JPH08257378A - Membrane separator - Google Patents

Abstract

PURPOSE: To provide a sufficiently small-sized membrane separator bringing jet air into contact with membrane surfaces of membrane elements in a uniformly dispersed state to efficiently wash membranes in a membrane separator wherein flat membrane elements are arranged in the liquid to be treated in a treatment tank so that the membrane surfaces of them become vertical and an air diffusion means is provided under the membrane elements to bring air- liquid mixed streams into contact with the membrane surfaces to raise them. CONSTITUTION: An enclosure wall 32 is provided in contact with the bottom surface 11 of a treatment tank at the lower end thereof under membrane elements 2 and air diffusing means 4 are provided within the enclosure wall 32 so that the air diffusion orifices thereof are turned downwardly and the height of the enclosure wall 32 is set so that the air-liquid mixed streams at the lower end position of the membrane elements are made almost parallel.

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, and is particularly useful for purifying domestic wastewater and industrial wastewater.

[0002]

2. Description of the Related Art When a suspension is subjected to purification treatment by a membrane separation method, a plurality of flat membrane elements having semipermeable membranes provided on both sides of a filtrate flow channel member are arranged side by side in a stock solution tank. An air diffuser is installed below the element group, the suspension is supplied into the stock solution tank, and air is scrubbed by the air blown from the air diffuser while the pressure is reduced on the filtrate flow channel side of the membrane element to suspend it. It is known to filter a liquid (Japanese Patent Publication No. 4-70958).
Issue).

In this membrane separation, particularly when the suspension contains a large amount of organic matter such as domestic wastewater and factory wastewater, the organic matter in the wastewater is adsorbed and metabolized under aerobic conditions by the activated sludge in a floating state. Pathogenic bacteria are reduced by decomposition and activated sludge grows. That is, the microbial reaction also progresses.

In this case, in order to prevent the formation of the cake layer on the membrane surface and to suppress the decrease in the filtration flow rate, the air blown out from the air diffusing tube is used to prevent the formation of a cake layer on the membrane surface despite the suspension of the activated sludge in high concentration. It is necessary to disperse it evenly over the surface. Therefore, conventionally, a long casing having a length of 500 mm to 2000 mm is provided below the membrane element, and an air diffuser is provided at the lower end of the casing, and gas-liquid mixing is performed by the air blown from the air diffuser. It has been proposed that the flow be made into a parallel flow until it reaches the upper end position of the casing, and the air is brought into uniform contact with the membrane surface of the membrane element (Japanese Patent Laid-Open No. 5-277).
345).

[0005]

However, in such a structure, it is necessary to provide a long casing portion below the membrane element, which inevitably increases the height of the device.

An object of the present invention is to dispose a flat membrane element in a liquid to be treated in a treatment tank with its membrane surface being vertical.
In a membrane separation device in which an air diffuser is provided below the membrane element and the gas-liquid mixed flow rises in contact with the membrane surface by the air diffuser, jet air is brought into uniform contact with the membrane surface to form a membrane. An object of the present invention is to provide a sufficiently small membrane separation device that can efficiently perform cleaning.

[0007]

Means for Solving the Problems In a membrane separation apparatus according to the present invention, a flat membrane element is disposed in a liquid to be treated in a treatment tank with its membrane surface vertical, and is placed below the membrane element. In a device provided with an air diffuser, and the gas-liquid mixed flow is raised by contacting the membrane surface by the air diffuser, an enclosure wall is provided below the membrane element, and the air diffuser is provided in the enclosure wall. The means is provided with the air diffuser facing downward, and the height of the surrounding wall is a length that makes the gas-liquid mixed flow at the lower end position of the membrane element substantially parallel, Normally, the rising velocity of gas-liquid mixing is 0.01-2m / sec.
The height of the surrounding wall is 200 mm to 500 mm.

The structure of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing a membrane separation device according to the present invention. In FIG. 1, 1 is a processing tank. Reference numeral 2 denotes a flat membrane element, and a plurality of membrane elements are arranged side by side in the frame 31 so that the membrane surface 21 is vertical. 32 is the membrane element 2,
It is an enclosure wall provided below, and its lower end is in contact with the bottom surface 11 of the processing tank. 4 are air diffusers provided in the surrounding wall 32, and the air diffuser 41 is directed downward. The downward direction (air ejection angle) of the air diffuser 41 may be within a range of ± 45 ° with respect to the direct downward direction.

