JPH08290045A - Method for washing of immersion type membrance cartridge - Google Patents

Abstract

PURPOSE: To decompose the contaminant of a boundary part and to easily and almost perfectly remove a cake layer by supplying a chemical soln. to transmitted water under low pressure to hold the same in such a state that a membrane cartridge is immersed in a liquid to be treated and filtering/aeration is stopped to perform aeration from below. CONSTITUTION: A membrane cartridge 17 is immersed in an activated sludge mixed liquid 13 and, in such a state that a blower 18 and a suction pump 23 are stopped to stop aeration and filtering, the chemical soln. in a chemical soln. tank 25 is allowed to flow down naturally to be injected into the transmitted water passage of the membrane cartridge 17 to be held therein. The blower 18 is driven before filtering operation is resumed to supply aeration air to the membrane cartridge 17 from below through an air diffusion pipe 19. Whereupon, the cake layer bonded to the membrane surface of the membrane cartridge 17 is almost perfectly peeled to be washed off. The chemical soln. used herein is oxalic acid (5000-10000mg/l) or sodium hypochlorite (effective chlorine concn.; about 0.5-17).

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 submerged membrane cartridge used for solid-liquid separation in activated sludge treatment of organic wastewater, sludge flocculation treatment and the like.

[0002]

2. Description of the Related Art Conventionally, in facilities that perform activated sludge treatment or sludge flocculation treatment of organic waste water, as a solid-liquid separation device for separating activated sludge or flocculated sludge, for example, it is immersed in a liquid to be treated in a treatment tank. A submerged membrane separator is installed. The immersion type membrane separation device is as shown in FIG. 2, in which a flat plate-shaped membrane cartridge 2 arranged vertically is arranged in parallel in a box-shaped casing 1 having an opening at the top and the bottom to form a membrane. Below the cartridge 2, an air diffuser 3 connected to an air supply means (not shown) such as a blower is arranged. In the membrane cartridge 2, the organic filtration membranes 5 and 5 are arranged on both sides of the membrane support 4, and the surface and the inside of the membrane support 4 covered with the filtration membrane 5 serve as a permeate flow channel 6. The passage 6 communicates with a suction means (not shown).

When solid-liquid separation is carried out, a suction pressure is applied to the permeate flow path 6 of the membrane cartridge 2 by a suction means so that suspended substances such as activated sludge are captured by the filtration membrane 5, and the filtration membrane is filtered. The permeated water that has passed through 5 and flowed into the permeated water channel 6 is taken out. At this time, aeration air is supplied through the air diffuser 3, and the surface of the filtration membrane 5 is cleaned by the bubbles of the aeration air and the upward flow of the liquid to be treated caused by the air lift action of the bubbles.

[0004]

However, in the membrane cartridge 2 as described above, solid-liquid separation can be performed without applying a large suction pressure, so that energy saving can be achieved, but on the other hand, chemical cleaning can be performed for various reasons such as a rapid change in concentration. When it becomes necessary, it is difficult to clean because it is immersed in the liquid to be treated.

Therefore, a method of taking out the whole of the immersion type membrane separation device (hereinafter referred to as a membrane separation device) from the treatment tank and immersing it in the chemical cleaning tank, or after discharging all the liquid to be treated in the treatment tank, Although a method of filling a chemical solution has been proposed, all of them require a large-scale device and are not economical. Moreover, such an outside of the filtration membrane (processing liquid side)
Since it is difficult to remove dirt such as sludge adhered to the surface of the filtration membrane in the chemical cleaning from the above, it is also necessary to perform physical cleaning with a sponge or the like.

A cleaning method has also been proposed in which a gas, permeated water, or a chemical solution is injected at high pressure into the inside of a filtration membrane (permeate flow path) in a state in which a membrane cartridge is immersed in a liquid to be treated. In the cleaning method, the gas and the like flow out from the inside to the outside of the filtration membrane where the dirt is relatively light or where the gas easily flows. There is a problem in strength such as peeling.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a cleaning method capable of easily and effectively cleaning an immersion type membrane cartridge.

[0008]

In order to solve the above-mentioned problems, a method for cleaning an immersion type membrane cartridge of the present invention is a method in which the immersion type membrane cartridge is immersed in a liquid to be treated and filtration and aeration are stopped. Injecting a chemical solution into the permeate flow path of the membrane cartridge at low pressure and holding it for an appropriate period of time, and before restarting filtration, supply aeration air from below the membrane cartridge for an appropriate period of time to remove the deposits on the membrane surface. It was done.

[0009]

According to the above construction, the chemical liquid is supplied to the permeate side at a low pressure and held for an appropriate period of time while the pressures on the treated liquid side and the permeated water side maintain a constant balance across the filtration membrane. Therefore, the chemical liquid leaches out to the liquid to be treated more uniformly than the entire membrane surface of the filtration membrane. Then, to the place where the fouling substances at the boundary between the cake layer attached to the membrane surface and the filtration membrane are decomposed and the cake layer is easily peeled off, aeration air is supplied from below for an appropriate time, so the cake layer Easily and almost completely removed.

[0010]

Embodiments of the present invention will be described below. (Example 1) In FIG. 1, 11 is an activated sludge tank,
Inside the activated sludge tank 11, an activated sludge mixed solution 13 obtained by mixing activated water with raw water introduced from a raw water supply pipe 12
Is stored and is immersed in the activated sludge mixed liquid 13 to install the membrane separator 14. Reference numeral 15 is a sludge drawing pipe.

