JPH0824594A - Operation of filter - Google Patents

Abstract

PURPOSE:To restore the effective membrane area by disaggregating the hollow- fiber membranes and to secure a fixed permeation flux by specifying the suction pressure acting on the hollow-fiber membrane dipped in the waste water in a septic tank. CONSTITUTION:A hollow-fiber membrane is dipped in the waste water in a septic tank to filter the waste water. In this case, the suction pressure acting on the membrane is controlled to <=0.8kgf/cm<2>, and the membranes are disaggregated to restore the effective membrane area during filtration operation. The aggregation of the membranes depends on the suction pressure, filtration condition and physical properties of the liq. For example, when the air is diffused from below the membrane to fluidize the waste water on the membrane surface in filtration, the membranes are aggregated at about 0.4kgf/cm<2> suction pressure when the amt. of the air diffused is small, however aggregation is not caused even at a higher pressure when more air is diffused, and aggregation tends to be caused at >=0.8kgf/cm<2> even if the liq. properties and filtration conditions are adjusted.

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. For example, as a septic tank for biologically treating wastewater from households such as toilets, washrooms, baths and kitchens, industrial wastewater, etc., Japanese Patent Application No. 4-131182.
Some are disclosed in Japanese Patent Publication. In this prior art, the separation membrane is immersed in a septic tank, and the wastewater that has undergone biological treatment has a permeate that does not contain activated sludge and a retentate that contains activated sludge (concentrated liquid).
It is separated (filtered) into and and the permeated liquid is discharged. Then, a hollow fiber membrane is used as a separation membrane, and a cake layer deposited on the surface of the hollow fiber membrane by turbulent flow due to aeration is removed, and back pressure cleaning using a chemical solution is also described.

[0003]

When a membrane module is composed of hollow fiber membranes, the membrane area required for filtration operation in a unit volume is greatly advantageous as compared with other tubular membranes or flat membranes. There is a problem peculiar to the hollow fiber membrane as described in.

FIG. 1 is a graph showing the relationship between the elapsed time of filtration operation using a hollow fiber membrane and the permeation flux, and FIG. 2 is the steady state of the suction pressure (transmembrane pressure difference) acting on the separation membrane and the permeation flux. It is a graph which shows the relationship with a value. As can be seen from the graph of FIG. 1, after about 2 hours from the start of the filtration operation, the cake layer deposited on the membrane surface and the cake layer separated from the membrane surface were balanced, and the permeation flux became a steady value (Jss). Become. This tendency is not limited to hollow fiber membranes and is the same for tubular membranes and flat membranes.

However, as can be seen from the graph of FIG. 2, the hollow fiber membrane exhibits different characteristics from other membranes depending on the magnitude of suction pressure. That is, in the first region where the suction pressure is small, the relationship between the suction pressure (ΔP) and the steady value of the permeation flux (Jss) is linear and proportional regardless of the shape of the membrane. The steady-state value (Jss) of the permeation flux becomes constant regardless of the shape of the membrane in the second region where the suction pressure is large to some extent, and the steady-state value (Jss) decreases only in the hollow fiber membrane in the third region where the suction pressure is large. To do.

As described above, the steady-state value (Jss) of only the hollow fiber membranes in the third region decreases as shown in the schematic diagram for reference in the same graph. However, the plurality of hollow fiber membranes constituting the membrane module are separated from each other, but it is considered that when the suction pressure becomes strong, the plurality of hollow fiber membranes aggregate to reduce the effective membrane area involved in filtration.

[0007]

In order to solve the above-mentioned problems, the present invention immerses a hollow fiber membrane in waste water in a septic tank, sucks the secondary side of this hollow fiber membrane, and retains the waste water as a permeate. In a method for operating a septic tank adapted to be filtered with a liquid (concentrated liquid), the suction pressure is set to 0.8 kgf / cm ² or less, and an effective membrane area recovery operation for releasing aggregation of hollow fiber membranes during the filtration operation To do.

