JP3464769B2 - 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 apparatus for purifying organic wastewater such as sewage and industrial wastewater, and more particularly to cleaning a membrane unit immersed in water to be treated in a treated water tank. The present invention relates to a membrane separation device.

[0002]

2. Description of the Related Art Membrane separation devices have been well known as devices for solid-liquid separation of organic wastewater such as sewage and industrial wastewater. The membrane separation device is a device that separates and purifies the input organic wastewater by a membrane unit that is immersed in the wastewater. As such a membrane separation device, for example, one disclosed in Japanese Patent Laid-Open No. 8-257581 is known. In this device, the membrane unit includes a casing and a plurality of flat plate-shaped membrane elements arranged inside the casing at appropriate intervals. Further, a floating material such as granular activated carbon is put into the organic wastewater, and air is supplied to the organic wastewater below the membrane element. Then, an ascending flow is formed inside the membrane unit and a descending flow is formed outside, so that the floating body circulates and flows in the organic wastewater, and at the same time, the membrane element is cleaned by the floating body at the same time as the membrane separation process. Planned.

[0003]

However, in the membrane separation device described in the above-mentioned conventional publication, the membrane of the membrane element is clogged in a relatively short period of time, and the membrane separation process cannot be continued for a long time. There were cases.

In view of the above circumstances, an object of the present invention is to provide a membrane separation device capable of sufficiently preventing the clogging of the membrane.

[0005]

DISCLOSURE OF THE INVENTION As a result of studying the above-mentioned conventional problems, the present inventors have found that
When a floating material that floats in organic wastewater is used, there may be floating bodies that remain in the upper part without rising in the floating body that has once risen.If such floating bodies increase, circulating flow in organic wastewater It was found that the amount of suspended solids decreased, the membrane element was not sufficiently washed, and as a result, the membrane was clogged in a relatively short period of time. Therefore, as a result of further intensive research, the present inventors have made it possible to sufficiently circulate and float the floating body by setting the ratio of the opening area in the plane crossing the treatment tank to the occupied area of the membrane unit within a specific range. It was found that the film surface can be sufficiently blocked.

That is, according to the present invention, a treated water tank for receiving treated water, a membrane unit immersed in the treated water in the treated water tank, a floating solid floating in the treated water in the treated water tank, and In a membrane separation device provided with an air diffuser that circulates and flows suspended solids in treated water, the opening area T (m ² ) of the treated water tank and the occupied area M (m ² ) of the membrane unit in a plane that crosses the treated water tank. And a ratio satisfying the following formula: 0.15 ≦ M / T ≦ 0.9 (1).

In this case, suspended solids circulate and flow in the water to be treated by the air diffuser. Usually, suspended solids rise in the membrane unit and descend outside the membrane unit to circulate. At this time, the circulating flow provides a sufficient descending speed to the suspended solids outside the membrane unit. Therefore, even if the membrane separation is continued, the reduction of the suspended solids that circulate and flow is prevented, and the membrane surface is sufficiently washed with the suspended solids.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the membrane separation device of the present invention will be described below.

FIG. 1 is a longitudinal sectional view schematically showing an embodiment of the membrane separation apparatus of the present invention, and FIG. 2 is a transverse sectional view of the membrane separation apparatus of FIG. As shown in FIG. 1, the membrane separation apparatus receives the treated water 2 through the treated water inflow line L1, the inflow pump 1 installed in the treated water inflow line L1, and the treated water inflow line L1. The water tank 3 is provided.
The treated water 2 is stored in the treated water tank 3 and activated sludge is put therein. The membrane unit 4 is immersed in the treated water 2 in the treated water tank 3.

As shown in FIG. 2, the membrane unit 4 comprises a plurality of flat plate-shaped membrane elements 4a arranged in parallel at appropriate intervals.
And a rectangular cylindrical case 4b surrounding these four sides. The membrane element 4a is not particularly limited as long as it can separate the water to be treated 2 into treated water and solid matter, and examples thereof include reverse osmosis membranes, nano membranes, ultrafiltration or microfiltration membranes, and hollow fiber membranes. Used. In addition, the membrane unit 4 is an element support frame (not shown) assembled so as to support the membrane element 4a by a square member or the like instead of the case 4b.
May be provided.

