JP2002126732A - Filtering system and filtering operation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filtering operation method not generating the closure of a filtrate line by air bubbles. SOLUTION: When filtering operation is performed by supplying raw water to a filter membrane module 12 from a raw tank 10, air bubbles in the piping of the filtrate line 36 are collected by an air trap 40 to prevent the clogging of the piping with air bubbles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtration system and a filtration operation method using the same, and more particularly, to a filtration system suitable for performing filtration by forming a dynamic membrane and a filtration operation method using the same.

[0002]

2. Description of the Related Art A biological treatment solution treated by applying an activated sludge method or the like still contains a large amount of suspended solid (SS), so that a non-woven fabric, a net, etc. is used as a membrane. The removal process of SS is performed by filtration using.

[0003] In the case of such a filtration using a nonwoven fabric or a net, the aperture is larger than that of a microfilter or the like. Therefore, so-called dynamic filtration is used to increase the removal rate of SS. This dynamic filtration is performed by using SS or floc (S
(Agglomerates of S) are deposited to form a dynamic membrane, and therefore, a method for promoting the formation of a dynamic membrane by slowing the supply rate of raw water is preferable.

[0004] Therefore, when dynamic filtration is applied, a method of slowing down the feed rate of raw water is adopted. However, when head difference filtration is used, the feed rate of the filtrate line after filtration is inevitably increased. Needs to be slowed down in relation to the feed rate of raw water.

[0005] However, when such a filtration operation is performed, if air enters the filtrate line, the piping may be blocked by air bubbles, in which case the filtration operation must be stopped. Repeatedly, the operation efficiency decreases. Furthermore, if a pump for air release is separately installed for air release, head filtration is performed. Therefore, when air is released, the filtration operation must be stopped.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a filtration system and a filtration operation method using the same, which can prevent an operation stop due to air being mixed into the piping of a filtrate line when performing filtration using a head difference. I do.

[0007]

According to the present invention, at least a raw water tank, a filtration membrane module in which a membrane element is immersed in an open-to-atmosphere housing, and a filtrate tank for storing filtrate are provided as means for solving the above problems. Provided is a filtration system including an air trap having an exhaust means in the middle of a filtrate line from a filtration membrane module to a filtrate tank.

The exhaust means in the present invention is, for example, an exhaust valve, and does not include a mechanical suction means such as a pump. By using an air trap having an exhaust means other than a mechanical suction means such as a pump, air in the filtrate can be removed without installing a separate pump or the like for removing air, and the head difference is utilized. It is possible to prevent the filtrate line piping from being clogged with air bubbles during the filtration operation.

[0009] In the filtration system of the present invention, the membrane used in the membrane element is preferably a nonwoven fabric or a net.

[0010] The present invention is also a filtration operation method using the above-mentioned filtration system, wherein raw water is supplied from a raw water tank to a filtration membrane module using a pump, and air is supplied to a filtration line from the filtration membrane module to the filtrate tank. Provided is a filtering operation method for trapping air bubbles by a trap.

[0011] In this manner, the filtration operation can be stably performed by collecting the air bubbles with the air trap.

[0012] In the filtration operation method of the present invention, it is preferable that the membrane element is mounted while being immersed in an open-to-atmosphere housing filled with fresh water. The fresh water used in this case is preferably tap water or a filtrate obtained by a filtration operation.

[0013] In this manner, the housing is filled with fresh water, and the membrane element is mounted by connecting the filtrate outlet of the membrane element and the piping of the filtrate line in a state where the membrane element is immersed. Air can be prevented from remaining in the air.

In the filtration operation method of the present invention, it is preferable that before the start of the filtration operation, the filtration membrane module is backwashed with the filtrate from the filtrate tank, and the air trapped in the air trap is exhausted by the exhaust means.

In this way, by performing the backwashing before the start of the filtration, air slightly remaining inside the membrane element can also be extracted.

The filtering operation method of the present invention uses a nonwoven fabric or a net, which has a large opening compared with a microfilter and easily mixes air, as a membrane, and forms a dynamic membrane on the membrane surface during the filtration operation. It is suitable.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a filtration system of the present invention and a filtration operation method using the same will be described with reference to FIG. FIG. 1 is a conceptual diagram of a filtration system used in the filtration operation method of the present invention.

The raw water tank 10 contains, for example, a processing liquid by the activated sludge method as raw water, and is sent from the raw water line 32 to the filtration membrane module 12 using a liquid feed pump.

The filtration membrane module 12 has a required number of membrane elements accommodated in an open-to-air housing having a required volume. The filtrate outlet of the membrane element is installed at a position lower than the water surface and penetrates the housing. , Filtrate line 3
6 are connected. As the membrane element, a non-woven fabric or a flat membrane element using a net is suitable.

The filtrate filtered by the filtration membrane module 12 passes through the filtrate line 36 and is sent to the filtrate tank 14 to be stored therein. However, in the middle of the piping of the filtrate line 36, a mechanical suction means such as a pump is used. An air trap 40 with no exhaust valve 43 is provided.

The structure of the air trap 40 is not particularly limited as long as it can trap air bubbles in the filtrate. For example, the air trap 40 may have a tubular shape or a tank shape as shown in FIG. Can be used.

