JPH07251043A - Filtering method and filter device - Google Patents

Abstract

PURPOSE:To efficiently peel the layer of matter to be filtered deposited on the surface of a separation membrane by supplying a predetermined amt. of air to mix the same with a raw soln. to form air bubble streams along the separation membrane. CONSTITUTION:In a filter device 3, a plurality of plate-shaped membranes 4 are vertically arranged so as to be spaced apart from each other and the suction pipe 6 connected to a pump 5 is connected to the upper end parts of the membranes 4 and a first air diffusion pipes 7 are arranged under the membranes 4 while a second air diffusion pipe 8 is provided on the lateral side of the lower ends of the membranes 4. The first air diffusion pipe 7 forms air bubble streams along the surfaces of the membranes 4 and the second air diffusion pipe 8 applies vibration and an impact to the membranes 4 to peel the layer of matter to be filtered on the surfaces of the membranes 4. In order to form the air bubble streams, the amt. V1 of air supplied to the lower parts of the separation membranes 4 is set to 0.5<=V1<=380(m<3>m<-2>h<-1>) per a unit projection area of the separation membranes 4 per a unit time. By this constitution, transmission flow velocity is ensured and operation is efficiently performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for filtering an undiluted solution containing colloidal dispersed particles such as bacterial cells, particles such as polymers such as enzymes and particles such as organic substances by ultrafiltration or microfiltration. .

[0002]

2. Description of the Related Art Separation membranes have been conventionally used for separation or concentration of solutions in the food industry, separation of factory wastewater, maintenance of bacterial cell concentration when biologically purifying wastewater from toilets, washrooms, baths and kitchens. Is used. Such a separation membrane separates the membrane permeate from the stock solution by using the transmembrane pressure difference or the transmembrane concentration difference as a driving force, but the substance to be filtered is condensed into a gel over time on the surface of the separation membrane on the stock solution side. When the layer to be filtered is deposited and becomes thicker, the permeation flux of the membrane is rapidly reduced.

A technique using a bubble flow is disclosed in Japanese Patent Laid-Open No. 56-21615 or Japanese Patent Laid-Open No. 4-131182 as a means for preventing a decrease in permeation flux.
The means for preventing reduction in permeation flux disclosed in these prior arts is one that creates a flow of a bubbly flow along the membrane surface and scrapes off the filtered material layer deposited on the membrane surface.

[0004]

In the above-mentioned prior art, the qualitative relationship between the bubbly flow and the permeation flux is shown, but the quantitative relationship between the two is not shown. That is,
If the amount of gas supplied to form the bubbly flow is small, the effect of scraping off the substance layer to be filtered deposited on the separation membrane surface will not be exhibited, and if the amount of gas supplied reaches a certain amount, it will be further gas. Even if it is supplied, the scraping effect corresponding to the supply amount cannot be obtained, which is disadvantageous in terms of cost.

[0005]

In order to solve the above-mentioned problems, in the filtration method according to the first invention of the present application, the undiluted solution and the gas are mixed along the separation membrane in order to separate the filtered substance layer deposited on the surface of the separation membrane. It is assumed that the generated bubble flow is formed continuously or intermittently, and the amount of gas (V ₁ ) supplied below the separation membrane to form this bubble flow is set per unit projected area of the separation membrane and per unit time. It was set to 0.5 ≦ V ₁ ≦ 380 (m ³ m ⁻² h ⁻¹ ).

[0006] The filtration method according to the second invention of the present application,
The separation membrane surface is formed continuously or intermittently as well as continuously or intermittently forming a bubbly flow in which the stock solution and the gas are mixed along the separation membrane in order to separate the to-be-filtered substance layer deposited on the separation membrane surface. I decided to hit it. Here, the amount of gas (V ₂ ) supplied near the surface of the separation membrane to form the bubble flow and the bubbles that hit the surface of the separation membrane is, for example, V ₂ ≤ per unit area of the separation membrane and per unit time. 2000
(M ³ m ^-2 h ^-1 ).

The filtration device according to the third invention of the present application is
The separation membrane is a flat membrane arranged vertically in the stock solution,
A diffusing member for forming a bubbly flow of a mixture of a stock solution and a gas is arranged below the flat plate film, and a bubble is applied to the flat plate film to the side of the flat plate film. An air diffuser was placed.

Further, the filtration device according to the fourth invention of the present application is
The separation membrane was a hollow fiber membrane vertically suspended in the stock solution, and the hollow fiber membrane was folded back so that both ends were upward and connected to the water collecting member, and an air diffuser member was arranged at the folded portion.