Here, the agglomeration of the hollow fiber membrane is caused by the suction pressure (Δ
P), it varies depending on the filtration operation conditions such as the flow state of waste water on the membrane surface and the liquid physical properties such as the MLSS concentration. For example, when the air flow from the lower part of the membrane is used as shown in Fig. 2 for the flow of wastewater on the membrane surface during the filtration operation, if the amount of air diffusion is small as shown in Fig. 2, it aggregates at about 0.4 kgf / cm ^2. However, when the amount of air diffused is increased, aggregation does not occur even at a higher suction pressure. However, when the suction pressure is higher than 0.8 kgf / cm ^2, agglomeration is likely to occur even if the liquid physical properties or the filtration operation conditions are adjusted, for example, the MLSS is decreased or the aeration amount is increased. Therefore, the suction pressure should be 0.8kgf / cm.
² or less.

When performing filtration operation using a hollow fiber, a diffusing device or the like is used, and a gas-liquid two-phase flow or a gas-liquid solid three-phase flow is made to flow along the surface of the hollow fiber membrane to thereby produce a hollow fiber. It is preferable to scrape off the cake layer deposited on the film surface.

When the gas-liquid two-phase flow or gas-liquid solid three-phase flow is formed, if the sludge concentration (MLSS) becomes too high, the permeation flux decreases, so the sludge concentration (MLSS).
Is 30 kg / m ³ or less as the dry weight concentration at 110 ° C,
Further, it is preferably 20 kg / m ³ or less in consideration of the wash recoverability.

The amount of gas (m ³ ) supplied to form the gas-liquid two-phase flow is 1.0 to 380 per unit time and the projected area of the hollow fiber membrane on the bottom surface of the tank filled with the stock solution.
m ³ / (m ² · h) If this is less than 1.0 m ³ / (m ² · h), the coagulation of the hollow fiber membrane gradually progresses, and after exceeding 380 m ³ / (m ² · h), the scraping effect hardly increases, so the cost is low. It will be disadvantageous. From the above viewpoint, the preferable range is 5.0 to 250 m ³ / (m ² · h).

The average diameter of the particles added to form the gas-liquid solid three-phase flow is 0.01 to 50 mm, and the amount of gas supplied (m ³ ) is the hollow fiber with respect to the bottom of the tank filled with the stock solution. 2.0 to 400 m ³ per projected area of the film and per unit time
/ (m ² · h) The average diameter of the particles mentioned here is the diameter when the accumulation of particles is converted into spheres. And when the average diameter of the particles is set to 0.01 to 50 mm, when the particle diameter is smaller than 0.01 mm, the added particles themselves are taken into the cake layer, rather the permeation resistance increases and the permeation flux decreases, and when the particle diameter exceeds 50 mm. This is because the particles collide excessively with each other, the fluidity decreases, and the scraping effect decreases. The preferable average diameter of the particles is 0.1 to 10 mm.

On the other hand, as the effective membrane area recovery operation,
A method of diffusing air from an air diffusing device arranged below the hollow fiber membrane, a method of directly applying gas from a diffusing means arranged on the side of the hollow fiber membrane toward the surface of the hollow fiber membrane, and a hollow fiber by mechanical means. There is a method of applying vibration to the membrane.

And the amount of air diffused by air diffusion (m ³ )
Is 20 to 800 m ³ / (m ² · h) per projected area of the hollow fiber membrane on the bottom surface of the tank filled with the stock solution and per unit time. If it is less than 20 m ^3, it has no effect, and if it exceeds 800 m ³ , it is sufficient to break the agglomeration, but energy is wasted. A preferable range is 50 to 500 m ³ /
(m ² · h). The amount of gas when the gas is directly applied to the surface of the hollow fiber membrane is 0.05 to 90 m ³ / (m ² · h) per unit area of the hollow fiber membrane and per unit time. This is also for the same reason as above, and the preferable range is 0.1 to 10.
It is 30 m ³ / (m ² · h). Further, the range of vibration given by mechanical means is 0.1 to 180 Hz. This is because there is no effect when the frequency is less than 0.1 Hz, and the strength of the film decreases when the frequency exceeds 180 Hz.