The air trap 40 shown in FIG.
1 and a branch pipe 42 divided diagonally upward from the middle of the main pipe 41
And is connected to the middle of the filtrate line 36 at both ends of the opening of the main pipe 41. The end of the branch pipe 42 is normally closed by an exhaust valve 43,
Reference numerals 5, 46 and 47 indicate joints, and the arrows in the figure indicate the flow direction of the filtrate or the air bubbles.

In the air trap 40, the main pipe 41
Inside, a flow of the filtrate is generated in the direction of the arrow, and air bubbles rise in the direction of the arrow in the branch pipe 42. Therefore, air bubbles in the filtrate flowing through the pipe of the filtrate line 36 and reaching the main pipe 41 of the air trap 40 are collected at the upper end of the branch pipe 42. Branch pipe 4
The air collected in 2 is pushed out to the filtrate by a head difference and is discharged by opening the exhaust valve 43 as appropriate.
Accordingly, it is possible to prevent a situation in which air bubbles accumulate in the pipe of the filtrate line 36 and the pipe is blocked.

In another embodiment, the membrane element may be mounted by connecting the filtrate outlet of the membrane element and the piping of the filtrate line 36 in a state where the membrane element is immersed in fresh water in the housing. it can. At this time, after the housing is filled with fresh water, the membrane element may be immersed, or after housing the membrane element in the housing, fresh water may be injected until the membrane element is immersed.

When the membrane element is immersed in fresh water, the air inside the membrane element is pushed out, so that no or almost no air remains inside the membrane element. Therefore, it is possible to reduce the possibility that air is mixed into the filtrate and the piping of the filtrate line 36 is blocked.

As another embodiment, the filtrate outlet of the membrane element is connected to the pipe of the filtrate line 36 as in the above embodiment, and then backwashing is performed before the filtration is started. To collect air in the filtrate. The backwashing is performed by operating the backwashing pump 22 to send the filtrate in the filtrate tank 14 from the backwashing line 38 to the backwashing tank 16, from which the filtrate is pressed into the inside of the membrane element with a difference in gravity.

[0027] In this way, the air remaining in the membrane element slightly can be removed, so that the possibility that air enters the filtrate and the filtrate line 36 is blocked can be further reduced.

The membrane used as the membrane element in the present invention is preferably a nonwoven fabric or a net. In the present invention, the aperture, porosity, thickness, and the like of the nonwoven fabric and the net are not particularly limited.

The non-woven fabric may be made of various natural and synthetic resins, and the net may be made of metal such as stainless steel in addition to those made of natural and synthetic resins.

The above-described filtration operation method of the present invention is particularly suitable for a filtration operation in which a dynamic membrane is formed on the membrane surface during the filtration operation.

The filtering operation method of the present invention is applicable to treatment of biological treatment liquid containing activated sludge in a sewage treatment plant, treatment of wastewater from various facilities and domestic wastewater, and purification treatment of rivers, lakes and marshes. can do.

[0032]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 Using the filtration system shown in FIGS. 1 and 2, raw water is supplied from a raw water tank to a filter membrane module which is open to the atmosphere by a liquid feed pump, and excess water is returned to the raw water tank by overflow. To perform a filtration operation. Filtration was performed by head difference. The filtration operation is performed by the filtration membrane module 12.
After the membrane element is housed in the housing, the filtrate is injected until the membrane element is immersed, and the filtrate outlet of the membrane element is connected to the piping of the filtrate line 36. Air in the filtrate was collected by the air trap 40 in the line 36. After exhausting the air by opening the exhaust valve, the filtration operation was started. The filtrate line 36 had an inner diameter of 1 cm. As a result, even after a lapse of 10 minutes, the piping of the filtrate line 36 was not blocked, and there was no problem in continuing the operation.

Comparative Example 1 A filtration operation was performed in the same manner as in Example 1 except that the air trap 40 shown in FIG. 2 was not used. As a result, about 3 minutes after the start of operation, the piping of the filtrate line 36 is closed,
Driving could not be continued.

[0035]

According to the filtration operation method using the filtration system of the present invention, since the piping of the filtrate line is not blocked by air bubbles, the membrane filtration operation utilizing the head difference can be stabilized for a long time. Can be done. The filtration operation method of the present invention is particularly suitable for a filtration operation for forming a dynamic membrane using a nonwoven fabric or a net.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram for explaining a filtration system of the present invention.

FIG. 2 is a schematic sectional view of an air trap used in the filtration system of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 69/14 B01D 69/14

Claims (6)

[Claims] 1. A filtration system comprising at least a raw water tank, a filtration membrane module in which a membrane element is immersed in an open-to-air housing, and a filtrate tank for storing a filtrate, wherein a filtrate from the filtration membrane module to the filtrate tank is provided. A filtration system including an air trap having an exhaust means in the middle of a line pipe. 2. The filtration system according to claim 1, wherein the membrane used in the membrane element is a nonwoven fabric or a net. 3. A filtration operation method using the filtration system according to claim 1, wherein the filtration is performed using a head difference in a filtration membrane module, and an air trap is provided in a filtrate line from the filtration membrane module to a filtrate tank. A filtration operation method for collecting air bubbles. 4. The method according to claim 3, wherein the membrane element is mounted while being immersed in an open-to-air housing filled with fresh water. 5. The filtering operation according to claim 3, wherein the filtration membrane module is backwashed with the filtrate from the filtrate tank before starting the filtration operation, and the air trapped in the air trap is exhausted by the exhaust means. Method. 6. The filtration operation method according to claim 3, wherein a dynamic film is formed on the membrane surface during the filtration operation.