JPH06319958A - Operating method for flat membrane type filter - Google Patents

Abstract

PURPOSE:To supply filtering liquid stable in flow rate over a long period of time by a method wherein the flow rate of operating filtering liquid is set at a low flow rate in relation to the flow rate of pure water filtered under a specific difference in pressure between membranes. CONSTITUTION:Raw liquid is supplied into a liquid treating tank 41 by operating a raw material feed pump 43, a vacuum pump 45 is operated to reduce the pressure on the filtering side of a flat type filter membrane cell A so as to cause the difference in pressure between membranes necessary for the filtering and the initial rate of permeating flow is set at a predetermined value within the range of 1-5% of the amt. of pure water permeating under a pressure difference of 1kg/cm<2> between the membranes. And the filtration is allowed to proceed under this pressure difference between the membranes and the raw liquid is fed continuously or intermittently in a rate of flow almost equal to the rate of permeating flow and is treated while its level in the liquid treating tank 41 is kept almost constant. A blower 49 is operated at predetermined intervals for predetermined periods of hour in order to diffuse air from an air diffusing pipe 48 and pass it through a gap between the material passages of the flat type filter membrane cell A, so that the membrane surface is cleaned by air scrubbing.

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 flat sheet membrane type filtration device capable of supplying a filtrate at a stable flow rate for a long period of time.

[0002]

2. Description of the Related Art Recently, a membrane filtration device using a microfiltration membrane, an ultrafiltration membrane or the like is often used for the purification, concentration and recovery of valuable materials of a stock solution. In this membrane filtration device, a decrease in the filtrate flow rate due to membrane contamination is unavoidable, and particularly in the full-volume filtration system, the decrease in the filtrate flow rate is remarkable. Therefore, in the stock solution treatment by the membrane filtration device,
It is indispensable to perform membrane cleaning regularly to prevent the permeate flow rate from decreasing.

Although various methods have been proposed for this membrane cleaning method, an air scrubbing method (air is diffused from an air diffuser into the stock solution and a mixed fluid of the diffused air and the stock solution is brought into contact with the membrane surface). In the method), the membrane can be washed while performing filtration, which is advantageous.

Although various types of membrane filtration devices have been developed, among the flat membrane filtration devices, a plurality of flat filtration membrane cells having a filtration liquid flow path inside the membrane are treated. Unlike the spiral type, the air scrubbing cleaning is possible in the case where the stock solution is erected in the tank with a gap between the stock solution channels.

[0005]

However, according to the experiments conducted by the present inventors, when the flat membrane type filtration device is subjected to air scrubbing cleaning, air is removed in order to prevent the physical strength of the membrane from decreasing. -It is necessary to set the flow rate to 0.1-2 Nm ³ / h per 1 m ² of membrane area. However, in air scrubbing under such conditions, the filtration resistance increases considerably over time, and even if the average flow rate of the filtrate can be increased,
The flow rate of the filtrate is significantly reduced, and it is difficult to supply the filtrate at a stable flow rate.

An object of the present invention is to provide a flat sheet membrane filtration device,
It is an object of the present invention to provide a method for operating a flat sheet membrane filtration apparatus capable of supplying a filtrate at a stable flow rate for a long period of time.

[0007]

The method for operating a flat sheet membrane filtration apparatus of the present invention is a method for filtering a stock solution using a flat sheet membrane cell having a filtrate channel inside a membrane. The liquid flow rate is set to a constant value within 1% to 5% of the filtration flow rate of pure water under a transmembrane pressure difference of 1 kg / cm ² .

[0008]

[Operation] The operating filtrate flow rate is set to a low flow rate of 1% to 5% with respect to the filtration flow rate of pure water under a transmembrane pressure difference of 1 kg / cm ² . The increase rate of the solute concentration becomes slower, the increase in filtration resistance due to the solute distribution on the membrane surface is alleviated, and the decrease in the filtrate flow rate is alleviated accordingly. Therefore, the decrease in the flow rate of the filtrate can be suppressed, and the stable supply of the filtrate can be achieved.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a flat sheet membrane filtration device used in the present invention. In FIG. 1, A represents a laminated structure of flat filtration membrane cells, and a flat filtration membrane cell single body 1 having a filtrate flow channel inside the membrane is separated from each other as shown in FIG. Are stacked while holding the undiluted solution flow path gap 2 therein, frame edges 31 are attached to both ends of the laminated body, and partition walls 32 are formed by injecting resin into each frame edge 31, and each frame edge 31 is sealed. A filtrate removing cap 34 is attached in a watertight manner through a tongue-shaped packing 33 (the dimensions are usually 10 to 200 cm in width and 3 to in length).
(About 150 cm).

