JPH1066844A - Cleaning method for membrane separation equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for cleaning an immersion type membrane separation device capable of obtaining a stable cleaning effect without using a high concentration chemical solution. SOLUTION: A chemical solution for decomposing a substance adhering to a membrane surface is injected into a permeated water flow channel 15b of a membrane cartridge 15 of a membrane separation device 7 to permeate a filtration membrane 15a, and the permeated water flow channel 1
Hold for 1-2 hours in 5b. Then, the permeated water channel 15
a) into the filter membrane 15 by injecting substantially the same amount of washing water as the chemical solution.
a. As a result, the substance adhering to the membrane surface can be efficiently removed to recover the transmembrane pressure difference, and the permeated water flow path 1 can be recovered.
Disposal of the chemical solution remaining in 5b can be made unnecessary.

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 an immersion type membrane separation apparatus which is installed inside an aeration tank and filters an activated sludge mixture in the tank.

[0002]

2. Description of the Related Art As a system for treating organic wastewater such as domestic wastewater, such as a merger treatment septic tank, a system utilizing a membrane separation device has been put into practical use. It is as shown in FIG.

[0003] Sewage is sequentially introduced into the coarse screen 1 and the flow control tank 2 to remove impurities and adjust the flow rate, and the sewage 3 having an appropriate flow rate is allowed to flow into the denitrification tank 4 and the nitrification tank 5 sequentially. By returning a part of the activated sludge mixture in the nitrification tank to the denitrification tank 4 as the circulating liquid 6, nitrogen and organic substances in the wastewater are biologically removed by the activated sludge, and the remaining nitrification tank is also removed. The activated sludge mixture is filtered by a membrane separator 7 to take out the permeated water 8, and the activated sludge is left in the tank. The membrane permeated water 8 is sent to a disinfecting tank 9 for disinfection and then discharged as treated water 10, and the sludge 11 accumulated in the nitrification tank 5 is appropriately extracted and sent to a residue sludge storage tank 12, and once stored, It is carried out as waste sludge 13 and disposed of.

The membrane separator 7 is as shown in FIG. 3, in which a flat membrane cartridge 15 is arranged in parallel at a predetermined interval in an upper portion of a box frame-shaped case 14 having an open top and bottom. An aeration device 16 is provided below the cartridge 15, and a water collecting pipe 18 that communicates with a permeated water flow path (not shown) of each membrane cartridge 15 via a membrane permeated water tube 17 is provided above the case 14. , A membrane permeated water outlet pipe 19 is provided in communication with the water collection pipe 18.

[0005] In such a membrane separation device 7, a pressure difference is generated on both sides of the filtration membrane 15 a by applying a suction pressure to the permeated water channel of each membrane cartridge 15 through the membrane permeated water outlet pipe 19, for example. The activated sludge is captured by the filtration membrane 15a of each membrane cartridge 15, and the membrane permeated water that has passed through the filtration membrane 15a and flowed into the membrane permeated water flow path is passed through the membrane permeated water tube 17, the water collection pipe 18, and the membrane permeated water outlet pipe 19. Through the tank. At this time, the membrane surface is cleaned using air bubbles ejected from the aeration device 16.

When the pores of the filtration membrane 15a are clogged by the above-mentioned membrane surface cleaning and the transmembrane pressure is reduced, the entire membrane separator 7 or the membrane cartridge 15 is taken out of the tank. The membrane is washed by injecting a chemical solution into the membrane permeated water flow path while the membrane separator 7 is immersed in the tank, and the latter is becoming the mainstream because the latter method of washing in the tank is easy. .

[0007]

However, in the above-described method for cleaning the inside of the tank, it is difficult to uniformly clean the filtration membrane with a chemical solution, so that the permeability of the filtration membrane is difficult to stabilize, and the chemical solution is difficult to clean. There is a problem that the concentration of the drug solution cannot be increased because it may adversely affect microorganisms.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a method for cleaning a membrane separation apparatus capable of obtaining a stable cleaning effect without using a high-concentration chemical solution.

