JP3536558B2 - Immersion type membrane separation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane separation device in which a hollow fiber membrane element is immersed in a liquid in a tank.
The present invention relates to an immersion type membrane separation device suitable for membrane filtration of a suspension of activated sludge or coagulated sludge.

[0002]

2. Description of the Related Art Hollow fiber membranes are one type of separation membrane used for membrane separation. The hollow fiber membrane includes an internal pressure type hollow fiber membrane using the inside of the hollow fiber membrane as a raw water flow path, and an external pressure type hollow fiber membrane using the outside of the hollow fiber membrane as a raw water flow path.

[0003] The internal pressure type hollow fiber membrane has a drawback that the flow path of raw water is narrow and the raw water flow path is blocked in a short time, so that it is not suitable for filtering suspended substances. On the other hand, the external pressure type hollow fiber membrane solves this problem by passing raw water through the outside of the hollow fiber membrane and passing permeated water through the inside.

However, even in the external pressure type hollow fiber membrane, the suspended substance is concentrated between adjacent hollow fiber membranes, gelling or caked, and the effective area of the hollow fiber membrane is reduced. This is referred to as “flow path blockage.”

[0005] For this reason, various studies have been made on a module form or a module installation method that does not easily cause blockage of the transmembrane flow path. For example, as shown in FIG. 2A (front view) and FIG. 2B (plan view), a plurality of hollow fiber membranes 1
Are commercially available.

The hollow fiber membrane element 2 has a number of hollow fiber membranes 1 arranged in parallel so as to form a screen surface S, and both ends of the hollow fiber membrane 1 are buried and held in water collecting pipes 3 and 3, respectively. Things. The filtered water that has passed through the hollow fiber membrane 1 is taken out through the water collection pipes 3 and 3 and the extraction pipes 4 and 4.

In the case of filtering raw water using such a screen-shaped external pressure type hollow fiber membrane element as a module, a circulating flow is given to the membrane surface by aerating gas from below the module, thereby forming the hollow fiber membrane. Techniques for obtaining high flux by vibrating have also been developed.

Conventionally, the screen-shaped external pressure type hollow fiber membrane element 2 is immersed in a treatment tank in a state shown in FIG. 2 (a), and a raw water flow or a diffused gas is supplied from below, or as shown in FIG.
As shown in the figure, a plurality of the screens are stacked so as to be horizontal and immersed in a treatment tank in a modular state, and the raw water flow is set to an upward flow or a downward flow. This is because in this way the hollow fiber membrane is disposed across the raw water flow, not only raw water stream impinges on the perpendicular to the longitudinal direction of the bubble hollow fiber membrane 1 when performing aeration under side of the module , A high flux and a high film surface cleaning effect.

Although the screen-shaped external pressure type hollow fiber membrane element is unlikely to cause clogging of the intermembrane flow path, in the conventional membrane separation device provided so that the hollow fiber membrane crosses the raw water flow, the membrane flow rate is reduced. The effect of preventing road blockage is not sufficient. In particular, blockage of the intermembrane flow passage is likely to occur in portions other than the central portion of the hollow fiber membrane of the element. This cause is shown in FIGS.
This will be described with reference to FIG.

FIG. 4 is a schematic view of a screen-like external pressure type hollow fiber membrane element in which the hollow fiber membrane longitudinal direction crosses the raw water flow and the screen surface is parallel to the raw water flow. The horizontal axis indicates the extending direction of the hollow fiber membrane, and the vertical axis indicates the vertical displacement of the hollow fiber membrane.