As shown in FIG. 1, a water collecting pipe is connected to each of the membrane elements 4a, and the water collecting pipe is connected to one discharge line L2. A suction pump 5 is attached to the discharge line L2. Further, the membrane separation device includes an air diffuser 6. The air diffuser 6 performs the air scrubbing of the membrane element 4a and the treated water 2 in the treated water tank 3.
To form a circulating flow in the tank. The air diffuser 6 is composed of, for example, an air diffuser 8 arranged below the membrane element 4a to generate bubbles 7, and a blower 9 connected to the air diffuser 8 via a line L3.

Floating solids 10 are present in the water 2 to be treated. As the floating solids 10, those that float in the water 2 to be treated, that is, those that are easily fluidized and have a specific gravity of less than 1, are used. The floating solids 10 floating in the water to be treated 2 are used because they are not retained at the bottom of the treated water tank and are easy to separate and collect, as compared with the case where floating solids that do not float are used. However, one having a specific gravity of 0.3 or more, preferably 0.5 or more is used. This is because if the specific gravity is less than 0.3, the suspended solid 10 tends to be difficult to circulate and flow. The particle size of the suspended solid 10 is not particularly limited as long as it does not cause blockage between the adjacent membrane elements 4a, but from the viewpoint of recovery and outflow prevention, it is 0.5 to 3 inclusive.
About mm is preferable. The shape of the floating solid 10 may be, for example, a bead shape, a granular shape, a columnar shape, or a hollow shape, but a bead shape is preferable from the viewpoint of reducing damage to the membrane surface. As the material of the floating solid 10, for example, plastic such as polypropylene or polyethylene is used. The amount of the suspended solid 10 added to the treated water tank 3 is, for example, about 3 to 10% by volume.

In the membrane separation device having such a structure, first, the inflow pump 1 is operated, and the treated water 2 flows into the treated water tank 3 through the treated water inflow line L1. On the other hand, the suction pump 5 is operated, the water to be treated 2 is membrane-separated by the membrane element 4a, and the treated water by membrane separation is discharged from the membrane element 4a through the water collecting pipe and the discharge line L2. On the other hand, the blower 9 is operated, air is supplied to the line L3, and bubbles 7 are generated from the air diffuser 8. Then, the bubbles 7 rise in the case 4b of the membrane unit 4 to form an upward flow of the water 2 to be treated, and form a downward flow outside the case 4b, and the floating solids 10 of the membrane unit 4 are accordingly formed. The floating solids 10 that have risen in the case 4b are raised in the case 4
It goes down outside b. In this way, the floating solid 10 circulates and flows in the water 2 to be treated. The floating solid 10 is cleaned by rubbing the membrane surface while passing between the membrane elements 4a when rising.
Prevents clogging of the membrane surface.

At this time, if the circulation velocity of the water to be treated 2 is insufficient, the specific gravity of the suspended solids 10 is smaller than 1, so that
In some cases, the floating solids 10 that have once risen may remain in the upper portion without falling. When such suspended solids 10 increase, the suspended solids 10 that circulate and flow in the water to be treated 2 decrease, the membrane element 4a is not sufficiently washed, and as a result, the membrane may be blocked in a relatively short period of time. .

Therefore, as shown in FIG. 2, in the membrane separation device, the opening area T in the horizontal plane 11 that traverses the treated water tank 3 is shown.
(M ²⁾ and the ratio of the occupied area M (m ²⁾ of the membrane unit 4 in the same plane 11 (M / T) is the following formula: is configured to satisfy the relation of M / T ≧ 0.15 (1) ing.

Here, the opening area of the treated water tank 3 refers to the area of the opening region 12 surrounded by the line of intersection between the flat surface 11 and the inner wall surface 3a of the treated water tank 3. For example, when the treated water tank 3 has a rectangular parallelepiped shape, the shape of the flat surface 11 and the opening area 12 of the treated water tank 3 is a rectangle or a square, and in that case, the lengths of two orthogonal sides are A (m) and B (, respectively). m), T =
It becomes A × B (m ² ).

