JPH0929074A - Liquid separation treatment method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently reduce the frequency of off-line washing by increasing the washing (back pressure washing) efficiency by the revolving flow of the liquid to be treated in a tank when a liquid is subjected to separation treatment by immersing a membrane separation module in an open type raw liquid tank and reducing the pressure in the membrane separation module on the side of the transmitted liquid passage thereof while washing the membrane surface with the revolving flow of the liquid to be treated in the tank. SOLUTION: In a method wherein a liquid to be treated is subjected to separation treatment by immersing a membrane separation module 2 in a tank of the liquid to be treated and reducing the pressure to the membrane separation module 2 on the side of the transmitted liquid passage thereof while washing the membrane surface of the membrane separation module 2 by the revolving flow of the liquid to be treated, the pressure reduction on the side of the transmitted liquid passage of the module by a suction pump 3 is intermittently performed and back pressure is allowed to act an the membrane surface of the module 2 by a transmitted liquid high peace storage tank 4 while washing is continued during a non-pressure reduction period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane separation module, which is immersed in an open type stock solution tank to wash the membrane surface of the membrane separation module with a swirling flow of a liquid to be treated in the tank. The present invention relates to a liquid separation processing method and device used when a liquid is separated and processed by depressurizing the permeated liquid passage side of the liquid.

[0002]

2. Description of the Related Art Membrane methods are sometimes used to separate suspended water. In this membrane method, it is essential to apply a transmembrane pressure between the raw solution side and the permeated side, and there are a method of pressurizing the raw solution side and a method of depressurizing the permeate side. Thus, the applicant of the present invention describes, as a permeate-side depressurization type membrane separator, "a membrane separator having an air diffuser and having a vertical passage along the membrane surface is provided directly above the air diffuser. Which has been provided with a means for making a negative pressure on the permeate side of the membrane device of the membrane device "(Japanese Patent Publication No. 4-709).
No. 58).

In order to treat sewage using this diffuser type aeration tank, the stock solution in the tank is swirled by the air-lift effect of the bubbles ejected from the diffuser, and along the membrane surface of the membrane separation module. The sludge gel layer is prevented from being generated on the membrane surface by the gas-liquid mixed upflow, and the permeate side of the membrane separation module is decompressed to generate the transmembrane pressure difference. Water is separated by permeation (hereinafter referred to as a membrane sewage treatment method). According to this membrane sewage treatment method, it is possible to reduce the size of the apparatus without requiring a precipitation separation tank.

[0004]

In the separation treatment of suspended water by membrane separation, since membrane contamination progresses with time and the permeation flux decreases, the permeation flux drops to a predetermined limit value. Then, it is necessary to interrupt the permeation / separation and wash the membrane to restore the permeation flux. In the above membrane sewage treatment method, the membrane surface is cleaned by the gas-liquid mixed flow even during the permeation / separation (in-line cleaning), so the membrane surface contamination speed can be reduced and the membrane permeation / separation is interrupted. The frequency of cleaning (offline cleaning) can be reduced. However, eventually, the permeation flux reaches a predetermined limit value, and at that time, the permeation / separation by reducing the pressure of the membrane separation module is interrupted,
It is necessary to pull up the membrane separation module from the stock solution tank and perform high-pressure water jetting on the membrane surface, cleaning with a sponge, and chemical solution immersion cleaning (offline cleaning). This off-line cleaning is cumbersome and inevitably costly, so it is required to be as infrequent as possible.

The object of the present invention is to immerse a membrane separation module in an open type stock solution tank and wash the membrane surface of the membrane separation module with a swirling flow of the liquid to be treated in the tank while the membrane separation module is being washed. When the liquid is separated by depressurizing the permeate passage side of the liquid, the liquid separation treatment method capable of sufficiently reducing the frequency of the above-mentioned off-line washing by improving the efficiency of the washing (in-line washing) by the swirling flow of the liquid to be treated in the tank, To provide a device.

[0006]

According to the method for separating liquid of the present invention, a membrane separation module is immersed in a liquid tank to be treated, and the membrane surface of the membrane module is washed by swirling the liquid to be treated. In the method of depressurizing the permeate passage side of the membrane separation module while separating the liquid to be treated, the permeate passage side of the module is intermittently depressurized, and the above washing is continued in the non-depressurized period. At the same time, a reverse pressure is applied to the membrane surface of the module by the stored water permeate. A liquid separation treatment apparatus according to the present invention comprises a membrane separation module arranged in a treatment tank, an air diffusing means arranged below the membrane separation module, and a permeated liquid of the membrane separation module. Between the suction pump that depressurizes the passage side, the permeate high-altitude reservoir that stores the permeate that has been sucked by the suction pump through the riser pipe, and the permeate reservoir and the permeate passage side of the membrane separation module. It is characterized in that it is provided with a communication pipe having a valve for communicating and blocking, and it is preferable that the height difference between the membrane separation module and the permeate high-altitude water storage tank is within 5 m.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing an example of a liquid separation processing apparatus according to the present invention. In FIG. 1, 1
Is an open type liquid tank to be treated. Reference numeral 2 denotes a flat membrane separation module in which flat membranes 21 having permeate passages are arranged side by side, and a raw liquid passage is secured between the flat membranes. One or both ends of each flat membrane are provided. Although a permeate collection tube is attached, this permeate collection tube is not shown.