As is apparent from FIG. 4, the angle .theta. Formed by the hollow fiber membrane with respect to the horizontal line increases as the distance from the water collecting pipe holding portion increases. Here, taking a small section Z where θ can be regarded as constant, as shown in an enlarged view in FIG. 5, the width L ′ of the hollow fiber bundle in the direction perpendicular to the hollow fiber membrane is equal to the width of the hollow fiber bundle in the water collecting tube holding part. L ′ = cos θ · L with respect to the width L. That is, in the cross section M ′ in the L ′ direction, the interval between the hollow fiber membranes is cos θ times larger than in the cross section M in the L direction, and the membrane packing density in the direction perpendicular to the hollow fiber membrane is 1 / cos θ.
Double. Here, since cos θ <1, the cross section M ′
In this case, the interval between the hollow fiber membranes becomes narrow. Therefore, in the conventional installation mode, as the hollow fiber membrane approaches the water collecting pipe holding portion, the hollow fiber membrane becomes dense and the raw water flow path is easily blocked.

It is conceivable to hold the hollow fiber membrane in a tensioned state, but it is not preferable to hold the hollow fiber membrane in a tensioned state because the hollow fiber membrane is likely to be damaged.

The cause will be described below with reference to FIGS.

FIG. 6 shows the ratio K / K _max between the distance K between the water collecting pipe holding portions at both ends of the hollow fiber membrane and the maximum distance, ie, the distance K _max when the hollow fiber membrane is held in the most tensioned state. FIG. 5 is a correlation diagram in which the horizontal axis represents the horizontal axis and the angle θ of the hollow fiber membrane in the vicinity of the water collecting tube holding section with respect to the horizontal line is the vertical axis. From FIG. 6, the larger the distance K between the water collecting pipe holding portions at both ends of the hollow fiber membrane, that is, the smaller the slack of the hollow fiber membrane, the smaller the angle θ becomes. It can be seen that the packing density at

However, when the distance K between the water collecting pipe holding portions at both ends of the hollow fiber membrane is increased, the tension applied to the hollow fiber membrane increases in proportion thereto. As is clear from FIG. 7, which shows the relationship between the distance between the water collecting tube holding parts at both ends of the hollow fiber membrane and the tension applied to the hollow fiber membrane, the distance K between the water collecting pipe holding parts at both ends of the hollow fiber membrane is the maximum value K. _As it approaches _max , the tension increases sharply. When the tension increases, the risk of breakage of the hollow fiber membrane and the breakage of the water collection tube holding portion of the hollow fiber membrane increases.

Japanese Patent Application Laid-Open No. 6-198144 discloses that in a membrane separation apparatus in which a plurality of flat membrane modules are immersed and arranged in parallel in a tank, the position of a water collecting pipe at the tip of the membrane is made different between adjacent modules. Is described.

[0017]

Even when the longitudinal direction of the hollow fiber membrane of the hollow fiber membrane module is arranged parallel to the raw water flow direction, as shown in FIG.
When the positions of the water collecting pipes 3 and 3 are the same in the raw water flow direction, the distance between the water collecting pipes 3 and 3 becomes small, and the raw water flowing through the water collecting pipes 3 and 3 and flowing between the elements 2 and 2 Is weakened, whereby the transmembrane flow path is easily blocked.

In the case of the flat membrane type membrane separation apparatus disclosed in JP-A-6-198144, elements in which a membrane is stretched on a plate-like support plate are integrated and modularized. Therefore, the portion where the liquid flows is between the films. From the viewpoint of increasing the membrane area, it is necessary to reduce the thickness of the support plate and reduce the flow path interval. However, the flow path interval is easy for the liquid to flow,
In turn, it must be kept large in terms of transmembrane occlusion.

Although the hollow fiber membrane element has a membrane area about twice that of a flat membrane element of the same scale, a water collecting pipe is provided at the end of the hollow fiber membrane, and this water collecting pipe hinders the flow of raw water. There is. That is, when this hollow fiber membrane element is installed (vertically placed) in the horizontal direction in the liquid flow direction, the water collecting pipe at the end of the membrane is located in the vertical direction of the tank. In the lower part of the tank, a water flow is generated with the air from the air diffuser, creating an upward flow, but the water collection pipe hinders the flow of water,
It becomes difficult to flow between the elements. As a countermeasure against this, it is conceivable to increase the interval between the membrane elements. However, in this case, the membrane filling rate decreases and the membrane area decreases.