The gas-liquid mixed flow due to the air blown out from the diffusing port 41 of the air diffusing pipe 4 becomes a non-uniform flow at the bottom of the surrounding wall, but the reflected flow from the bottom surface 11 of the processing tank becomes a parallel flow as it goes upward. As a result, the length of the surrounding wall 32 is set so that the gas-liquid mixed flow at the upper end 321 of the surrounding wall becomes a parallel flow. In this case, the height of the surrounding wall 4 at which the gas-liquid mixed flow at the upper end 42 of the surrounding wall can be a parallel flow becomes longer as the flow velocity of the gas-liquid mixed flow becomes higher. Therefore, since the flow velocity of the gas-liquid mixed flow is usually 0.01 to 2 m / sec, the height of the surrounding wall 4 is usually 200 mm or more, and 500 mm.
Since the length is too long and the height of the device is increased, the length is set to 500 mm or less.

In order to treat a suspension such as sewage such as domestic wastewater and factory effluent by the membrane separation apparatus according to the present invention, in FIG.
Is supplied to the upper end 32 of the enclosure wall 32 by driving the blower 51 to eject air from the diffuser tubes 4 ,.
The gas-liquid mixed flow is made into a parallel flow before reaching 1, and this parallel flow is raised along the gap between the flat membrane elements 2 and 2,
The membrane surface 21 is air-scrubbed by this gas-liquid mixed upflow, while the membrane element 2 is driven by the suction pump 53.
The pressure on the filtrate flow path side of is reduced to generate a predetermined transmembrane pressure difference,
Under contact with air, organic matter in sewage is adsorbed and metabolized by aerobic microorganisms to reduce pathogenic bacteria and to grow aerobic microorganisms, while allowing water to permeate the membrane of membrane element 2 and removing the filtrate. Filtrate storage tank 5 via pipe 54
Take out to 5.

The rising speed of the gas-liquid mixed flow varies depending on the quality and concentration of the suspension, the processing speed, etc., but is usually 0.0
1-2 m / sec, preferably 0.02-1 m / se
c. If it is 0.01 m / sec or less, activated sludge will be difficult to precipitate to promote microbial reaction, and the cleaning effect on the membrane surface will be insufficient. If it is 2 m / sec or more, it is difficult to ensure security and the air supply cost is too high due to the strength of the module. The jetting linear velocity of air from the diffuser for obtaining such a gas-liquid mixing flow velocity is 10 to 20 m / sec.
That is all. In this case, the height of the surrounding wall is 200 mm to 500 mm as described above. The position of the air diffusing tube in the enclosure wall is not likely to be a parallel flow at the air diffusing port due to the opposing jets (jet from the air diffusing port and reflection jet from the bottom of the processing tank), so at least 200 mm from the lower end of the membrane element. It is preferable that the positions are separated from each other.

The dimensions of the membrane element are usually 50 cm to 150 cm in height, 20 cm to 100 cm in width, and 3 mm to 6 mm in thickness. Membrane element 2, 2
The mutual interval between them varies depending on the water quality of the stock solution and the like, but is usually about 5 to 15 mm. If it is 5 mm or less, the resistance against the rise of the gas-liquid mixed flow between the membrane elements becomes too high, and the cleaning effect of the membrane surface is reduced. If it is 15 mm or more, the membrane area becomes too small with respect to the volume of the stock solution tank. Larger size is invited. In the configuration example of the membrane separation apparatus according to the present invention described above, the lower end of the enclosure wall is in contact with the bottom surface of the processing tank, but within the limit that the leakage of air between the lower end of the enclosure wall and the bottom surface of the processing tank can be kept slightly. A slight gap may be provided (for example, when the frame 31 is suspended and supported by a hook).

When the membrane separation device according to the present invention is used,
The pressure reduction by the suction pump 53 on the filtrate flow path side of the membrane element 2 is preferably performed intermittently (for example, the suction pump is driven for 10 minutes and the suction pump is stopped for 5 minutes repeatedly).
By doing so, during the suction pump stop period, the transmembrane pressure difference is set to zero, and the pressing of the cake layer onto the membrane surface is avoided, and the air pressure is reduced.
The cake layer can be efficiently removed by scrubbing,
It is possible to suppress the time-dependent adhesion and formation of the cake layer.