On the other hand, the area occupied by the membrane unit 4 means the processing
Occupied area of the membrane unit 4 within the plane 11 that crosses the water tank 3.
13 area, that is, the surface of the area surrounded by the outer periphery of the case 4b
Say product. For example, the shape of the occupied area 13 of the membrane unit 4 is
When it becomes a rectangle or a square, the length of two sides that intersect at right angles
Letting a (m) and b (m) respectively, M = a × b
(M ²).

By doing so, the floating solids 10 do not stop on the upper part of the water 2 to be treated, but the floating solids 1 circulate and flow.
Since the decrease of 0 is sufficiently prevented, the clogging of the membrane surface is sufficiently prevented. The above ratio (M / T) is 10
From the viewpoint of effective use of the above, it is preferably 0.15 or more. Further, the above ratio (M / T) is preferably 0.9 or less from the viewpoint of smoothly circulating and flowing the suspended solid 10.

The above equation (1) is derived as follows.

That is, when the floating speed of the floating solids 10 when a circulating flow is not formed in the water 2 to be treated is about 0.09 m / sec, the floating solids 1 once raised to the upper part of the water 2 to be treated.
In order for 0 to fall outside the membrane unit 4, the circulation flow velocity of the water to be treated 2 outside the membrane unit 4 needs to be 0.09 m / sec or more. Here, the circulation flow velocity is determined by the flow rate of the air blown out from the air diffuser 6, and the flow rate of the air needs to be a sufficient flow rate for cleaning the membrane surface of the membrane element 4a. Then, the flow rate of the air passing through the membrane unit 4 is about 1.5 M (m ³ / min). The flow velocity of the treated water 2 circulated by this air is about 0.5 (m / sec)
Therefore, the circulation flow rate of the water to be treated 2 is 0.5M.

Since this circulation flow rate is the same outside the membrane unit 4, the circulation flow velocity outside the membrane unit 4 is
It is a value obtained by dividing the above circulation flow rate by the flow passage area outside the membrane unit 4. Here, the flow passage area on the outer side of the membrane unit 4 is the opening area T in the plane crossing the treated water tank 3.
(M ²⁾ and the difference between the area occupied by M membrane unit 4 (m ²⁾ (T
-M) represented by (m ^2).

Therefore, the downward circulation flow rate is 0.5 M /
In order to prevent the reduction of the suspended solid 10 which is represented by (TM) and circulates, 0.5M / (TM) ≧ 0.09
Is required. When this formula is arranged, the above (1)
The formula M / T ≧ 0.15 will be derived.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the treated water tank 3
Although only one membrane unit 4 is arranged inside, a plurality of membrane units 14 may be arranged inside the treated water tank 3 as shown in FIG. 4. In this case, the occupied area M of the membrane unit 4
(M ²⁾ is the area occupied by the membrane unit 14 in the plane 11 transverse to the process water tank 3 M 'When (m ^2), M'
It is represented by x (the number of membrane units 14).

The membrane separation device of the present invention can be applied to the treatment of organic wastewater, for example, biological treatment of industrial wastewater, biological treatment of rural settlement wastewater and small-scale sewage,
CP (community plant or housing wastewater treatment facility)
It can be applied to biological treatment, leachate treatment, etc.

Next, the contents of the present invention will be described more specifically with reference to examples.

[0026]

Example (Example 1) Synthetic sewage was put into a treated water tank of a membrane separation device, and activated sludge (MLSS 1.2% by weight) was acclimated with the synthetic sewage. Further, in the synthetic sewage of the treated water tank, a membrane unit (occupied area M = 0.01725 m ² ) consisting of five A4 size flat membrane elements was immersed and arranged. Diameter 3 mm
Then, 3% by volume of a beaded floating solid made of polypropylene was added to the volume of the treated water tank. The treated water tank used had an M / T of 0.15.

