JPH10128085A - Operating method of membrane separation device - Google Patents

Abstract

(57) [Summary] Filtration of a membrane element 2 while immersing a membrane element 2 having a filtrate side inside in a stock solution, swirling the stock solution by a diffuser 3, and washing the membrane surface with the stock solution flow. In a membrane separation method in which the undiluted solution is filtered by depressurizing the liquid side, particularly in a membrane separation activated sludge treatment method, it is possible to obtain a constant filtration flux at a stable degree of reduced pressure, that is, to enable long-term stable operation. An undiluted liquid flow abnormality detector is provided in the undiluted liquid,
By detecting an abnormality of the undiluted swirl flow, the swirl flow is restored to a normal state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a membrane separation apparatus used for treating sewage such as human waste, sewage, domestic wastewater, and industrial wastewater.

[0002]

2. Description of the Related Art Recently, a gravity separation activated sludge treatment method, which is a traditional treatment method for human waste, sewage, domestic wastewater, and industrial wastewater (hereinafter referred to as sewage) (microbial decomposition treatment in an aeration tank,
A membrane separation activated sludge treatment method is attracting attention as an alternative to the method of introducing the treated wastewater into a sedimentation separation chamber, separating the activated sludge by gravity separation, and returning a part of the separated sludge to an aeration tank. .

In this treatment method, solid-liquid separation is carried out by filtration using a membrane module, a filtrate is taken out, and excess sludge is directly drawn out from an aeration tank, and MLSS (mixed liquid floating solids) in the aeration tank is used. The MLSS in the aeration tank can be significantly reduced compared to the gravity separation method, and the size of the entire apparatus can be reduced because the sedimentation separation chamber is unnecessary. Since the concentration can be maintained at a high level, there are advantages that, unlike the gravity separation method, dehydration during the treatment of excess sludge is reduced, and energy consumption of operating energy can be reduced.

[0004] In the present applicant, a sewage treatment apparatus using a membrane separation method is described as "a membrane module having an air diffuser and having a vertical passage along the membrane surface is disposed immediately above the air diffuser. And a diffuser-type aeration tank provided with means for reducing the pressure on the membrane filtration side of the membrane device ”(Japanese Patent Publication No. 4-70).
958, Patent No. 1874881). As the membrane module of this apparatus, it is preferable to stack flat membrane elements so as to maintain a vertical passage therebetween.

To treat sewage using this aeration type aeration tank, the undiluted solution in the tank is swirled by air bubbling of air spouted from the aeration device, and organic matter in the sewage is brought into contact with air.
Adsorbed and metabolized and decomposed by aerobic microorganisms to reduce organic matter and grow aerobic microorganisms, and to control the production of sludge gel layer on the membrane surface by the undiluted solution flow along the membrane surface of the membrane element, and the filtrate of the membrane element The pressure on the side is reduced to generate a transmembrane pressure, and water is separated from the activated sludge by filtration under the transmembrane pressure.

[0006]

In this membrane separation, suspended sludge in the undiluted solution adheres to the membrane surface over time and the filtration resistance increases. Therefore, it is necessary to maintain the filtration flux I constant. , The pressure of the membrane element on the filtrate side, ie, the transmembrane pressure difference, must be gradually increased. Thus,
According to the inventor's experience, it is necessary to increase the pressure reduction degree ΔP at a certain point in time.

The inventors of the present invention have investigated the cause and found that the gap between the membrane elements (the membrane area ratio with respect to the volume of the stock solution treatment tank was increased due to insufficient air volume and unevenness of the air diffuser). To reduce the size of the separation device,
Activated sludge adheres and accumulates in the middle of a stock solution swirling flow path such as a frame of a membrane module or the like, and this becomes an obstacle to the stock solution swirling flow, and the stock solution swirling flow is weakened, and the membrane surface is reduced. It was found that one of the main causes was that the sludge gel layer formation suppression effect due to the undiluted solution flow was reduced and the sludge gel layer formation increased at an accelerated rate.

An object of the present invention is to immerse a membrane element having a filtrate side on the inner side in a stock solution, swirl the stock solution by aeration means, and wash the membrane surface with the stock solution flow while cleaning the membrane surface with the stock solution flow. In a membrane separation method in which a stock solution is filtered under reduced pressure, particularly in a membrane separation activated sludge treatment method, it is an object to obtain a constant filtration flux at a stable pressure reduction degree, that is, to enable a long-term stable operation.