Further, the filtration device according to the fifth invention of the present application,
The separation membrane is a hollow fiber membrane that is laid horizontally in the stock solution,
Both ends of this hollow fiber membrane were connected to a water collecting member, and an air diffusing member was arranged below the hollow fiber membrane.

[0010]

[Function] By supplying a predetermined amount of gas to form a bubble flow, the layer of the substance to be filtered deposited on the surface of the separation membrane can be efficiently separated, and not only the bubble flow but also the bubbles on the surface of the separation membrane to be filtered. The peeling efficiency can be further improved by directly applying the layer. Further, when filtration is continued for a long period of time, the membrane filtration characteristics are slightly deteriorated due to the transformation of the filtration target layer on the membrane surface and the slight accumulation of the fine particle components in the liquid membrane surface. Sufficient scraping of the filtration target layer on the membrane surface can prevent the membrane permeation flux from deteriorating with time.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a vertical cross-sectional view of a septic tank incorporating a filtering device according to the third invention of the present application, and FIG. 2 is AA of FIG.
FIG. 2 is a view seen from the direction, in which the septum 2 is provided in the main body 1 of the septic tank.
2 is provided, and the filtering device 3 is disposed in the space defined by the partition walls 2 and 2.

The filtering device 3 has a plurality of flat plate-like membranes 4 arranged in the vertical direction with a space therebetween, and a pump 5 is provided at the upper end of each flat-plate-like membrane 4.
Is connected to a suction pipe 6, and a first air diffusing pipe 7 is provided below each flat plate-like membrane 4, and a second diffuser pipe 7 is provided at the lower end side of each flat plate-like membrane 4.
An air diffuser 8 is arranged.

The first air diffusing tube 7 is for forming a bubble flow along the surface of the flat plate-shaped film 4, and the distance from the lower end of the flat plate-shaped film 4 rises if the distance is out of this range. 1 cm or more 2
m or less. The second air diffuser 8 is used to apply air bubbles to the surface of the flat plate-like membrane 4 to vibrate or shock the flat plate-like membrane 4 to separate the filtration target layer on the surface of the flat plate-like membrane 4. The distance of 1 cm or less may be in contact with the surface of the flat film 4.

A filtering method using the above filtering device 3 will be described below. Since the filtration method according to the first aspect of the invention separates the layer to be filtered by only the flow of bubbles, the second diffuser tube 8 is not used.

That is, in the filtration method according to the first aspect of the invention, gas such as air is supplied from below the flat plate-shaped membrane 4 through the first air diffusing tube 7 to form bubbles along the surface of the flat plate-shaped membrane 4. Form a stream. Then, a flow is generated in the septic tank by this bubble flow, and the oxygen blown by aeration (aeration) is used to remove the ammonia nitrogen (NH ₄ ⁺ ) contained in the stock solution by the nitrifying bacteria contained in the activated sludge. nitrate nitrogen (NO ₃ ^-) and nitrite nitrogen (NO ₂ ^-) are oxidized and decomposed to and undecomposed organic substance is incorporated into the activated sludge.

On the other hand, by driving the pump 5 to generate a transmembrane pressure difference in the flat plate-shaped membrane 4, the permeated liquid from which the substances to be filtered such as activated sludge are removed from the stock solution is taken out through the suction pipe 6, and Send the permeate to the disinfection room or discharge it directly as sewage. In addition to the transmembrane pressure difference, a transmembrane concentration difference, a transmembrane potential difference, or a transmembrane temperature difference may be generated to perform filtration.

When the above filtering operation is continued, FIG.
As shown in FIG. 5, the activated sludge 10 and the like are deposited on the surface of the flat plate-shaped membrane 4 on the side of the undiluted solution to form the filtered material layer 11. If the filtered material layer 11 becomes thicker, the permeation flux will decrease and the operating efficiency will decrease. However, in the first invention, the activated sludge 10 and the like are constantly peeled off by the scraping action by the bubble flow, and therefore the thickness of the filtration target layer 11 is not increased. In other words, assuming that the permeation flux is J (m ³ · m ^-2 · d ^-1 ) and the separation speed of the activated sludge 10 etc. is V (m · d ^-1 ), an equilibrium state is reached after a certain period of time. In the equilibrium state, J (m ³ · m ^-2 · d ^-1 ) = V (m ·
d ^-1 ).