In FIG. 1, reference numeral 41 denotes an open type liquid tank for treatment in which the flat-type filtration membrane cell laminated structure A is vertically housed and dipped and housed. Reference numeral 42 is a stock solution supply pipe, and 43 is a stock solution supply pump. 44 is a filtered liquid extraction pipe, 45 is a vacuum pump,
46 is a flow meter and 47 is a filtrate storage tank. Reference numeral 48 is an aeration pipe arranged immediately below the flat filtration membrane cell laminated structure A, 4
9 is a blower.

As shown in FIG. 2B, the flat filtration membrane cell simple substance 1 is provided with a filtrate liquid flow path holding member (for example, polyolefin such as polyethylene, net such as vinyl chloride, porous plastic sheet). And the like) on both sides of the semipermeable flat membrane (polyester or polyethylene non-woven fabric material such as polysulfone, polyethersulfone,
A film layer formed of polyacrylonitrile, polyvinyl alcohol, polyethylene or the like, or a film layer in which a polyester or polyethylene woven fabric is embedded can be used.) 12 is attached, and the upper and lower edges are adhesive. Those sealed with 13 can be used. Further, for the partition wall 32 in the frame 31, a curable resin such as an epoxy type, a urethane type, or a silicone type can be used.

In order to operate this flat sheet membrane filtration apparatus according to the present invention, in FIG. 1, the stock solution is fed into the liquid tank 41 to be treated by driving the stock solution feed pump 43, and the vacuum pump 45 is driven to drive the flat plate filtration apparatus. The pressure on the filtration side of the membrane cell A is reduced to generate the transmembrane pressure difference necessary for filtration, and the initial flow rate is set to the pure water filtration flow rate (referred to as pure water permeated water amount) at the transmembrane pressure difference of 1 kg / cm ^2. The transmembrane pressure is adjusted so that the permeation flow rate becomes a predetermined value within 1 to 5% of the pure water permeation flow rate, filtration is advanced under the transmembrane flow rate, and the flow rate is almost equal to this filtration flow rate. The stock solution is continuously or intermittently supplied, and the stock solution is processed while maintaining the water level of the stock solution in the liquid tank 41 to be treated almost constant.

In parallel with this filtering process, the blower 49 is driven for a certain period of time for a certain period of time to diffuse the air from the diffuser pipe 48 and raise the mixed fluid of the diffused air and the stock solution. The membrane surface is subjected to air scrubbing cleaning by passing through the gap of the undiluted solution flow path of the mold filtration membrane cell A.

As is well known, the transmembrane pressure difference is Δp, the filtration resistance of the membrane itself is Rm, and the filtration resistance based on the solute concentration on the membrane surface is Rc.
Then, the filtration flow rate J is given by J = Δp / (Rm + Rc). In the method for operating the flat sheet membrane filtration apparatus of the present invention, the initial filtrate flow rate is set to a remarkably low value within 1 to 5% of the pure water permeate amount, so that the solute concentration on the membrane surface is significantly increased. It can be made slow, the increase of Rc with time can be sufficiently suppressed, and the above J can be made sufficiently constant despite the passage of time.

In the present invention, the reason why the operating filtrate flow rate (initial filtrate flow rate) is set within 1 to 5% of the pure water permeated water amount is that the filtration resistance based on the solute concentration on the membrane surface is 5% or more. This is because the increase in Rc over time becomes large and it becomes difficult to make the permeation flow rate constant, and if it is 1% or less, the flow rate of the filtrate becomes too small, and there is a concern that the water quality will deteriorate due to the propagation of microorganisms.