Further, the switching between the filtration operation and the effective membrane area recovery operation includes a method by a timer, a method by which the transmembrane pressure difference is detected, and a method by which a decrease in the permeation flux of the hollow fiber membrane is detected.

In the method of switching by a timer, the ratio of the filtration operation time to the effective membrane area recovery operation time (filtration operation time / effective membrane area recovery operation time) is 1 to 660,
It is preferably 2.5 to 150. This is because if the above ratio is too small, the filtration efficiency decreases, and if it is too large, the agglomeration becomes strong and the agglomeration becomes difficult to release. In addition, in the method of detecting transmembrane pressure difference, 0.3 to 0.8 kgf / cm
Detection is performed within the range of ² . This is 0.3 kgf / cm ²
If it is less than 0.8 kg, the filtration efficiency is poor, and if it exceeds 0.8 kgf / cm ² , aggregation is likely to occur. Further, in the method of detecting a decrease in permeation flux, it is preferable to start the effective membrane area recovery operation at the time when the permeation flux decreases by 10% from the steady value. This means that the permeation flux is 10
When it is decreased by more than%, a large amount of energy is required to release the agglomeration.

[0017]

By performing the effective membrane area recovery operation for releasing the aggregation of the hollow fiber membranes during the filtration operation, the continuous filtration operation maintaining the permeation flux becomes possible.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 3 is a cross-sectional view showing an example of a septic tank to which the operating method of the filtration device according to the present invention is applied, and FIG.
(A)-(c) is a figure showing other examples of a hollow fiber membrane module, Drawing 5 is a sectional view showing other examples of the same septic tank, and Drawing 6 is a sectional view showing other examples of the same septic tank.

Waste water 3 is supplied into the septic tank 1 through an introduction pipe 2, a partition wall 4 is arranged in the septic tank 1, a membrane module 5 is arranged in the partition wall 4, and the membrane module 5 is arranged.
An air diffuser 6 is provided below the. As the septic tank, not only the biological reaction chamber but also one provided with a flow rate adjusting unit, or the biological reaction chamber divided into an aerobic treatment chamber and an anaerobic treatment chamber may be used.

The membrane module 5 has a hollow fiber membrane 7 which is a separation membrane, and a water collecting portion 8 to which the upper ends of the hollow fiber membranes 7 are connected.
The suction pipe 9 is connected to the water collecting part 8 and the suction pump 10 is driven to exert a negative pressure on the secondary side of the hollow fiber membrane 7 to convert the biologically treated wastewater 3 into activated sludge. It is filtered (separated) into a permeated liquid not containing it and a retentate (concentrated liquid) having a high activated sludge concentration, and the permeated liquid is discharged to the outside through the water collecting section 8 and the suction pipe 9.

Here, the steady-state value of the permeation flux is (Jss)
= Kφu ^{* 1.0} (MLSS) ^−0.5 .
K is a filtration constant calculated as 2.6 x 10 ^-5 kg ^0.6 m ^-1.5, and φ
Is the shape factor (Jss of hollow fiber membrane) / (Js of ideal state)
s), where u ^* is the apparent membrane surface velocity, which converts the upward flow due to aeration to u ^* . The diameter of the membrane module 5 is 0.8.