[0009]

According to a method of operating a membrane separation apparatus according to the present invention, a membrane element having an inner side as a filtrate is immersed in a stock solution, the stock solution is swirled by aeration means, and the membrane surface is unprocessed. In an operation method of a membrane separation device for filtering a stock solution by depressurizing a filtrate side of a membrane element while washing by flowing,
The undiluted liquid flow abnormality detector is disposed in the undiluted solution, and the undiluted liquid swirl flow is detected to be abnormal to recover the swirl flow to a normal state. -Can be used, and the abnormality of the undiluted liquid swirl flow can be detected by issuing an alarm.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing a membrane separation device used in the present invention. In FIG. 1, reference numeral 1 denotes a stock solution treatment tank, which can use an aeration tank body of a conventional aeration-type aeration tank using an activated sludge method. Are membrane elements disposed at predetermined intervals in the undiluted solution treatment tank, and have a filtrate flow path therein. Reference numeral 20 denotes a filtrate collection pipe of the membrane element 2, which is connected to a filtrate flow path in the element, and the filtrate that has passed through the membrane is collected in the filtrate collection pipe via the filtrate flow path. Are diffusion tubes provided below the membrane elements 2,.
The undiluted solution is disposed in the gap between the two so that it can be efficiently raised by air bubbling. The stock solution is swirled into the stock solution processing tank 1 by this air bubbling. 31 is a diffuser 3
And 32 is a blower. 4 is a filtrate extraction pipe connected to the filtrate collecting pipes 20 of the membrane elements 2,..., 41 is a decompression pump inserted into the pipe 4,
42 is a filtrate storage tank. Reference numeral 51 denotes a stock solution supply pipe, and reference numeral 52 denotes a liquid feed pump inserted into the pipe 51.

Reference numeral 6 denotes an undiluted liquid flow abnormality detector. An undiluted solution, for example, a pressure sensor for detecting the dynamic pressure of the undiluted swirl flow (for example, a strain gauge type pressure sensor) can be used. In addition, it is also possible to use a sensor for detecting an abnormal wave on the liquid surface due to an abnormal flow of the undiluted solution, for example, an abnormal frequency or wave height.

FIG. 2 (a) and FIG. 2 (b) [a cross-sectional view taken along a roll in FIG. 2 (a)]
And a filtrate flow path material 22 (for example, woven cloth, non-woven cloth, net, etc.) in a frame 20 having a filtrate collection pipe 21.
And a flat membrane 23 (microfiltration membrane, ultrafiltration membrane, etc.) is adhered to both sides of the frame with an adhesive 24. The flat membrane 23 is formed by laminating a membrane on a supporting substrate, Embedded with a woven fabric, a non-woven fabric or the like can be used. 3 (a) and 3 (b) [a cross-sectional view taken along a line in FIG. 3 (a)]
Another example of the above membrane element is shown. Filtrate passage grooves 201,... Are formed on both sides of the plate 20, and a filtrate outlet hole communicating with the filtrate passage grooves 201,. 202, a filtrate passage spacer 21 and a flat membrane 23 are sequentially laminated on each side of the plate 20, and the periphery of the flat membrane 23 is sealed on each side of the plate with an adhesive. is there. The dimensions of the membrane element 2 are generally 50 cm to 150 cm in height and 20 cm to 100 c in width when the dimensions of the treatment tank are made substantially equal to the dimensions of the aeration chamber of the conventional aeration type aeration tank.
m and a thickness of 3 mm to 15 mm.

As shown in FIG. 4, the module structure of the membrane elements 2,...
Can be alternately arranged side by side through a gap for a stock solution passage, and a group in which the side-by-side group is accommodated in a frame 200 can be used. The module is placed directly on the bottom surface of the stock solution treatment tank, mounted on a gantry installed on the bottom surface, or immersed in the stock solution treatment tank in a suspended manner.

In order to operate the above-mentioned membrane separation apparatus according to the present invention, sewage (human waste, sewage, domestic wastewater, factory wastewater, etc.) is temporarily stored in a storage tank, and the wastewater is fed by a liquid feed pump 52 in FIG. The solution is supplied to the stock solution treatment tank 1, and the blower 32 is driven to blow air from the air diffuser 3 to turn the stock solution. The membrane pressure of the membrane elements 2, ... is absorbed and metabolically decomposed by the aerobic microorganisms while the organic matter in the sewage is in contact with the jet air, and the aerobic microorganisms are propagated. This is taken out to the filtrate storage tank 42 through the filtrate take-out pipe 4.

In this case, the swirling flow rate (average flow rate) of the stock solution by air bubbling at normal time varies depending on the liquid quality, concentration, processing speed, etc. of the stock solution, but is usually 0.1 to 1.0 m.
/ Sec.

The mutual spacing between the membrane elements 2, 2 is
Usually 3 to 15 mm, although it depends on the quality of the stock solution.
Degree.

In the above description, the swirling of the stock solution occurs when the stock solution is raised in the gap between the membrane elements by the air from the air diffuser, and after the rising, the stock solution is drawn from around the module or from below. However, the activated sludge concentration of the sewage is considerably high, and the space between the membrane elements and the
Activated sludge adheres and accumulates on the frame of the raw material, which becomes an obstacle to the swirling of the stock solution, and the swirling velocity of the stock solution decreases or the swirling flow distribution fluctuates. The flow of undiluted solution on the membrane surface decreases, the sludge adheres to the membrane surface rapidly, the filtration resistance increases, and a sudden decrease in filtration flux due to a sudden increase in load or a sudden increase in the degree of pressure reduction on the filtrate side of the membrane element can be avoided. Absent.