However, in order for the bubble flow to exert a sufficient scraping action, it is necessary to supply a certain amount of gas or more,
It was also found from experiments that the supply of more gas than necessary does not improve the permeation flux. Figure 4
It is a graph of the said experimental result which shows how a membrane permeation | flux flux changes with progress of filtration time with the said gas amount. The experimental condition is that the pore diameter of the flat plate-shaped film 4 is Dp = 0.1μ
m, transmembrane pressure difference ΔP = 30 kPa generated in the flat plate-shaped film 4,
The temperature T of the stock solution was 20 ° C. This graph is shown on a semilogarithmic graph paper, and the filtration time on the horizontal axis is on a logarithmic scale. From this graph, it can be seen that the membrane permeation flux has a linear relationship with the logarithm of the filtration time with the gas amount (V ₁ ) as a parameter. Assuming that the membrane permeation flux when the filtration time is 5 (h) is the initial value, the gas amount (V ₁ ) is 210 (m ³ ) in the initial value.
m ^-2 h ^-1 ), 290 (m ³ m ^-2 h ^-1 ), 380 (m ³ m ^-2 h ^-1 ),
0.40 as it increases to 450 (m ³ m ^-2 h ^-1 ).
(M ³ m ^-2 h ^-1 ), 0.48 (m ³ m ^-2 h ^-1 ), 0.51 (m ³ m
^-2 h ^-1 ) and 0.52 (m ³ m ^-2 h ^-1 ). Also,
The slope of the straight line gradually becomes horizontal from the lower right. However, even when the gas amount (V ₁ ) exceeds 380 (m ³ m ^-2 h ^-1 ), the membrane permeation flux hardly increases. It can be seen that supplying a larger amount of gas than necessary does not lead to improvement of the permeation flux. Further, the required gas amount (V ₁ ) needs to be determined in consideration of prevention of long-term deterioration of the membrane filtration characteristics.

The specific gas amount (V ₁ ) supplied below the flat plate-shaped membrane 4 is 0.5 ≦ V ₁ ≦ 380 per unit projected area and per unit time when the separation membrane is projected on the bottom surface of the purification tank.
(M ³ m ^-2 h ^-1 ). This is despite the scraping of the initial film surface sufficient in the amount of gas ^{200 (m 3 m -2 h -1} ), the time degradation prevention of membrane filtration properties over a long period of time 380 (m ³ m ^{- 2} h
^-1 ) or less gas amount is required, and even if a gas amount exceeding 380 (m ³ m ^-2 h ^-1 ) is supplied, the scraping effect of the filtration target layer does not change, and the gas amount is supplied. This is because power is wasted, and a gas amount smaller than 0.5 (m ³ m ^-2 h ^-1 ) cannot obtain the scraping effect by the bubble flow. Since there is a positive correlation between the gas amount and the rising rate of the bubbly flow due to aeration, the higher the gas amount, the higher the scraping efficiency obtained. However, since the power cost for that purpose and the scraping efficiency show a negative correlation, if the gas amount is too large, the power cost becomes excessive. Therefore, the upper limit of the desirable gas amount is 290 (m ³ m ^-2 h ^-1 ) in view of the balance between the membrane filtration characteristics and the power cost. The lower limit is 1.0 (m ³ m ^-2 h in order to obtain sufficient membrane filtration characteristics as a device.
^-1 ). That is, the desired gas amount (V ₁ ) is 1.0
≦ V ₁ ≦ 290 (m ³ m ⁻² h ⁻¹ )

Further, when only the aerobic treatment described above is performed, air may be continuously supplied from the air diffuser 7 toward the flat plate membrane 4, but anaerobic treatment, that is, acid production contained in activated sludge. Organic matter in the wastewater merged by the bacteria is converted into acetic acid (CH ₃
COOH), propionic acid (CH ₃ CH ₂ COOH), and other organic acids are converted into low molecular weight compounds, and these organic acids are converted to methane (CH ₄ ) and carbon dioxide (CO ₂ ) gas by methane bacteria. If you want to perform anaerobic treatment that produces ammonia nitrogen (NH ₄ ⁺ ), which is a decomposition product of nitrogen components such as protein and urea, do you supply oxygen-free gas such as nitrogen gas instead of air? Alternatively, when repeating the aerobic and anaerobic treatments, the air for aeration may be supplied intermittently.

Further, in the filtering method according to the second invention using the filtering device 3, air is supplied toward the plate-shaped membrane 4 from both the first air diffusing tube 7 and the second air diffusing tube 8. Then, as described above, not only the bubble flow along the surface of the flat plate-shaped film 4 is formed, but also the bubbles from the second diffusing tube 8 directly contact the surface of the flat plate-shaped film 4 and are vibrated or shocked to form a flat plate-shaped film. The activated sludge 10 or the like adhering to the surface of the membrane 4 is peeled off.