The sludge concentration (MLSS) in the wastewater is
The dry weight concentration at 110 ° C. is 30 kg / m ³ or less, preferably 20 kg / m ³ or less, and the amount of gas supplied to form the gas-liquid two-phase flow is per unit projected area of the hollow fiber membrane on the bottom of the septic tank and 1.0 to 380 m ³ / (m ² · per unit time
h), preferably 5.0 to 250 m ³ / (m ² · h), and the average diameter of particles added to form a gas-liquid three-phase flow is 0.0
It is 1 to 50 mm, preferably 0.1 to 10 mm, and the amount of gas supplied is 2.0 to 400 m ³ / (m ² · h) per projected area of the hollow fiber membrane on the bottom of the septic tank and per unit time.

In this embodiment, not only the filtration operation is performed by forming a gas-liquid two-phase flow or a gas-liquid solid three-phase flow along the surface of the hollow fiber membrane 7 by air diffusion from the air diffusing pipe 6. During the stoppage of the filtration operation, an effective membrane area recovery operation is performed in which the agglomeration of the hollow fiber membranes is released by the air diffused from the air diffuser 6. Aeration amount at this time and per unit time 20~800m ³ / per projected area of the hollow fiber membrane (m ² · h) for the septic tank bottom, preferably ^{50~500m 3 / (m 2 · h} ).

The following (Table 1) shows the MLSS concentration of 10 kg / m.
³ , the amount of air diffused to form gas-liquid two-phase flow is 15m ³ / (m ² ·
h) shows the experimental results of the recovery rate when the suction pressure was 0.5 kgf / cm ² and the amount of air diffused for the effective membrane area recovery operation was changed. The effective membrane area recovery operation is filtration 1
After repeating 0 times, it was performed for 30 minutes, and the recovery rate was evaluated as the ratio of the initial membrane permeation flux to the membrane permeation flux immediately after the recovery operation. From this (Table 1), it is understood that the aeration amount should be in the above range.

[0025]

[Table 1]

The type of the membrane module 5 is shown in FIG.
What is shown in (a)-(c) may be sufficient. Figure 4 (a)
In the membrane module 5 shown in (1), a plurality of hollow fiber membranes 7 hanging from the water collecting portion 8 are spread in a skirt shape, and φ of this membrane module 5 is 0.9. In the membrane module 5 shown in FIG. 4 (b), the plurality of hollow fiber membranes 7 hanging from the water collecting portion 8 has a larger spread than that shown in FIG. 4 (a), and φ of this membrane module 5 is 1.0. is there. The membrane module 5 shown in FIG. 4 (c) has a plurality of hollow fiber membranes 7 hanging from a tubular water collecting portion 8 in a curtain shape, and φ of this membrane module 5 is 1.
0.

5 and 6 are sectional views showing another embodiment of the same septic tank. In the other embodiment shown in FIG. 5, the air diffuser 6 is shown.
Separately from the hollow fiber membrane 7, an air diffuser 11 is arranged, and the gas is directly applied from the air diffuser 11 toward the surface of the hollow fiber 7 to recover the effective membrane area of the hollow fiber 7. I am trying. The amount of gas when the gas is directly applied to the surface of the hollow fiber membrane is 0.05 to 90 m ³ / (m ² · h) per unit area of the hollow fiber membrane and preferably 0.1.
-30 m ³ / (m ² · h)

In another embodiment shown in FIG. 6, two water collecting portions 8 in which the membrane module 5 is arranged in the longitudinal direction and a plurality of hollow fibers horizontally laid between the water collecting portions 8 are provided. A bar 13 which is composed of the membrane 7 and which is cranked by a motor 12 is arranged above the septic tank 1. An elevating member 14 is connected to the bar 13 and the elevating member 14 is interlocked with the crank movement of the bar 13.
Moves up and down to shake the hollow fiber membrane 7 to perform an effective membrane area recovery operation. The range of vibration given to the hollow fiber membrane 7 by the above crank movement is 0.1 to 180 Hz.