Reference numeral 31 is a permeated water take-out pipe communicating with the permeated liquid collecting pipes of the flat membranes 21 ,. Reference numeral 3 denotes a suction pump provided in the pipe 31, which is provided with a control circuit 30 for intermittent driving. Reference numeral 32 is a valve provided on the inlet side of the suction pump 3. 41 is a rising pipe, 4 is a permeate high-altitude water storage tank provided at the upper end of the rising pipe 41, 42 is an overflow pipe of the permeate high-altitude water storage tank 4, and 5 is a membrane separation from the permeate high-altitude water storage tank 4. A communication pipe that allows communication with the permeate side of the module 2 and a valve 52 provided in the communication pipe 5. By the control circuit 30, in response to the intermittent drive of the suction pump 3, the valve 32 is opened and the valve 52 is closed while the operation of the suction pump 3 is on, and the valve 32 is closed while the operation of the suction pump 3 is off. At the same time, the valve 52 is opened. Reference numeral 61 is a stock solution supply pipe, and 62 is a liquid feed pump provided in the pipe 61. Denoted at 7 are air diffusers arranged directly below the flat membrane separation module 2. Reference numeral 71 is a blower connected to the air diffusers 7, .... Reference numeral 8 denotes a surplus sludge discharge pipe connected to the bottom of the liquid tank 1 to be treated.

In order to treat suspended water such as domestic wastewater and factory wastewater by the liquid separation and treatment method according to the present invention, this wastewater is temporarily stored in a storage tank, and in FIG. 62 is supplied to the liquid tank 1 to be treated, air is jetted from the diffuser pipes 7, ... By driving the blower 71, the jetted air current swirls the wastewater in the tank, and the suction pump 3 is intermittently driven to cause flat membrane separation. Module 2
The permeated liquid passage side is intermittently decompressed, and the organic matter in the wastewater is adsorbed and metabolized by aerobic microorganisms in contact with air to reduce the organic matter and to grow the aerobic microorganisms. Water is permeated through the permeate on the permeate side of the permeate 2 under the pressure difference across the membrane, and the permeate is temporarily stored in the permeate reservoir 4 via the rising pipe 41, and the overflow is performed.
Take out from the pipe 42. The surplus amount of the propagated aerobic microorganisms, that is, the activated sludge is discharged from the surplus sludge discharge pipe 8 to keep the activated sludge concentration at a constant high concentration.

When the suction pump 3 is stopped, the decompression is not performed and therefore the permeation is not performed, but the blower 71 is continuously driven and the swirling of the dirty water in the tank by the jet air from the diffuser pipes 7 is continued. Then, the valve 52 is opened to apply the permeate pressure of the head pressure based on the height difference of the rising pipe 41 to the permeate passage side of the membrane separation module 2, and thereafter, the suction pump 3 is restarted and stopped again. By repeating, the permeation of the permeate side passage of the membrane separation module 2 by the decompression and the permeate of the permeate side passage of the membrane separation module 2 by the head pressure are repeated.

In the above description, the pressure outside the flat membrane 21 is about 1 atm, and when the height difference between the membrane separation module 2 and the permeate water storage layer 4 is h, the valve 52 is stopped when the suction pump 3 is stopped. The pressure acting on the flat membrane of the flat membrane separation module 2 from the permeate side to the raw solution side by the open circuit is hρg / cm ² (ρ is the specific gravity of the permeate), and the height h is too high. Since expansion and destruction of the membrane adhesion part is caused, its height h is 5
It is safe to set it to m or less. In the above description, if the stop period of the intermittent drive suction pump 3 is T, the time t ₁ required to close the valve 32 during this period T and the time t required to open the valve 52 when the suction pump is re-driven. _{2, the} period T _{0 in} which the permeate side of the membrane separation module is pressurized by the head pressure of the permeate storage tank on the high side is
T is a _{0 = T-t 1 -t 2} .

In the above, when the suction pump 3 is driven, the valve 32 is opened, and the permeate side passage of the membrane separation module 2 is depressurized to generate the transmembrane pressure difference. The permeated liquid is temporarily stored in the permeated liquid water storage tank 4 and flows out from the overflow pipe 42. When the suction pump 3 is driven, the outer surface of the membrane of the membrane separation module 2 is in a suction state due to the reduced pressure on the permeate side of the module 2.
Therefore, when the suction pump 3 is stopped, the membrane surface is made to be in a discharge state opposite to the suction state by pressurization by the head pressure of the permeate in the water reservoir 4 on the permeate side of the module 2, The adherence and retention of the gel layer on the surface becomes unstable, and the gas-liquid mixed flow due to the jet flow from the diffuser tubes 7, ...
The gel layer can be effectively peeled off (back pressure washing).