The membrane separation apparatus thus prepared was subjected to membrane separation with a permeation flux of the membrane of 1.5 m ³ / m ² / day and a flow rate of blown air of 26 l / min. Then, the membrane pressure difference [kPa] after 200 hours was plotted for this membrane separation device. The result is shown in FIG. As shown in FIG. 5, no increase in transmembrane pressure was observed, and it was found that the membrane surface was sufficiently cleaned with the suspended solids.

(Example 2) A membrane separator similar to that of Example 1 was prepared except that M / T was set to 0.3, and this membrane separator was used to perform membrane separation in the same manner as in Example 1. The transmembrane pressure was measured. The result is shown in FIG. As shown in FIG.
No increase in transmembrane pressure was observed, and it was found that the membrane surface was sufficiently cleaned with suspended solids.

(Example 3) A membrane separator similar to that of Example 1 was prepared except that M / T was set to 0.5, and this membrane separator was used to perform membrane separation in the same manner as in Example 1. The transmembrane pressure was measured. The result is shown in FIG. As shown in FIG.
No increase in transmembrane pressure was observed, and it was found that the membrane surface was sufficiently cleaned with suspended solids.

(Comparative Example 1) A membrane separator similar to that of Example 1 was prepared except that M / T was set to 0.05, and the membrane separation was performed in the same manner as in Example 1 using this membrane separator. The transmembrane pressure was measured. The result is shown in FIG. As shown in FIG. 5, it was found that the transmembrane pressure was considerably increased, and the membrane surface was not sufficiently washed with the suspended solids. In addition, suspended solids did not ride on the circulating flow, and most of them floated.

(Comparative Example 2) A membrane separator similar to that of Example 1 was prepared except that M / T was set to 0.1, and this membrane separator was used to perform membrane separation in the same manner as in Example 1. The transmembrane pressure was measured. The result is shown in FIG. As shown in FIG.
The transmembrane pressure increased considerably, and it was found that the membrane surface was not sufficiently washed with suspended solids. In addition, suspended solids did not ride on the circulating flow, and most of them floated.

[0032]

As described above, according to the membrane separation apparatus of the present invention, a sufficient descending speed is given to the suspended solids outside the membrane unit by the circulation flow, so that the circulation flow is continued even when the membrane separation is continued. As a result, the floating solids are prevented from decreasing, and the film surface is sufficiently cleaned with the floating solids. As a result, the clogging of the membrane can be sufficiently prevented.

[Brief description of drawings]

FIG. 1 is a vertical sectional view schematically showing an embodiment of a membrane separation device of the present invention.

2 is a cross-sectional view schematically showing the membrane separation device of FIG.

FIG. 3 is a cross-sectional view showing dimensions of a membrane unit and a treated water tank in the membrane separation device of FIG.

FIG. 4 is a cross-sectional view showing another embodiment of the membrane separation device of the present invention.

FIG. 5 is a graph showing the relationship between M / T and transmembrane pressure difference of the membrane separators of Examples 1 to 3 and Comparative Examples 1 and 2.

[Explanation of symbols]

2 ... Treated water, 3 ... Treated water tank, 4 ... Membrane unit, 6 ... Air diffuser, 10 ... Floating solid, 11 ... Plane.

Claims (3)

(57) [Claims] 1. A treated water tank for receiving treated water, a membrane unit immersed in the treated water in the treated water tank, a floating solid floating in the treated water in the treated water tank, and In a membrane separation device comprising an air diffuser that circulates and flows the suspended solids in the water to be treated, an opening area T (m ² ) of the treated water tank in a plane that crosses the treated water tank and an occupied area of the membrane unit. A membrane separation device characterized in that the ratio with M (m ² ) satisfies the following formula: 0.15 ≦ M / T ≦ 0.9. 2. The membrane separation apparatus according to claim 1, wherein the suspended solid has a particle diameter of 0.5 to 3 mm. 3. The membrane separation apparatus according to claim 1, wherein the specific gravity of the suspended solid is 0.3 or more and less than 1.