As described above, the separation action is dramatically improved as compared with the first invention by applying not only the bubble flow but also vibration and impact. However, the amount of gas (V ₂ ) at which such a dramatic effect can be expected is V ₂ ≦ 2000 (m ³ m ⁻² h ⁻¹ ) per unit area of the separation membrane and per unit time. This is because the peeling effect is not improved even if a larger amount is supplied, and V ₂ ≦ 500 (m ³ m ⁻² h ⁻¹ ) is preferable.

FIG. 5 is a vertical cross-sectional view of a septic tank in which a filtering device according to the fourth invention of the present application is incorporated, FIG. 6 is a view seen from the direction BB of FIG. 5, and FIG. 7 is an enlarged view of the main part of FIG. In this septic tank, the inside of the septic tank main body 1 is divided into two processing chambers by the partition wall 12, and the filtration device 13 is arranged in one of the processing chambers.

The filtering device 13 has a water collecting pipe 15 attached to an upper portion of a holding frame 14, a suction pipe 17 connected to a pump 16 is connected to the water collecting pipe 15, and a gas ejection hole 18a is downwardly directed to a lower portion of the holding frame 14. Is attached to the air diffuser 18. Then, the hollow fiber membrane 19 as a separation membrane is folded back so that both ends are upward, both ends thereof are connected to the water collecting pipe 15, and an air diffuser pipe 18 is arranged at the folded portion, and the hollow fiber membrane 19 is arranged at the lower end of the hollow fiber membrane 19. Air is supplied to form a bubble flow along the hollow fiber membranes 19 in the vertical direction and to give vibrations to the hollow fiber membranes 19. Here, since the hollow fiber membrane is used as the separation membrane, the membrane itself is moved by the gas, and the layer of the substance to be filtered is effectively separated due to fluctuation.

FIG. 8 is a vertical cross-sectional view of a septic tank incorporating the filtering device according to the fifth aspect of the present invention. In the septic tank, two filtering devices 20 are arranged in parallel in the septic tank body 1. The filtration device 20 has two water collecting pipes 21 spaced apart from each other in the main body 1, and both ends of a hollow fiber membrane 22 which is laterally installed between the two water collecting pipes 21 are connected to the water collecting pipe 21. The suction pipe 24 connected to the pump 23 is connected to the water collection pipe 21.
And an air diffuser 25 is arranged below the hollow fiber membrane 22.

In the filtration device 20 shown in FIG. 8, since the hollow fiber membrane 22 is laid horizontally (or diagonally), the hollow fiber membrane is formed by the bubble flow formed by the gas supplied from the diffuser pipe 25. Since the membrane 22 vibrates, the peeling of the filtration target layer 11 is extremely remarkable due to the synergistic effect of the scraping action by the bubble flow and the vibration.

[0027]

As described above, according to the filtration method according to the first invention of the present application, the bubble flow in which the stock solution and the gas are mixed along the separation membrane in order to separate the layer to be filtered accumulated on the surface of the separation membrane. Are formed continuously or intermittently, and the amount of gas (V
₁ ) is per unit projected area of the separation membrane and per unit time,
Since 0.5 ≦ V ₁ ≦ 380 (m ³ m ⁻² h ⁻¹ ) is set, the layer to be filtered can be efficiently peeled off.

Further, according to the filtration method of the second invention of the present application, not only the bubble flow but also the bubbles are applied to the surface of the separation membrane. Therefore, the synergistic effect of the scraping action by the bubble flow and the vibration action by the bubbles is achieved. It is possible to more efficiently peel the layer to be filtered. In particular, this effect is achieved by changing the amount of gas (V ₂ ) supplied per unit area of the separation membrane and per unit time,
It becomes remarkable when V ₂ ≦ 2000 (m ³ m ⁻² h ⁻¹ ).

According to the filtration device of the third aspect of the present invention, the separation membrane is a flat plate membrane arranged vertically in the stock solution, and the stock solution is placed below the flat plate membrane along the flat plate membrane. Since the air diffuser for forming the bubble flow mixed with the gas is arranged, and the air diffuser for applying the air bubbles to the flat plate-shaped film is arranged on the side of the flat plate-shaped film, the scraping action by the bubble flow and The substance layer to be filtered can be peeled off by the synergistic effect of the vibration action of the bubbles.