The present invention solves the above-mentioned conventional problems, and can increase the membrane filling rate of the hollow fiber membrane module to obtain a large membrane area, and can surely prevent blockage of the intermembrane flow path. It is an object of the present invention to provide an immersion type membrane separation apparatus which can always obtain a high flux.

[0021]

According to the immersion type membrane separation device of the present invention, a large number of hollow fiber membranes are provided in parallel , and both ends of the hollow fiber membranes are provided.
In the immersion type membrane separation apparatus in which a plurality of hollow fiber membrane elements held by a water collecting pipe are disposed in a tank, each element has a longitudinal direction of the hollow fiber membrane parallel to a flowing direction of raw water. It is installed so as, and adjacent to
The distance b in the raw water flow direction of the water collection pipe of the element
0.4 to 2 times the outer diameter a of the collecting pipe,
Of the water collection pipe in the direction perpendicular to the raw water flow direction
The position of the end of the adjacent element on the upstream side in the raw water flow direction is made different in the raw water flow direction so that c is 0 to 0.5 times the outer diameter a of the water collecting pipe .

In the present invention, the position of the end of the adjacent element on the upstream side in the raw water flow direction is made different in the raw water flow direction. Therefore, even if the distance between the adjacent elements is reduced, the distance between the water collection pipes is reduced. The flow of raw water flowing between the elements through the element is hardly attenuated. This prevents concentration and accumulation of suspended matter on the film surface. Also, by reducing the interval between the elements, the film filling rate is increased,
The film area can be increased. Note that the film filling rate is 3
Can be increased by more than a percentage.

In the present invention, since the hollow fiber membrane module is installed so that the raw water flow and the longitudinal direction of the hollow fiber membrane are parallel to each other, the conventional example shown in FIGS. ), The density of the hollow fiber membranes in the vicinity of the water collecting tube holding portion does not occur, and the packing density becomes substantially equal over the entire module. For this reason, blockage of the transmembrane flow channel due to local densification of the hollow fiber membranes is prevented.

In the present invention, since the hollow fiber membrane extends in the flow direction of the raw water, even if the tension applied to the hollow fiber membrane is small, the hollow fiber membrane is locally densely formed even at the end of the water collecting pipe. It doesn't matter. Therefore, according to the present invention, it is possible to prevent the inter-membrane channel from being blocked without applying a large tension to the hollow fiber membrane.

In particular, in the present invention, when aeration is performed at the lower part of the hollow fiber membrane module in which the longitudinal direction of the hollow fiber membrane is vertical, the circulating flow given by the aeration becomes a strong turbulent flow. In addition, the water collection pipe itself promotes turbulence, and the clogging of the transmembrane channel is more reliably prevented.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, immersion of the invention with reference to the accompanying drawings
An embodiment of the immersion type membrane separation device will be described.

FIG. 1 shows the arrangement of the external pressure type hollow fiber membrane element 2 of the immersion type membrane separation device of the present invention, wherein (a)
The figure is a plan view, the figure (b) is a front view, the figure (c) is a side view along the line CC of the figure (b), and the figure (d) is an explanatory view of the raw water flow in the figure (c).

A large number of hollow fiber membranes 1 are arranged side by side in the form of a screen, and a plurality of screen-shaped external pressure type hollow fiber membrane elements 2 in which both ends of each hollow fiber membrane 1 are held by water collecting pipes 3, 3.
The adjacent elements 2 and 2 are arranged at intervals so that the screen surfaces of the elements 2 are parallel to each other and the longitudinal direction of the hollow fiber membrane is parallel to the raw water flow.