Even if the gel layer is removed by back pressure washing when the suction pump is stopped, the stop time of the suction pump is considerably shorter than the driving time of the suction pump in order to secure the flow rate of the permeate or the separation speed. Therefore, the permeation flux eventually reaches a predetermined lower limit value while the permeation separation by the intermittent drive of the suction pump and the back pressure washing are repeated.
When this state is reached, the membrane separation module 2 is pulled up from the inside of the liquid tank 1 to be treated, high-pressure water jetting of the membrane surface, cleaning with a sponge and chemical solution immersion cleaning (offline cleaning) are performed, and the permeation flux is almost the initial value. After that, the permeation separation by the intermittent drive of the suction pump, the alternating operation of the back pressure cleaning, and the off-line cleaning are repeated. In the liquid separation treatment method according to the present invention, due to the above-mentioned back pressure cleaning, the membrane fouling speed (permeation flux reduction speed) is higher than the conventional example in which back pressure cleaning is not performed (suction pump is intermittently driven). Can be made sufficiently slow and the frequency of off-line cleaning can be reduced. This effect is
It can be confirmed by comparing the following examples and comparative examples. In the liquid separation treatment method according to the present invention, it is possible to swirl the stock solution with a pump instead of swirling the stock solution by air-jetting of the air diffusing tube.

[0014]

【Example】

[Embodiment] In FIG. 1, the flat membrane separation module 2 has 15 flat membranes having a membrane area of 0.3 m ² and a mutual spacing of 12 m.
Use a tank that has been made to be m, and use this as an effective volume of 0.4
It was arranged in the liquid tank 1 to be treated of m ³ . As the stock solution, an activated sludge mixed solution having an SS concentration of 15000 mg / liter was prepared and used, the aeration amount of the air diffusers 7, ... Was set to 100 liter / min, and the module 2 of the permeate storage tank 4 was used as a reference. The height h was set to 2 m. The suction pump 3 is intermittently driven with one cycle of suction for 8 minutes and stop for 2 minutes, and the valve 52 is opened for 1 minute while the suction pump is stopped for 2 minutes to set the head pressure of the permeate storage tank 4 (0.2 kg / cm ² ) Was made to act on the permeate side of the membrane separation module 2 (back pressure washing was performed). Suction pump 3
During suction, the rotation speed (suction pressure) of the suction pump was adjusted so that the permeation flow rate was maintained at 0.5 m ³ / m ² · day, and the suction pressure was measured with respect to the elapsed operating time.
It is as shown by the curve a in Fig. 2, and the suction pressure is -0.35kg.
/ Cm ² was reached and offline cleaning was performed.

[Comparative Example] In contrast to the example, the suction pump was intermittently driven, back pressure washing was not performed, and the permeation flow rate was 0.5 m ^3.
The rotation speed (suction pressure) of the suction pump was adjusted so that the suction pressure was maintained at / m ² · day, and the suction pressure with respect to the elapsed operating time was measured. Off-line cleaning was performed when the pressure reached 0.35 kg / cm ² . As is clear from the comparison between the curves a and b in FIG. 2, it is clear that the frequency of off-line cleaning can be sufficiently shortened (about half) as compared with the conventional example according to the present invention.

[0016]

According to the present invention, the membrane separation module is immersed in the liquid tank to be treated and the membrane surface of the membrane module is washed by swirling the liquid to be treated while the membrane separation module of the membrane separation module is being washed. When decompressing the permeate passage side to separate the liquid to be treated, it is possible to sufficiently reduce the frequency of the troublesome off-line cleaning performed by taking the membrane separation module out of the tank, and the fear of back pressure damage of the membrane. Nor. Therefore, the present invention is directed to the operation of the membrane separation module.
It is extremely useful for simplifying management or maintenance.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a liquid separation processing apparatus according to the present invention.

FIG. 2 is a diagram showing a permeation state in an example and a comparative example of a liquid separation process according to the present invention.

[Explanation of symbols]

 1 treated liquid tank 2 membrane separation module 3 suction pump 4 permeate storage tank 5 communication pipe 52 valve 7 diffuser pipe

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 31, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 2

[Correction method] Change

[Correction contents]

Claims (3)

[Claims] 1. A membrane separation module is immersed in a treatment liquid tank, and the permeate passage side of the membrane separation module is depressurized while cleaning the membrane surface of the treatment liquid by swirling the treatment liquid. In the method of separating the liquid to be treated, the pressure on the permeate passage side of the module is intermittently reduced, and while the washing is continued during the non-depressurized period, the reverse pressure of the stored permeate is applied to the membrane surface of the module. A method for separating and treating a liquid, which comprises: 2. A membrane separation module arranged in a treatment tank, an air diffusing means arranged below the membrane separation module, and a vacuum for decompressing the permeate passage side of the membrane separation module. The pump, the permeate aerial reservoir for storing the permeate sucked by the suction pump through the riser pipe, and the permeate aerial reservoir and the permeate passage side of the membrane separation module are connected and disconnected. And a communication pipe having a valve. 3. The liquid separation treatment apparatus according to claim 2, wherein the height difference between the membrane separation module and the permeate high-altitude water storage tank is within 5 m.