[0009]

In order to solve the above-mentioned problems, a method for cleaning a membrane separation apparatus according to claim 1 of the present invention comprises:
A method for cleaning an immersion type membrane separation device that is installed inside an aeration tank and filters the activated sludge mixture in the tank, and injects a chemical solution that decomposes substances adhering to the membrane surface into a permeate flow path of the membrane separation device. And permeate the filtration membrane, and maintain the state in which the chemical solution in the permeated water flow path is in contact with the filtration membrane for 1 to 2 hours, and then inject substantially the same amount of washing water as the chemical solution into the permeated water flow path. The filter is made to pass through a filtration membrane.

[0010] The method for cleaning a membrane separation device according to claim 2 is as follows.
3 to 4 L of a chemical solution per 1 m ^{2 of the} filtration membrane is injected at a flux higher than the permeated water flux during the filtration operation.
According to the configuration described above, while the chemical liquid is in contact with the filtration membrane for 1 to 2 hours, the substance adhering to the pores of the filtration membrane and the substance adhering to the membrane surface are decomposed and dissolved by the reaction with the chemical liquid. And
Part of the substance attached to the membrane surface on the membrane surface is separated from the filtration membrane. Then, by the pressure of the water permeating from the permeate side of the filtration membrane to the liquid to be treated, the remaining substance adhering to the membrane surface which is easily peeled off by the chemical solution is also peeled off from the filtration membrane. As a result, clogging of the filtration membrane is eliminated, and the transmembrane pressure is increased. Since the unreacted chemical in the permeated water flow path is pushed out to the liquid to be treated by the water, the unreacted chemical is prevented from being taken out when the filtration is restarted.

If 3 to 4 L of a chemical solution per 1 m ^{2 of the} filtration membrane is injected at a flux higher than the permeated water flux during the filtration operation, the substances adhering to the membrane are efficiently decomposed and dissolved, and are separated from the membrane surface. When the water to be treated is organic wastewater, it is efficient to inject sodium hypochlorite at a concentration of about 0.5% by weight or more. However, when the total amount of sodium hypochlorite to be injected is large, the microorganism is adversely affected. Therefore, the activated sludge is injected in a range of 5% or less, preferably 3% or less of the dry weight of the activated sludge.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of the nitrification tank 5 in the sewage treatment flow described with reference to FIG. 2, and an immersion type membrane configured similarly to that described with reference to FIG. A separation device 7 is provided.

Each membrane cartridge 15 of the membrane separation device 7 has:
A membrane permeated water channel 15b is provided inside the filtration membrane 15a, and the membrane permeated water tube 1 is provided in the membrane permeated water channel 15b.
7. The water collecting pipe 18 and the membrane permeated water outlet pipe 19 communicate with each other.
A washing pipe 20 for injecting a chemical is open in the conduit of the membrane permeated water outlet pipe 19.

In such a configuration, during the filtration operation, the activated sludge mixed liquid 22 in the tank is filtered by the filtration membrane 15a, and the membrane permeated water that has passed through the filtration membrane 15a and flowed into the membrane permeated water channel 15b is removed. It is taken out of the tank through the membrane permeated water tube 17, the water collection tube 18, and the membrane permeated water outlet tube 19.

Then, when the pores of the filtration membrane 15a are clogged and the transmembrane pressure difference is reduced, or periodically, the washing is performed as follows. Activated sludge mixture 22
With the membrane separation device 7 immersed in the washing tube 20,
Membrane permeated water outlet pipe 19, water collecting pipe 18, membrane permeated water tube 1
7, through the membrane permeate channel 15 of each membrane cartridge 15.
A 0.5% aqueous sodium hypochlorite solution in an amount corresponding to 3 to 4 L per 1 m ² of the filtration membrane 15 a is injected into the inside of b so as to have a flux substantially equal to the permeation flux during the filtration operation. And
The filtration membrane 15a is permeated in a direction opposite to that in the filtration operation. Thereafter, the aqueous solution of sodium hypochlorite in the membrane permeated water channel 15b is left for 1 to 2 hours in a state of being in contact with the filtration membrane 15a. As a result, the substance adhering to the surface of the membrane or the substance adhering to the surface of the membrane that has entered the pores of the filtration membrane 15a is decomposed and dissolved by the reaction with sodium hypochlorite, and a part of the substance adhering to the surface of the membrane Peel from