In the membrane separation device 14, flat plate-shaped membrane cartridges 16 arranged in the vertical direction are installed in parallel inside a box-shaped casing 16 opened at the top and bottom at appropriate intervals, and below the membrane cartridge 17. It is configured by installing an air diffuser 19 connected to the blower 18.

The membrane cartridge 17 is constructed in the same manner as the conventional one described with reference to FIG. 2, and is provided with a suction pipe 20 which communicates with the permeate passage inside the filtration membrane. The suction pipe 20 communicates with a permeate water pipe 24 in which a switching valve 22 and a suction pump 23 are arranged via a header pipe 21, and the chemical liquid tank 2 storing the chemical liquid via the switching valve 22.
5. The tank communicates with a fresh water tank 26 that stores fresh water.

In the activated sludge tank 11 as described above,
Immerse the membrane cartridge 17 in the activated sludge mixed solution 13,
With the blower 18 and the suction pump 23 stopped to stop aeration and filtration, sodium hypochlorite (effective chlorine concentration of about 0.5 to 1%) in the chemical liquid tank 25 is placed in the permeate passage of the membrane cartridge 17. Was poured under gravity flow and held for 1-2 hours.

Before restarting the filtration operation, the blower 18 is driven to drive the membrane cartridge 17 through the air diffuser 19.
Aeration air was supplied from below for 10 to 30 minutes. In addition,
If necessary, fresh water in the fresh water tank 26 is naturally flown into the permeate flow path of the membrane cartridge 17 in an amount of 1 to 3 times the volume of the sodium hypochlorite solution to allow hypochlorous acid in the permeate flow path. The soda solution was extruded to the activated sludge mixed solution 13 side.

As a result of washing in this manner, the cake layer adhering to the membrane surface of the membrane cartridge 17 was almost completely peeled off and the membrane pores were well washed. This is because, while the sodium hypochlorite solution is supplied at a low pressure into the permeated water flow path of the membrane cartridge 17 in the immersed state and kept for a proper time, the fouling substances on the surfaces inside and outside the filtration membrane and in the pores are decomposed. This is because the cake layer, which is easily peeled off by this, is physically removed by the aerated air. In this example, since the fouling substance is mainly organic matter such as activated sludge, sodium hypochlorite was used as the chemical liquid, but other oxidizing agents may be used. (Example 2) The membrane cartridge was washed in a coagulation tank in which a coagulation mixed liquid prepared by mixing raw water with a coagulant was stored. The configurations of the flocculation tank, the membrane separation device, and the devices associated therewith are substantially the same as those described in Embodiment 1 with reference to FIG.

Oxalic acid as a liquid medicine (5000 to 10,000 mg / L)
As a result of washing in the same manner as in Example 1 except that this oxalic acid was held in the permeated water flow path of the membrane cartridge for 30 minutes to 1 hour, most of the cake layer adhered to the membrane surface of the membrane cartridge was peeled off. The membrane pores were also washed well. In this embodiment, oxalic acid was used because the fouling substance is mainly iron-based or aluminum-based floc, but other acids such as hydrochloric acid and nitric acid may be used.

In the above-mentioned embodiment, the membrane separation apparatus for exercising the solid-liquid separation by using the suction pressure of the suction pump as the driving force has been exemplified. The membrane cartridge can be washed in the same manner in the membrane separation apparatus that performs the above. Further, the membrane cartridge is not limited to the one described above, and if the inner side of the filtration membrane is used as the permeate flow channel, the membrane cartridge can be washed in the same manner, such as one having only the surface of the membrane support as the permeate flow channel.

[0018]

As described above, according to the present invention, while the membrane cartridge is immersed in the liquid to be treated and filtration and aeration are stopped, the chemical liquid is supplied to the permeate side at a low pressure and is held for an appropriate time. As a result, the fouling substance at the boundary with the filtration membrane is decomposed, and the cake layer that is more easily peeled off from the membrane surface is peeled off by the aerated air. Therefore, the cake layer can be almost completely removed. Therefore, it is possible to easily and effectively wash the membrane cartridge without requiring a large-scale device and breaking the filtration membrane unlike the conventional case.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a schematic configuration of an activated sludge tank equipped with a membrane separation device to which a cleaning method for an immersion type membrane cartridge of the present invention is applied.

FIG. 2 is an explanatory diagram showing a schematic configuration of a conventionally used membrane separation device.

[Explanation of symbols]

 13 Activated sludge mixture 14 Membrane separation device 17 Membrane cartridge 19 Air diffuser 25 Chemical tank

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Soeda 1-247 Shikitsuhigashi, Naniwa-ku, Osaka-shi, Osaka Kubota Corporation

Claims (1)

[Claims] 1. A submerged membrane cartridge is immersed in a liquid to be treated, and while filtration and aeration are stopped, a chemical liquid is injected into the permeate passage of the membrane cartridge at a low pressure, and the liquid is held for an appropriate period of time to restart the filtration. Prior to this, a cleaning method for an immersion type membrane cartridge, characterized in that aeration air is supplied from below the membrane cartridge for an appropriate period of time to remove the deposits on the membrane surface.