According to the present invention, the undiluted liquid swirl flow is detected by the undiluted liquid flow abnormality detector disposed at a fixed position in the processing tank, and the undiluted liquid flow is restored to normal. For example, the undiluted liquid swirling flow rate is equal to or less than the normal value (usually,
(0.1 m / sec or less), the rotation speed of the blower 32 is immediately increased, and the stock solution swirling flow rate is restored to the normal value. Therefore, it is possible to proceed with the filtration process while sufficiently maintaining the flow of the undiluted solution on the membrane surface and suppressing the adhesion of sludge to the membrane surface, preventing a sudden increase in load due to an increase in filtration resistance, and preventing the filtration flux and the membrane element from flowing. It can be operated stably without radical fluctuation of the pressure reduction degree on the filtrate side.

In the method for operating the membrane separation apparatus according to the present invention, the undiluted liquid flow abnormality detectors are provided at a plurality of positions in the undiluted liquid processing tank, and an abnormality of the undiluted liquid swirl flow is determined by comparing the plurality of detected values. Can also be detected. As the undiluted liquid flow abnormality detector, one that detects an abnormality of the flow velocity or the dynamic pressure, and one that detects an abnormality of the wave of the liquid surface, for example, an abnormality of the frequency can be used. At the same time as the abnormality detection, a normal recovery process, for example, a recovery of the normal swirling flow speed by increasing the speed of the blower can be automatically performed. In addition, the detected value can be analyzed by a computer, and when an abnormality is determined, an alarm can be issued simultaneously with the detection.

[0020]

【Example】

[Example] The membrane element shown in FIG. 2 was used,
The dimensions of the frame 20 are 1060 mm long and 610 m wide (width).
m, the maximum thickness was 13 mm, and the minimum was 2 mm. A polyolefin microfiltration membrane having a membrane area of 0.45 m ² was used on both sides of the membrane 23. The module shown in FIG. 4 was used, the number of the membrane elements 2 was 10, and the minimum distance between the membrane elements was 4 mm. Fig. 1
The ones shown in Table 1 were used. MLSS concentration of 10,000 in stock solution
Using an activated sludge solution of 0 to 15,000 mg / liter, a strain gauge type pressure gauge is provided at a predetermined position, and a diffused air flow rate is set so that the sewage swirl flow velocity at that position is approximately 0.5 m / sec. And set the decompression pump to run for 8 minutes.
Intermittent operation with a repetition of 2 minutes of stoppage and a filtration flux of approximately 0.5
The degree of pressure reduction was adjusted to m ³ / m ² · day. Five months after the start of operation, the sewage swirl flow velocity was reduced to 0.1 m / sec.
/ Sec. The degree of decompression until 8 months from the start of operation is 0.1 to 0.2 kg / cm ² ,
It was stable.

[Comparative Example] The same operation as in the example was performed except that the recovery operation of the sewage swirl velocity was not performed. After a lapse of 8 months from the start of operation, the degree of decompression is approximately 0.6 kg / cm ²
It became impossible to continue driving.

[0022]

According to the method for operating a membrane separation apparatus according to the present invention, in the treatment of sewage, in particular, the membrane separation activated sludge method, the membrane separation apparatus can sufficiently suppress the membrane contamination and sufficiently suppress the increase in load. Stable operation is possible, and stable operation is possible for a long period of time.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a membrane separation device used in the present invention.

FIG. 2 is an explanatory diagram showing an example of a membrane element in the membrane separation device of FIG.

FIG. 3 is an explanatory view showing another example of the membrane element in the membrane separation device of FIG.

FIG. 4 is an explanatory diagram showing an example of a membrane module in the membrane separation device of FIG.

[Explanation of symbols]

 Reference Signs List 1 stock solution processing tank 2 membrane element 3 air diffuser 6 stock solution flow abnormality detector

Claims (3)

[Claims] 1. A membrane element whose inside is a filtrate side is immersed in a stock solution, the stock solution is swirled by a diffuser, and the filtrate side of the membrane element is decompressed while washing the membrane surface with the stock solution flow. A method for operating a membrane separation device for filtering a membrane, comprising: arranging an undiluted liquid flow abnormality detector in the undiluted solution, and recovering the undiluted swirl flow to a normal state by detecting the undiluted swirl flow abnormality. How to operate the device. 2. The method according to claim 1, wherein a pressure sensor is used as the undiluted liquid flow abnormality detector. 3. The method for operating a membrane separation apparatus according to claim 1, wherein an abnormality of the swirling flow of the stock solution is detected by issuing an alarm.