In this case, in order to keep the filtration flux constant despite the formation of the cake layer on the membrane surface over time, the cake is kept.
In accordance with the increase in filtration resistance due to the formation of the bed layer, the pressure reduction degree (the pressure reduction degree during the pressure reduction in the intermittent pressure reduction operation) is gradually increased to increase the transmembrane pressure difference, and the predetermined pressure reduction degree (for example, −50 KPa). When it reaches a certain level, the operation can be stopped, the filtration flux can be almost recovered by an appropriate means, and then the re-operation under the constant filtration flux can be performed (quantitative operation). Alternatively, the pressure is intermittently reduced at a constant decompression degree, and when the permeation flux falls to the lower limit value, the operation is stopped, the filtration flux is almost recovered by an appropriate means, and then the above-mentioned constant decompression degree is maintained. It can also be restarted (constant pressure operation).

In the present invention, as the flat membrane element, for example, a membrane element having a structure shown in (a) of FIG. 2 and (b) of FIG. 2 [a cross-sectional view taken along line (a) of (a) of FIG. 2] is used. can do. In FIG. 2A and FIG. 2B, 22 is a sheet for filtered liquid flow path, for example, a plastic net, a plastic non-woven fabric, a woven fabric (for example, a polyester tricot woven fabric, particularly this woven fabric). A resin liquid such as a melamine resin liquid solidified so as to leave a fiber gap inside) or a porous plastic plate is used. Reference numeral 23 denotes a filtrate (collection of vinyl chloride resin) or lightweight metal (eg, of aluminum) filtrate liquid collecting pipe member (outer shape is quadrangular), and 24 is a reinforcing edge plate of the filtrate liquid collecting pipe member 23. One end of the filtered liquid flow path sheet 22 is inserted into the beak portion 231, and the reinforcing edge plate 24 is attached to the three sides of the filtered liquid flow path sheet 22 by tightening the bolts 241 to bond the chiral surfaces. It is sealed with the agent 251. 21 is a beak portion 231 of the filtered liquid collecting pipe member 23.
Is a semipermeable membrane (microfiltration membrane, ultrafiltration membrane, etc.) adhered by adhesive 252 or fusion bonding over the reinforcing edge plate 24, and the microfiltration membrane or ultrafiltration membrane is attached to a substrate such as a nonwoven fabric. A combined product, a microfiltration membrane or an ultrafiltration membrane in which a base material such as a non-woven fabric is embedded can be used. Reference numeral 26 is a short pipe for taking out the filtrate, which is watertightly inserted into the upper end opening of the filtrate collecting pipe member 23 with an adhesive, and 27 is also the filtrate collecting pipe portion 23.
It is a watertight plug that is watertightly inserted into the lower end opening of the via an adhesive.

[0016] In the above, the seals of the mating surfaces of the reinforcing edge plates 24, 24, the attachment of the semipermeable membrane 21, the short pipe 26 for removing the filtrate.
As the adhesive used for fixing the sealing plug 27 in a watertight manner, for example, a curable adhesive such as an epoxy resin or a urethane resin, a hot melt adhesive, or the like can be used.

In the main body of the membrane separation apparatus according to the present invention, for example, as shown in FIG. 3, a plurality of frame portions 31 of the stationary frame 3 having a surrounding wall 32 at the lower end of the frame portion 31 are provided. It can be assembled by inserting the membrane elements 2, ... with a gap between the membrane elements, and disposing the air diffuser tubes 4, ... in the surrounding wall 32 with the air diffuser port facing downward. The air diffuser may be arranged either in the same direction as the membrane element 2 or in the orthogonal direction as shown in FIG. 4 (a) or FIG. 4 (b), and as shown in FIG. 4 (c). A loop-shaped diffuser tube can be arranged.

[0018]

The diffusing pipe 4 is arranged in the surrounding wall 32 below the membrane element 2 with the diffusing port 41 facing downward, and the gas-liquid mixed flow due to the air blown from the diffusing port is at the bottom of the surrounding wall. Although it becomes a non-uniform flow, the reflected flow from the bottom surface 11 of the processing tank becomes a parallel flow as it goes upward, and the upper end 3 of the surrounding wall
At 21, a parallel flow is formed, and the gas-liquid mixed flow comes into contact with the membrane surface 21 of the membrane element 2 by this parallel flow, so that the membrane can be uniformly washed by the uniform dispersion of air on the membrane surface, and the cake layer Generation can be well prevented, and the initial filtration flow rate can be sufficiently maintained. In this case, the gas-liquid mixed flow at the upper end of the enclosure wall can be made into a parallel flow with a lower enclosure wall height, and the height of the upper end position of the membrane element can be reduced to make the device smaller than in the case where the air diffuser is directed upward. it can.

