JP2004202443A - Membrane separation device - Google Patents

Abstract

Kind Code: A1 A membrane filtration density is high, membrane filtration can be performed with a high filtration driving force and a high membrane permeation flux, and the separation and cleaning efficiency of contaminants is excellent, and the membrane filtration is stable and efficient for a long time. To provide a submerged hollow fiber membrane separation device capable of performing
An immersion type hollow fiber membrane separation device using an internal pressure type hollow fiber membrane. The internal pressure type hollow fiber membrane module 3 is immersed in the permeated water tank 2, the raw water is pressurized and supplied by the raw water pump 4 into the hollow fiber membrane tube, the membrane is filtered, and the air is supplied from the blower 5 into the hollow fiber membrane. Air scrubbing is performed, and then backwashing is performed by extracting raw water from the hollow fiber membrane tube by the backwashing suction pump 6.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a submerged hollow fiber membrane separation device used for membrane filtration of service water or wastewater.
[0002]
[Prior art]
Hollow fiber membranes are one type of separation membrane used for membrane separation treatment. The hollow fiber membrane includes an internal pressure type hollow fiber membrane having a raw water flow path inside the tube of the hollow fiber membrane, and an external pressure type hollow fiber membrane having a raw water flow path outside the hollow fiber membrane.
[0003]
Further, as a membrane separation device using such a hollow fiber membrane, a pressure vessel type in which a hollow fiber membrane module is provided in a pressure vessel (filtration tower), and a hollow fiber membrane module immersed in a water tank are arranged. Of these, the pressure vessel type membrane separator requires a maintenance space and various pipes to be provided for each vessel, and separates the space for membrane filling from these additional facilities. Since a large space is required, there is a disadvantage that the packing density of the film is low. On the other hand, such a problem is solved in the immersion type membrane separation device.
[0004]
Conventionally, an external pressure type hollow fiber membrane is generally employed in an immersion type hollow fiber membrane separation device in which a hollow fiber membrane module is immersed in a liquid in a tank. This is because in an internal pressure type hollow fiber membrane in which raw water flows through the tube of the hollow fiber membrane, the raw water flow path is easily blocked due to suspended substances contained in the raw water, while the raw water flows through the outside of the hollow fiber membrane. This is because an external pressure type hollow fiber membrane that allows permeated water to pass through a tube of the hollow fiber membrane can solve such a problem of the flow path blockage.
[0005]
In an immersion type hollow fiber membrane separation device using an external pressure type hollow fiber membrane, a hollow fiber membrane module is immersed in a raw water tank, and the permeated water permeating the membrane is sucked out of the hollow fiber membrane tube by a suction pump and taken out. . A diffuser pipe is provided below the hollow fiber membrane module in the raw water tank to separate and clean contaminants attached to the outer surface of the membrane. It has a backwashing pressure pump for washing, and regularly performs backwash with permeated water and peeling and cleaning of contaminants by aeration.
[0006]
[Problems to be solved by the invention]
The immersion type hollow fiber membrane separation device using the external pressure type hollow fiber membrane has the following disadvantages.
[0007]
{Circle around (1)} The air from the air diffuser provided below the hollow fiber membrane module rises outside the hollow fiber membrane, so that all of the air does not act on the membrane surface, causing waste of air and peeling and cleaning. ineffective. That is, the amount of aeration for obtaining the necessary peel strength is large, and the power cost is high.
[0008]
{Circle around (2)} When the distance between adjacent hollow fiber membranes of the hollow fiber membrane module is small, suspended substances may be concentrated between the hollow fiber membranes and gelled or caked. Therefore, it is necessary to increase the distance between the hollow fiber membranes to some extent, which is one of the reasons why the packing density of the membrane cannot be increased.
[0009]
{Circle around (3)} Since the filtration driving force is obtained by sucking the permeated water side in the hollow fiber membrane, it is limited by the air pressure, so that the suction cannot be performed at a pressure of 1 atm or more, and the membrane permeation flux cannot be large. For this reason, in the immersion type hollow fiber membrane separation device using the external pressure type hollow fiber membrane, the permeation flux is very small as compared with the pressure vessel type membrane separation device.
[0010]
The present invention solves the above-mentioned conventional problems, can increase the membrane packing density, and can increase the filtration driving force to increase the membrane permeation flux. It is an object of the present invention to provide an immersion type hollow fiber membrane separation device having a good separation and cleaning efficiency.
[0011]
[Means for Solving the Problems]