Thereafter, in the same manner as above, a permeate of substantially the same amount as the aqueous solution of sodium hypochlorite is introduced from the washing pipe 20 into the membrane permeate passage 15b of each membrane cartridge 15 during the filtration operation. Is injected so as to have a flux substantially equal to the above, and is permeated through the filtration membrane 15a in a direction opposite to that during the filtration operation. Thereby, the remaining substance adhering to the film surface which is easily peeled off by the sodium hypochlorite is peeled off from the film surface by the pressure of the permeated water. As a result, clogging of the filtration membrane 15a is eliminated, and filtration resistance is reduced.

At this time, since the aqueous solution of sodium hypochlorite in the permeated water channel 15b is pushed out to the liquid to be treated by the permeated water, there is no possibility that the sodium hypochlorite is taken out as it is when filtration is resumed. Therefore, conventional operations such as returning the permeated water taken out at the beginning of the filtration restart to the flow rate control tank and injecting a reducing agent such as sodium sulfite to reduce chlorine are unnecessary.

If the total amount of sodium hypochlorite to be injected is large, it has a bad influence on microorganisms. Therefore, the amount is set to 5% or less, preferably 3% or less of the activated sludge dry weight. In addition, the above-mentioned sodium hypochlorite is effective for organic clogging substances, but an acid such as hydrochloric acid and nitric acid and an alkali such as sodium hydroxide are effective for inorganic clogging substances. An appropriate substance may be selected according to the kind of the substance, and these may be combined. As the water to be injected after the chemical, the above-described permeated water is economical, but it goes without saying that fresh water may be injected.

The above-described cleaning method can be similarly performed in a processing apparatus having a single aeration tank and a membrane separation device installed in the aeration tank. Further, the present invention can also be implemented by a membrane separation device in which ceramic membranes are arranged.

[0020]

As described above, according to the present invention, the reaction time between the chemical solution and the substance adhering to the film surface is secured, and water is fed after the chemical solution, so that the substance adhering to the film surface can be efficiently removed. The transmembrane pressure can be recovered by peeling, and the disposal of the chemical solution remaining on the permeation side of the filtration membrane can be eliminated.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a nitrification tank provided with a membrane separation device to be washed in one embodiment of the present invention.

FIG. 2 is a flowchart illustrating a conventional sewage treatment.

FIG. 3 is a partially cutaway perspective view of a conventional membrane separation device to be cleaned in one embodiment of the present invention.

[Explanation of symbols]

 5 Nitrification tank 7 Membrane separator 15 Membrane cartridge 15a Filtration membrane 15b Permeated water flow path 20 Washing pipe 22 Activated sludge mixture

Claims (2)

[Claims] 1. A method for cleaning an immersion type membrane separation device which is installed inside an aeration tank and filters an activated sludge mixture in the tank, wherein a substance adhering to a membrane surface is introduced into a permeated water flow path of the membrane separation device. Injecting the chemical solution to be decomposed and permeating the filtration membrane, maintaining the state in which the chemical solution in the permeated water flow path is in contact with the filtration membrane for 1 to 2 hours, and then washing the permeated water flow path with an approximately equal amount of the chemical A method for cleaning a membrane separation device, comprising injecting water and permeating a filtration membrane. 2. A chemical solution of 3 to 4 L per 1 m ^{2 of a} filtration membrane,
The method for cleaning a membrane separation device according to claim 1, wherein the injection is performed at a flux higher than the flux of the permeated water during the filtration operation.