The water collecting pipes 3 of the adjacent elements 2 have different positions in the raw water flow direction (upward flow in this embodiment). In this embodiment, the lower collecting pipe 3 of the odd-numbered element from the left side in FIG. 1C is located lower than the lower collecting pipe 3 of the even-numbered element.
The lower collecting pipes 3 of the odd-numbered elements 2 are located at the same height, and the lower collecting pipes 3 of the even-numbered elements 2 are also located at the same height.

The upper collecting pipe 3 of each element 2 has the same arrangement as the lower collecting pipe 3 as shown.

When the element 2 is used by being immersed in a raw water tank, one of the water collecting pipes 3 of the element 2 is located below and the other water collecting pipe 3 is located above, and the screen surface and the hollow fiber membrane are arranged. It is preferable to install the device so that the extending direction of the device 1 is vertical.

[0032]

In the present invention, the distance b in the raw water flow direction between the adjacent water collecting pipes 3 is set to 0.4 to 2 times the outer diameter a of the water collecting pipes 3, and the distance b of the water collecting pipes 3 of the adjacent elements 2 is adjusted .
The interval c in the direction orthogonal to the raw water flow direction is 0 to 0.
5 times, preferably it shall be the order of 0.1 to 0.2 times.

The outer diameter a of the collecting pipe is usually about 30 to 70 mm.

Regarding the holding state of the hollow fiber membrane, as described above, if the hollow fiber membrane is held with excessive tension, the hollow fiber membrane may be damaged. Is the maximum interval, that is, 94 to 98 of the interval K _max when the hollow fiber membrane is held in the most tensioned state.
% Is preferable.

By arranging the elements 2 in such a manner that the water collecting pipes 3 of the adjacent elements are alternately arranged, the interval between the elements 2 can be reduced, the film filling rate is increased, and the membrane area is increased. Can be larger. Further, the flow velocity of the water flowing between the elements 2 can be increased to prevent the suspended substance from adhering to the membrane surface.

That is, when the heights of the water collecting pipes 3 of the element 2 are all uniform as in the comparative example of FIG.
The distance between the lower collecting pipes 3 is reduced, and the upward water flow is obstructed by the collecting pipes 3. In order to prevent this, the interval between the lower collecting pipes 3 must be increased. However, in this case, the film filling rate decreases, and the film area decreases. In addition, in the comparative example of FIG. 8A, as a result of the upward flow being obstructed by the lower water collecting pipe 3, the water flow stagnates near the upper surface of the lower water collecting pipe 3, as shown in FIG. 8B. The suspended substance concentrates and accumulates on the upper surface portion and the hollow fiber membrane in the vicinity thereof, and the membrane in that portion is closed, and the effective membrane area decreases. A decrease in the effective membrane area appears as a decrease in the amount of filtered water or an increase in the differential pressure of filtration, making the filtration process inefficient and shortening the duration of filtration. Further, the suspended substance concentrated and deposited in this manner is difficult to be peeled off even by the washing operation, which hinders the washing operation.

On the other hand, as shown in FIG.
By disposing, the distance between the elements 2 can be reduced and the distance between the adjacent water collecting pipes 3 can be increased, so that the membrane filling rate is improved and the raw water flows between the elements 2 at a high flow rate. Can be. In addition, since the water flow is sewn between the collecting pipes as shown in FIG. 1D, no suspended matter is deposited on the film surface above the collecting pipe 3.

Further, such a flow as to sew between the collecting pipes promotes the turbulence of the water flow to promote the agitation of the membrane surface. Concentration and accumulation of suspended solids can be effectively prevented, and the filtration efficiency increases.

[0040]

The present invention will be described below in detail with reference to examples and comparative examples.

Example 1 has the configuration shown in FIGS. 1A to 1C, where a = 50 mm, b = 30 mm, and c = 5 mm.

Comparative Example 1 has the configuration shown in FIG.
0 mm and c = 5 mm.