The membrane separation device of the present invention is a membrane separation device that supplies raw water to a hollow fiber membrane module and obtains permeated water, wherein a permeated water storage tank that stores permeated water and a hollow water that is immersed and disposed in the permeated water storage tank are provided. It is characterized by comprising a fiber membrane module, a pressurizing pump for supplying raw water into a hollow fiber membrane tube constituting the hollow fiber membrane module, and a suction pump for extracting raw water from the hollow fiber membrane tube.
[0012]
Since the membrane separation apparatus of the present invention is an immersion type membrane separation apparatus, the membrane packing density can be increased as compared with a pressure vessel type membrane separation apparatus.
[0013]
In addition, as the hollow fiber membrane, an internal pressure type hollow fiber membrane that is immersed and arranged in a permeated water storage tank and feeds raw water into the tube of the hollow fiber membrane under pressure to take out permeated water from the outer surface of the membrane is used. The following effects are exhibited as compared with the immersion type membrane separation device using the external pressure type hollow fiber membrane.
[0014]
(1) Since air is directly injected into the hollow fiber membrane to perform peeling and cleaning, the entire amount of air flowing through the membrane acts on the primary (raw water) surface of the membrane. Air is not wasted, and the effect of removing contaminants by air is high. Therefore, the amount of air for obtaining the required peel strength is small (generally, about 1/2 of the external pressure type hollow fiber membrane is sufficient), and the power cost can be reduced.
[0015]
(2) Since the permeated water from which suspended substances are removed flows on the outer surface of the hollow fiber membrane, there is no problem of clogging between the hollow fiber membranes even if the interval between adjacent hollow fiber membranes is reduced. The film packing density can be increased. Generally, it is possible to set a large membrane packing density of 1200 m ² -membrane area / m ² -site or more.
[0016]
(3) Since the raw water is pressurized and supplied into the hollow fiber membrane tube by a pressure pump, the transmembrane pressure difference for obtaining the filtration driving force is not restricted by the atmospheric pressure, and the pressure can be filtered even at a pressure of 100 kPa or more. is there. For this reason, the membrane permeation flux can be increased, and practical filtration performance can be obtained with a permeation flux equivalent to that of a normal pressurized vessel system.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the membrane separation device of the present invention will be described in detail.
[0018]
FIG. 1 is a system diagram showing an embodiment of the membrane separation device of the present invention.
[0019]
1 is a raw water tank, 2 is a permeated water tank (permeated water storage tank), and the internal pressure type hollow fiber membrane module 3 is immersed in the permeated water tank 2. Raw water in the raw water tank 1 is supplied to the hollow fiber membrane tube of the internal pressure type hollow fiber membrane module 3 through the pipes 12 and 13 by the raw water pump 4 under pressure, and the permeated water passing through the hollow fiber membrane is transmitted to the permeated water tank. 2 and discharged out of the system from the pipe 15 as necessary. The concentrated water is circulated from the pipe 14 to the raw water tank 1.
[0020]
Reference numeral 5 denotes an air scrubbing blower. By this blower 5, scrubbing air is supplied from a pipe 16 into the hollow fiber membrane of the internal pressure type hollow fiber membrane module 3, and exhaust air is discharged from a pipe 17.
[0021]
Reference numeral 6 denotes a suction pump for backwashing. The pump 6 sucks raw water in the hollow fiber membrane of the internal pressure type hollow fiber membrane module 3 and extracts it from the pipes 13, 18, and 19, so that the hollow fiber membrane is backwashed. Done.
[0022]
11 raw water introduction _pipe, V 1 ~V ₅ is a closing valve.
[0023]
At the time of membrane filtration of the raw water, the valves V ₁ and V _{2 are} opened and the valves V _{3 to} V _{5 are} closed, and the raw water in the raw water tank 1 is added to the hollow fiber membrane tube of the internal pressure type hollow fiber membrane module 3 by the raw water pump 4. Supply pressure to obtain permeate.
[0024]
Such a membrane filtration operation causes contaminants to adhere to the primary side (raw water) side membrane surface (tube inner wall) of the hollow fiber membrane of the internal pressure type hollow fiber membrane module 3 and lowers the membrane permeation flux. In order to remove these contaminants, aeration cleaning (air scrubbing) and backwashing are performed.
[0025]
At the time of air scrubbing, the valves V ₃ and V _{4 are} opened and the valves V ₁ , V ₂ and V _{5 are} closed to supply air from the air scrubbing blower 5 into the hollow fiber membrane tube of the internal pressure type hollow fiber membrane module 3. Scrubbing is performed to remove contaminants adhering to the inner wall of the hollow fiber membrane tube. After that, the valves V ₁ , V _{5 are} opened and the valves V ₂ , V ₃ , V _{4 are} closed, and the backwater suction pump 6 suctions the inside of the hollow fiber membrane tube of the internal pressure type hollow fiber membrane module 3 to extract raw water. Are discharged from the pipes 13, 18, and 19. By extracting the raw water from the hollow fiber membrane tube, the permeated water in the permeate tank 2 flows back into the membrane tube from the outer surface (secondary side) of the hollow fiber membrane, and the membrane is backwashed. In addition, the backwash drainage may be discharged out of the system from the pipe 19 or may be returned to the raw water tank 1.