The operation method of the septic tank according to the present invention will be described below with reference to FIG. First, the suction pump 10 is driven to perform a filtration operation. This filtration operation is performed intermittently, and after the filtration operation is stopped, back pressure washing is performed for a short time to recover the permeation flux. When the filtration operation and the back pressure washing are alternately and continuously performed, the hollow fiber membranes are gradually aggregated and the permeation flux cannot be recovered even if the back washing is performed. Therefore, the filtration operation is suspended for a certain length of time, and during this period, an effective membrane area recovery operation for releasing the aggregation of the hollow fiber membranes is performed.

Switching between the filtration operation and the effective membrane area recovery operation includes a method by a timer, a method by which the transmembrane pressure difference is detected, and a method by which a decrease in the permeation flux of the hollow fiber membrane is detected. In the method of switching by a timer, the ratio of the filtration operation time to the effective membrane area recovery operation time (filtration operation time / effective membrane area recovery operation time) is 1 to 660, preferably 2.5 to 1
Set to 50. Further, in the method of detecting the transmembrane pressure difference, the detection is performed within the range of 0.3 to 0.8 kgf / cm ² . Further, in the method of detecting the decrease in permeation flux, the effective membrane area recovery operation is started at the time when the permeation flux decreases by 10% from the steady value.

In the following (Table 2), the amount of air diffused for the effective membrane area recovery operation is 100 m ³ / (m ² · h), and other conditions are the same as those obtained in the above (Table 1). The experimental result of the relationship between the reduction rate from the steady value of the membrane permeation flux and the recovery rate at the time of starting the effective membrane area recovery operation in the case of performing as above is shown. The steady value of the membrane permeation flux is (Jss) = Kφu ^{* 1.0} (MLS
S) Calculated from ^-0.5 .

[0032]

[Table 2]

As can be seen from this (Table 2), when the effective membrane area recovery operation is started after the permeation flux is reduced by 10% or more from the steady value, the recovery rate becomes poor. It requires more energy than the recovery operation. Therefore, as described above, the permeation flux is 10
It is preferable to start the effective membrane area recovery operation before it decreases by more than 0.1%.

[0034]

As described above, according to the present invention, the suction pressure acting on the hollow fiber membrane by immersing it in the waste water in the septic tank is set to 0.8 kgf / cm ² or less, so that the hollow fiber membranes are aggregated. Can be suppressed. Further, since the effective membrane area recovery operation for releasing the agglomeration of the hollow fiber membranes is performed during the filtration operation, a constant permeation flux can be secured. Further, by flowing a gas-liquid two-phase flow or a gas-liquid solid three-phase flow along the hollow fiber membrane surface, the cake layer deposited on the hollow fiber membrane surface can be scraped off.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the elapsed time of filtration operation and the permeation flux.

FIG. 2 is a graph showing a relationship between a suction pressure (transmembrane pressure difference) acting on a separation membrane and a steady value of a permeation flux.

FIG. 3 is a cross-sectional view showing an example of a septic tank to which the method for operating a filtration device according to the present invention is applied.

4A to 4C are views showing another embodiment of the hollow fiber membrane module.

FIG. 5 is a cross-sectional view showing another embodiment of the septic tank.

FIG. 6 is a cross-sectional view showing another embodiment of the septic tank.

FIG. 7 is a graph showing a pattern of a method for operating a septic tank according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Septic tank (filtering device), 2 ... Introducing pipe, 3 ... Waste water (stock solution), 5 ... Membrane module, 6 ... Air diffuser, 7 ... Hollow fiber membrane,
8 ... Water collecting part, 9 ... Suction pipe, 10 ... Suction pump, 11 ... Air diffuser, 12 ... Motor, 13 ... Bar, 14 ... Elevating member.