In each of Example 1 and Comparative Example 1, the membrane element was immersed in activated sludge of MLSS10000 mg / l, and filtered at a membrane permeation flux of 0.3 m ³ / m ² / day. The membrane used was a polyethylene MF membrane having a nominal pore size of 0.1 μm. Nominal membrane area of one element is 4m
² , and a module in which five of these were integrated was used for the test. At this time, 240 NL /
min (1 Nm ³ / m ² / m per cross-sectional area of an empty tower in the membrane filtration unit)
In) the air was aerated.

As a result, in both cases, the initial differential pressure was about 5 kPa
However, the element shown in FIG.
The differential pressure increased to Pa or more, and the filtration became practically impossible.
At this time, a large amount of dewatered cake-like sludge was attached to the membrane surface. On the other hand, it was found that the element of FIG. 1 according to the present invention had a differential pressure of 25 kPa or less even after the lapse of one month, and was able to operate sufficiently stably. Observation of this element one month later showed that almost no sludge adhered to the membrane surface, indicating that the membrane surface was sufficiently stirred.

[0045]

As described above in detail, according to the immersion type membrane separation device of the present invention, a plurality of screen-like external pressure type hollow fiber membrane elements are arranged such that the screen surface of each element is parallel to the flow direction of raw water. And the position of the end of the adjacent element on the upstream side in the raw water flow direction is made different in the raw water flow direction, thereby increasing the risk of breakage of the hollow fiber membranes, without blocking the flow path between the membranes. And a high flux can be obtained over a long period of time.

The immersion type membrane separation device of the present invention has the following features.
In particular, it is extremely effective in improving and stabilizing the membrane filtration efficiency of the suspension solution.

[Brief description of the drawings]

FIG. 1 shows the arrangement of hollow fiber membrane elements in a membrane separation device of the present invention, wherein FIG. 1 (a) is a plan view and FIG.
The figure is a front view and the figure (c) is a side view. (D) is a schematic diagram showing the flow of raw water.

FIG. 2 (a) is a front view showing a screen-shaped external pressure type hollow fiber membrane element, and FIG. 2 (b) is a plan view thereof.

FIG. 3 is a front view showing a conventional module installation method.

FIG. 4 is a schematic diagram showing a state of a hollow fiber membrane element in a raw water flow.

FIG. 5 is an enlarged view of a portion Z in FIG. 4;

FIG. 6 is a diagram showing the relationship between the distance between the water collecting pipe holding parts at both ends of the hollow fiber membrane and the angle of the hollow fiber membrane near the water collecting pipe holding part with respect to the horizontal line.

FIG. 7 is a diagram showing the relationship between the distance between the water collecting tube holding portions at both ends of the hollow fiber membrane and the tension of the hollow fiber membrane.

FIG. 8A is a front view showing an element arrangement according to a comparative example. (B) is a schematic diagram showing the state of adhesion of the suspended substance.

[Explanation of symbols]

1 hollow fiber membrane 2 Screen type external pressure type hollow fiber membrane element 3 Water collection pipe S screen surface

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 63/02 C02F 1/44

Claims (2)

(57) [Claims] 1. A large number of hollow fiber membranes is arranged, the hollow fiber
In a submerged membrane separation device having a plurality of hollow fiber membrane elements in which both ends of a membrane are held by a water collecting pipe are arranged in a tank, the longitudinal direction of each element is parallel to the flow direction of raw water. In the direction of raw water flow of the water collection pipe of the adjacent element.
The distance b is 0.4 to 2 times the outer diameter a of the collecting pipe, and
Element in the direction perpendicular to the raw water flow direction
Interval c is 0 to 0.5 times the outer diameter a of the collecting pipe.
, The immersion is characterized in that at different positions of the end portion of the raw water flow direction upstream side of the adjacent elements to raw water flow direction
Pickled membrane separation device. 2. The method according to claim 1, wherein both ends of said hollow fiber membrane are maintained.
The distance K between the holding parts keeps the hollow fiber membrane in the most tensioned state
Is between 94% and 98% of the interval K _max
Immersion type membrane separation equipment.