[0026]
As described above, by alternately performing the membrane filtration operation by the internal pressure type hollow fiber membrane module 3 and the washing operation of air scrubbing and backwashing, stable and efficient operation can be continued for a long time.
[0027]
In the membrane separation device of the present invention, a transmembrane pressure (filtration driving force) up to about 1000 kPa can be set by using an internal pressure type hollow fiber membrane module for supplying raw water into the hollow fiber membrane tube under pressure. . In addition, it is preferable that the transmembrane pressure is practically not more than about 300 kPa. Therefore, continuous operation can be performed without performing chemical cleaning until the transmembrane pressure rises to about 300 kPa.
[0028]
The frequency of the washing operation of air scrubbing and backwashing is appropriately determined according to the quality of the raw water to be treated, the specifications of the hollow fiber membrane to be used, and the like, but is usually about 10 to 300 minutes, preferably 20 to 300 minutes. Air scrubbing for about 0.1 to 10 minutes, preferably about 0.5 to 1 minute and backwashing for about 0.1 to 10 minutes, preferably about 0.5 to 1 minute for every 60 minutes of membrane filtration operation. It is preferable to carry out the cleaning operation described above. At the time of this cleaning operation, it is not always necessary to perform air scrubbing and backwashing, and only one of air scrubbing and backwashing may be performed. Further, a cleaning operation for performing air scrubbing and backwashing and a cleaning operation for only backwashing may be performed in an appropriate combination.
[0029]
There is no particular limitation on the membrane material, dimensions, etc. of the internal pressure type hollow fiber membrane module used in the present invention. In the present invention, by employing the internal pressure type hollow fiber membrane module in the immersion type hollow fiber membrane separation device, the membrane packing density and the membrane permeation flux can be increased, and efficient membrane filtration and washing operations can be performed.
[0030]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0031]
Example 1
Using the membrane separation device of the present invention shown in FIG. 1, a test was performed using river water having a maximum turbidity of about 50 ° as raw water.
[0032]
The specifications of the internal pressure type hollow fiber membrane module used are as follows.
[0033]
[Hollow fiber membrane module]
Material: Hollow fiber made of polysulfone Dimensions: inner diameter 1.2 mm, outer diameter 1.9 mm
Film area: 2.8 m ²
Number of hollow fibers: 400
The operating conditions were as follows.
[0035]
[Operating conditions]
Membrane permeation flux: 1.5 m ³ / m ² / day
Backwashing, air scrubbing interval: Every 30 minutes (after air scrubbing for 1 minute, water backwashing for 1 minute)
Backwash flux: 1 m ³ / m ² / day
Air aeration amount: 0.012 Nm ³ / min (set so as to have a flow rate of 0.2 m / sec inside the hollow fiber)
Cross flow velocity: 0.2m / sec
[0036]
As a result, water flow was started at a transmembrane pressure of 5 kPa (25 ° C.), and the transmembrane pressure increased to 13 kPa after 30 days of continuous operation. The rate of increase in transmembrane pressure is 0.27 kPa / day, and if it can be increased to 250 kPa, it can be said that continuous water flow for about 2.5 years is possible.
[0037]
【The invention's effect】
As described in detail above, according to the membrane separation device of the present invention, the immersion type hollow fiber membrane separation device is constituted by the internal pressure type hollow fiber membrane module, so that the membrane packing density is high, the filtration driving force is high, and the membrane permeation is high. Provided is a submerged hollow fiber membrane separation device that can perform membrane filtration with a flux and has excellent exfoliation and cleaning efficiency of contaminants, and can perform stable and efficient membrane filtration over a long period of time.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of a membrane separation device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Permeated water tank 3 Internal pressure type hollow fiber membrane module 4 Raw water pump 5 Air scrubbing blower 6 Backwash suction pump

Claims (2)

In a membrane separation device that obtains permeated water by supplying raw water to a hollow fiber membrane module,
A permeated water storage tank for storing permeated water,
A hollow fiber membrane module immersed in the permeated water storage tank,
A pressure pump for supplying raw water into a hollow fiber membrane tube constituting the hollow fiber membrane module;
A membrane separation device comprising: a suction pump for extracting raw water from a tube of the hollow fiber membrane. 2. The membrane separation device according to claim 1, further comprising an air supply means for supplying air into the hollow fiber membrane tube.

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