suspended in a horizontal arrangement. The membrane module 3 includes a hollow fiber membrane 3a (hereinafter, membrane 3).
called a. ) Are integrated, and the individual films 3a are connected at both ends thereof and communicate with the inside at both ends. The raw water 2 is sucked by the suction pump 10 and permeates from the outside of the membrane 3a of the membrane module 3 to the inside of the membrane 3a to be filtered. The permeated water 11 is supplied to the piping 1 on both sides of the membrane module 3.
The water is taken out of the filtration tank 1 through a water supply pipe 13 connecting the pipes 8 and 19, sent to a treatment water tank 17 by a suction pump 10, and provided as treatment water 12 for water purification. Reference numeral 15 denotes an opening / closing valve interposed on the filtration tank 1 side of the suction pump 10 on the water supply pipe 13, and is open during water supply. A backwashing pipe 20 is connected between the treated water tank 10 and the water pipe 13, and a backwash pump 21 and an on-off valve 1 are provided.
6 are interposed. When deposits adhere to the membrane 3a of the membrane module 3 and clogging occurs, the suction pump 10 is stopped, the on-off valve 15 is closed, the on-off 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. At the bottom of the filtration tank 1, sludge 22, which is an aggregate of attached matter separated by the membrane 3a, is stagnating. [0012] When a certain period of time elapses while the membrane filtration is continued and the deposits, especially microorganisms, accumulate on the membrane 3a and the membrane 3a is closed, the supply of the raw water 2 is stopped. After the operation of the suction pump 10 and the backwash pump 21 is stopped, the on-off valves 15 and 16 are closed, and the membrane is washed. As the first means, there is a method in which the reducing agent 5 is charged into the raw water 2 stored in the filtration tank 1 to make the inside of the filtration tank 1 an anaerobic state. As the reducing agent, for example, water-soluble sodium sulfite, sodium hydrogen sulfite and other known non-toxic compounds are selected. As a second means, there is a method in which the inside of the filtration tank 1 is made anaerobic by diffusing nitrogen gas. That is, a perforated pipe 6 is arranged in raw water 2 stored in a filtration tank 1, nitrogen gas is sent into the raw water 2 from a cylinder 7 storing nitrogen gas, and oxygen in the raw water 2 is replaced with nitrogen gas. It is. By maintaining this anaerobic state for a predetermined period of time, specifically, about one day or more, the attached microorganisms are degenerated and separated from the membrane surface, and separated and removed. If the oxidation-reduction potential is further reduced in the anaerobic state, most of the metals become soluble in the reduced state,
The clogging of metal or the like can be effectively removed. Alternatively, after maintaining the inside of the filtration tank 1 in an anaerobic state for a predetermined time, the film may be vibrated to separate the deposit from the film. 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 a diffuser that uniformly blasts the raw water 2 into fine bubbles with a porous tube 8 arranged in the raw water 2. After peeling, the operation is resumed. In this case, the air from the air diffuser should preferably hit the surface of the membrane. The water in the filtration tank 1 is drained as needed. In the above embodiment, an example in which two membrane modules are suspended in raw water has been described.
It is increased or decreased according to 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. As described above, according to the method for cleaning a membrane according to the present invention, the method of anaerobicizing the inside of the filtration tank and removing the deposits from the membrane is adopted. Deposits, especially microorganisms, which adhered tightly and blocked the membrane, were altered 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 deposits, which is difficult with the conventional cleaning method.
In addition, equipment for moving, removing, and attaching the membrane, such as a crane, which required the conventional method of removing the membrane from the filtration device and immersing it in the chemical solution cleaning tank, is not required. In addition, the conventional method of supplying a chemical solution for cleaning to a membrane without removing the membrane from the apparatus is necessary, and the waste liquid treatment after chemical solution washing is unnecessary when diffusing nitrogen gas, and when a reducing agent is supplied. This also has the effect of requiring only a small amount of waste liquid.

BRIEF DESCRIPTION OF THE 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 membrane module. It is a perspective view of. [Description of Signs] 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 ... permeated water 12 ... treatment Water 13 ... Water supply pipe 15 ... On-off valve 16 ... On-off valve 17 ... Treatment water tank 18 ... Pipe 19 ... Pipe 20 ... Pipe 21 ... Backwash pump 22 ... Sludge

Continuation of the front page (72) Inventor Tatsuhiko Suzuki 1-3-3 Kyobashi, Chuo-ku, Tokyo Inside Maezawa Industrial Co., Ltd. (56) References JP-A-7-155789 (JP, A) JP-A-55-129107 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 65/02 520 B01D 65/06 C02F 1/44

Claims (1)

(57) [Claims 1] In washing the membrane clogged with deposits, the raw water introduced into the filtration tank is allowed to permeate through the membrane module and solid-liquid separation is continued. While maintaining the inside of the filtration tank in an anaerobic state for a predetermined time , attached microorganisms blocking the membrane are removed.
Degradation and peeling, separation and removal, and oxidation-reduction
A method for cleaning a film, comprising: removing a soluble metal by lowering a position .