Further, according to the filtration device of the fourth aspect of the present invention, the separation membrane is a hollow fiber membrane which is vertically installed in the stock solution, and the hollow fiber membrane is folded back so that both ends thereof are upward. Since it is connected to the water member and the diffusing member is arranged at the folded back portion, an efficient scraping action due to the bubble flow can be exhibited, and the diffusing member also functions as a supporting member for the hollow fiber membrane. , The structure is simple.

Furthermore, according to the filtration device of the fifth aspect of the present invention, the separation membrane is a hollow fiber membrane horizontally laid in the stock solution, and both ends of this hollow fiber membrane are connected to a water collecting member, Since the air diffuser is arranged below the hollow fiber membrane, the peeling action by vibration becomes extremely large in addition to the scraping action by the bubble flow.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a septic tank incorporating a filtration device according to a third invention of the present application.

FIG. 2 is a view seen from the direction AA of FIG.

FIG. 3 is a diagram explaining the operation of the present invention.

FIG. 4 is a graph of experimental results showing how the membrane permeation flux changes with the passage of filtration time depending on the amount of gas.

FIG. 5 is a vertical cross-sectional view of a septic tank incorporating a filtration device according to a fourth aspect of the present application.

FIG. 6 is a view seen from the direction BB of FIG.

7 is an enlarged view of a main part of FIG.

FIG. 8 is a vertical cross-sectional view of a septic tank in which a filtration device according to a fifth invention of the present application is incorporated.

[Explanation of symbols]

1 ... Main body of septic tank, 2, 12 ... Partition walls, 3, 13, 20 ...
Filtration device, 4 ... Flat plate membrane, 5, 16, 23 ... Pump,
6, 17, 24 ... Suction tube, 7, 8, 18, 25 ... Air diffuser tube, 10 ... Activated sludge particles, 11 ... Filtered material layer, 15, 2
1 ... Water collecting pipe, 19, 22 ... Hollow fiber membrane.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Urushi Katsushi 2-1-1 Nakajima, Kokurakita-ku, Kitakyushu-shi, Fukuoka Prefecture Totoki Kikai Co., Ltd. (72) Yuichi Okuno Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka 2-1, 1-1 Totoki Equipment Co., Ltd.

Claims (6)

[Claims] 1. A filtration method in which a separation membrane is immersed in an undiluted solution and filtration is carried out. In this filtration method, the undiluted solution and the gas are separated along the separation membrane in order to separate a layer to be filtered deposited on the surface of the separation membrane. To form a mixed bubble flow continuously or intermittently, and the amount of gas (V ₁ ) supplied below the separation membrane to form the bubble flow is per unit projected area of the separation membrane and in units. 0.5 ≤ V ₁ ≤ 380 (m ³ m per hour
^-2 h ^-1 ). 2. A filtration method in which a separation membrane is immersed in an undiluted solution and filtration is carried out. In this filtration method, the undiluted solution and the gas are separated along the separation membrane in order to remove the layer to be filtered accumulated on the surface of the separation membrane. The method of filtration is characterized in that the mixed bubble flow is formed continuously or intermittently, and the bubbles are continuously or intermittently applied to the layer to be filtered on the surface of the separation membrane. 3. The filtration method according to claim 2, wherein the amount of gas (V) supplied near the surface of the separation membrane to form the bubble flow and to form bubbles that contact the surface of the separation membrane.
₂ ) is V ₂ per unit area and unit time of the separation membrane.
≦ 2000 (m ³ m ⁻² h ⁻¹ ) The filtration method, wherein 4. A filtration device for filtering a stock solution by means of a separation membrane, wherein the separation membrane is a flat plate membrane arranged vertically in the stock solution, and below the flat plate membrane, along the flat plate membrane. An air diffuser for forming a bubble flow in which the stock solution and the gas are mixed is arranged, and an air diffuser for applying bubbles to the flat film is arranged on the side of the flat film. Filtering device. 5. A filtration device for filtering a stock solution by a separation membrane, wherein the separation membrane is a hollow fiber membrane laid vertically in the stock solution, and the hollow fiber membrane is folded back so that both ends thereof are upward. The filtration device is characterized in that both ends thereof are connected to a water collecting member, and an air diffuser member is arranged at the folded portion. 6. A filtration device for filtering a stock solution with a separation membrane, wherein the separation membrane is a hollow fiber membrane laterally installed in the stock solution, and both ends of the hollow fiber membrane are connected to a water collecting member, Further, the filter device is characterized in that an air diffusing member is arranged below the hollow fiber membrane.