 ─────────────────────────────────────────────────── ─── 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 (17)

[Claims] 1. A filtration in which a hollow fiber membrane is immersed in a stock solution in a filtration device, the secondary side of the hollow fiber membrane is sucked, and the stock solution is filtered into a permeate and a retentate (concentrate). In the method for operating the device, the suction pressure is 0.8 kgf / cm ² or less, and further, an effective membrane area recovery operation for releasing aggregation of the hollow fiber membranes during the filtration operation is performed. Driving method. 2. The method of operating a filtration device according to claim 1, wherein a cake deposited on the surface of the hollow fiber membrane by flowing a gas-liquid two-phase flow or a gas-liquid solid three-phase flow along the surface of the hollow fiber membrane. A method for operating a filtration device, wherein the layer is scraped off. 3. The method for operating a filtration device according to claim 1, wherein the effective membrane area recovery operation is performed by air diffusion from an air diffusion device disposed below the hollow fiber membrane. And a method for operating a filtration device. 4. The method of operating the filtration device according to claim 3, wherein the air diffusion amount (m ³ ) is 20 to 20 per unit time per projected area of the hollow fiber membrane on the bottom surface of the tank filled with the stock solution.
A method of operating a filtration device, which is 800 m ³ / (m ² · h). 5. The method for operating a filtration device according to claim 1 or 2, wherein the effective membrane area recovery operation is performed from an air diffuser disposed laterally of the hollow fiber membrane toward the surface of the hollow fiber membrane. A method for operating a filtration device, which is characterized in that a gas is directly applied. 6. The method for operating a filtration device according to claim 5, wherein the gas amount (m ³ ) supplied from the air diffusing means is 0.05 to 90 per unit area of the hollow fiber membrane and per unit time.
A method of operating a filtration device, characterized in that m ³ / (m ² · h). 7. The method for operating a filtration device according to claim 1 or 2, wherein the effective membrane area recovery operation is performed by vibrating the hollow fiber membrane by mechanical means. Driving method. 8. The method for operating the filtration device according to claim 7, wherein the vibration applied to the hollow fiber membrane is 0.1 to 180 H.
A method of operating a filtration device characterized in that it is z. 9. The method for operating a filtration device according to claim 1, wherein the switching between the filtration operation and the effective membrane area recovery operation is performed by a timer. how to drive. 10. The method for operating a filtration device according to claim 9, wherein the ratio of the filtration operation time to the effective membrane area recovery operation time (filtration operation time / effective membrane area recovery operation time) is 1.
The method for operating a filtration device is characterized in that 11. The method for operating a filtration device according to claim 1 or 2, wherein the effective membrane area recovery operation is performed by detecting a transmembrane pressure difference. how to drive. 12. The method of operating a filtration device according to claim 11, wherein the detected transmembrane pressure difference is 0.3 to 0.8.
A method for operating a filtration device, wherein the value is within a range of kgf / cm ² . 13. The method for operating a filtration device according to claim 1, wherein the effective membrane area recovery operation is performed by detecting a decrease in permeation flux of the hollow fiber membrane. How to operate the device. 14. The method of operating a filtration device according to claim 13, wherein the effective membrane area recovery operation is started when the permeation flux is reduced by 10% from a steady value. Method. 15. The method of operating a filtration device according to claim 2, wherein the sludge concentration (MLSS) in the stock solution is 110.
A method for operating a filtration device, wherein the dry weight concentration at 30 ° C. is 30 kg / m ³ or less. 16. The method of operating a filtration device according to claim 2, wherein the gas amount (m ³ ) supplied to form the gas-liquid two-phase flow is a hollow fiber membrane with respect to the bottom surface of the tank filled with the stock solution. Per projected area and per unit time 1.0 to 380 m ³ /
(m ² · h) The method for operating the filtration device. 17. The method for operating a filtration device according to claim 2, wherein the particles added to form the gas-liquid solid three-phase flow have an average diameter of 0.01 to 50 mm, and the amount of gas supplied (m ³ ) is 2.0 to 400 m ³ / (m ² per unit time per projected area of the hollow fiber membrane on the bottom of the tank filled with the stock solution.
・ A method of operating a filtration device characterized in that