[0019]

【Example】

[Example] The membrane element includes (a) and (b) in FIG.
Use the one shown in, and the dimensions are 1060 mm length x width (width)
610 mm, the membrane 21 is a polyolefin microfiltration membrane having a nominal pore diameter of 0.4 μm and an area of 1 m ² , and the sheet 22 for the filtrate flow path is a plastic net.
Urethane resin was used for both the adhesion between the frame plate and the film and the adhesive seal between the frame plates. The apparatus main body has the configuration shown in FIG. 3, the height of the surrounding wall 32 is 480 mm, and the above-mentioned 30 membrane elements are 13 mm in the frame portion 31 of the stationary frame 3.
Were overlapped and inserted at intervals of, and the air diffusing tube 4 was arranged at a position 450 mm below the membrane element 2 with the air diffusing port facing downward.

This apparatus main body is installed in a treatment tank, an activated sludge solution having an MLSS concentration of 6,000 to 7,000 mg / liter is used as a liquid to be treated, and a gas-liquid mixed flow on the membrane surface of the membrane element is used. The air jet rate was set so that the flow velocity was 0.5 m / sec, and the suction pump was operated for 10 minutes to keep the filtration flux at 0.6 m ³ / m ² · day. It was operated under reduced pressure.

[Comparative Example 1] The same as Example 1 except that the air diffuser of the air diffuser was directed right above. [Comparative Example 2] The height of the surrounding wall is 180 mm as compared with the embodiment.
The same as in the example, except that the air diffuser was arranged at a position 150 mm below the membrane element with the air diffuser facing downward. In this comparative example, the lower end portion of the membrane element was exposed to the jet area due to the collision on the bottom surface of the processing tank.

In the above Examples and Comparative Examples, after the start of the filtration process, the filtration pressure on the filtrate flow path side of the membrane element under the filtration flux of 0.6 m ³ / m ² · day was maintained (the suction pressure during the intermittent operation of the suction pump). The pump operating pressure) is as shown in FIG. 5, and in the example, the increase in filtration resistance over time is small as compared with the comparative example, and the degree of pressure reduction can be made small.
Therefore, it is clear that the cake layer is less generated.

[0023]

According to the present invention, a flat membrane element is disposed in a liquid to be treated in a treatment tank with its membrane surface vertical, and an air diffuser is provided below the membrane element. In the membrane separation device in which the gas-liquid mixed flow is raised by contacting the membrane surface by the air diffusing means, even if the height of the surrounding wall for housing the air diffusing means below the membrane element is lowered, the case on the membrane surface is reduced. -It is possible to provide a membrane separation device which can well suppress the formation of a bed layer, has a compact height, and has a stable filtration flow rate.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing an example of a membrane element used in the present invention.

FIG. 3 is an explanatory diagram showing an example of a membrane separation device body used in the present invention.

FIG. 4 is an explanatory diagram showing a different arrangement example of the air diffusing tubes used in the present invention.

FIG. 5 is a diagram showing a depressurized state of the membrane element on the filtrate flow path side under quantitative filtration of an example according to the present invention and a comparative example.

[Explanation of symbols]

 1 Processing Tank 2 Flat Membrane Element 21 Semipermeable Membrane 32 Enclosing Wall 4 Diffuser Tube 41 Diffuser Port 53 Suction Pump 54 Filtrate Extraction Pipe

Claims (2)

[Claims] 1. A flat membrane element is disposed in a liquid to be treated in a treatment tank with its membrane surface vertical, and an air diffuser is provided below the membrane element. In a device in which a liquid mixed flow is raised in contact with the membrane surface, an enclosing wall is provided below the membrane element, and the air diffusing means is provided in the enclosing wall with the air diffusing port facing downward. A membrane separation device, wherein the height of the surrounding wall is such that the gas-liquid mixed flow at the lower end position of the membrane element is substantially parallel. 2. The rising velocity of the gas-liquid mixed flow is 0.01 to 2 m /
The membrane separation device according to claim 1, wherein the height is sec and the height of the surrounding wall is 200 mm to 500 mm.