According to the method of operating the flat sheet membrane filtration apparatus of the present invention, the filtration resistance can be stabilized and the filtrate can be supplied to the use point at a stable and substantially constant flow rate. This is clear from the test results of the following examples and comparative examples.

The flat sheet membrane filtration apparatus used is as follows. That is, in the flat filtration membrane cell alone, the filtration flow path holding member is a polypropylene net having a thickness of 0.12 mm, the flat membrane has a molecular weight cutoff of 750,000, and the pure water permeation water amount is 45 m ³ / (m ² · day). A polysulfone membrane having a width of 120 cm and a length of 60 cm was used, the number of stacked cells was 6, and the undiluted solution flow path gap between the cells was 10 mm. The effective membrane area was 6 m ² .

Using this flat membrane type filtration device, the initial filtration flow rate was 1.6% (0.7 m) of the pure water permeation amount of 45 m ³ / (m ² · day).
³ / (m ² · day)), the filtration side decompression degree of the flat sheet membrane filtration device is set to filter river water with a turbidity of 10 and
Air scrubbing was performed at an air flow rate of 1.8 Nm ³ / h for 1 minute every hour, and the degree of vacuum was adjusted so as to maintain the initial filtration flow rate. The reduced pressure state is the curve I in FIG.
It was as shown in.

On the other hand, in order to set the initial filtration flow rate to 6.7% of the pure water permeate flow rate of 45 m ³ / (m ² · day) (3.0 m ³ / (m ² · day)), the flat membrane type The degree of pressure reduction on the filtration side of the filtration device is set, and in the same manner as above, the river water is subjected to a filtration treatment and air scrubbing cleaning, and the degree of pressure reduction is adjusted so that the initial filtration flow rate is maintained. It was as shown in the curve II of FIG.

As is clear from the comparison between the curves I and II in FIG. 3, according to the method for operating the flat sheet membrane filtration apparatus of the present invention, it is possible to sufficiently suppress the increase in filtration resistance over time, and it is possible to obtain sufficient results. The filtrate can be supplied under a stable flow rate.

In the above-mentioned embodiment of the present invention, the flat filtration membrane cells are used by stacking them, but a plurality of flat filtration membrane cells are used in a liquid tank to be treated with appropriate supporting means. It is also possible to stand upright and maintain a predetermined stock solution flow path gap between the flat filtration membrane cells. Further, although the permeation side of the flat filtration membrane cell is depressurized to generate the transmembrane pressure difference, it is also possible to pressurize the stock solution side of the flat filtration membrane cell to generate the transmembrane pressure difference.

[0022]

EFFECTS OF THE INVENTION According to the method for operating a flat sheet membrane filtration apparatus of the present invention, it is possible to sufficiently mitigate the increase in filtration resistance over time, and to stabilize the filtration resistance, and to suppress fluctuations in the flow rate of the filtrate over time. Yes, reduce air scrubbing air flow, or
Even if the frequency is reduced, it is possible to sufficiently reduce the decrease in the filtrate flow rate over time, to stably maintain the physical strength of the flat sheet membrane, and to extend the life of the flat sheet membrane filtration device, while supplying a stable flow rate of the filtrate. Can be guaranteed.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a flat sheet membrane filtration device used in the present invention.

2 (a) is an explanatory view showing a laminated structure of flat filtration membrane cells in the flat filtration device of FIG. 1, and FIG. 2 (b) is an explanatory view showing flat filtration membrane cells. Is.

FIG. 3 is a chart showing permeation side pressure states of the present invention and a conventional example.

[Explanation of symbols]

 A Layered structure of flat filtration membrane cell 42 Undiluted solution supply pipe 44 Permeate extraction pipe 45 Vacuum pump 48 Air diffuser 49 Blower

Claims (1)

[Claims] 1. A method for filtering an undiluted solution by using a flat-type filtration membrane cell having a filtration fluid channel inside a membrane, wherein an operating filtration fluid flow rate is set under a transmembrane pressure difference of 1 kg / cm ² . A method for operating a flat sheet membrane filtration device, characterized in that the filtration flow rate of pure water is set to a constant value within 1% to 5%.