JPH04247226A - Membrane filtration system having automatic self-cleaning function - Google Patents

Abstract

PURPOSE:To prevent the variation in the amt. of filtered water as the quality of raw water varies momentarily and to obtain the stabilized amt. of filtered water. CONSTITUTION:This system is provided with a means 5 for detecting the variation of the quality of raw water and a means 6 for detecting the amt. of the filtered water obtained by passing the raw water through a membrane module 10. Since the detected amt. of filtered water is related to the variation in the quality of raw water, the amt. of filtered water and the quality of raw water are detected and confirmed, a backwashing pump 4 is operated when the amt. of filtered water decreases to backwash the module 10, and the amt. of filtered water is stabilized.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to the production of sterile water used for dissolving raw materials and cleaning pipes used in water supply facilities for the purpose of producing drinking water, pharmaceuticals, fermentation factories, food factories, etc. The present invention relates to a membrane filtration method suitable for equipment, sewage treatment water recycling equipment, factory process water closure, reuse equipment, etc.

0002

[Prior Art] In recent years, contamination and depletion of water resources have become a problem, and there is a system for completely removing contaminants from water and aqueous solutions (hereinafter referred to as raw water) to produce drinking water and sterile water. The filtration and reuse system for raw water is attracting attention. Increasingly, reverse osmosis membranes, ultrafiltration membranes, or microfiltration membranes (all of these are simply referred to as membranes hereinafter) are used in this type of system.

[0003] Conventionally, this type of membrane filtration equipment supplies fluid parallel to the membrane surface in order to prevent the amount of filtrate (hereinafter referred to as filtrate amount) from decreasing due to the adhesion of a gel layer or cake of the filtered material to the membrane surface. In many cases, a cross-flow method is used to flow through the membrane and filter it, and in order to further increase the membrane area, a membrane module (hereinafter referred to as "membrane module") is an integrated membrane module in which a large number of hollow fibers with fine holes on the surface are inserted into a resin or metal tube. In most cases, modules are used. There are many types of hollow fibers such as organic membranes such as polyacrylonitrile, polysulfone, and cellulose, and inorganic membranes such as ceramics.

[0004] In addition, in this type of membrane system, back pressure washing (hereinafter referred to as backwashing) described below is incorporated into the system in order to periodically remove deposits on the membrane surface and obtain a stable amount of filtration. There are many cases.

[0005] There are two types of filtration using hollow fiber modules: an internal pressure type in which the filtrate is taken out to the outside while the stock solution passes through the inner surface of the hollow fiber, and an external pressure type in which the filtrate is taken out to the inside while the stock solution passes through the outer surface. There are several types of backwashing, but backwashing is the process of supplying filtrate or pre-prepared clean water at a certain pressure for a certain period of time from the side opposite to the side through which the stock solution passes, thereby cleaning the membrane surface by physical force. This method washes away the deposits.

[0006] When there is little fluctuation in the quality of raw water, the stability of the filtrate can be obtained by alternately switching between filtration and backwashing using a timer, etc. However, when there is a large fluctuation in the quality of raw water, the amount of filtrate decreases. The only way to deal with this problem was to check the situation and then change the timer settings one by one, which was extremely incomplete as the membrane had already become clogged and the filtration rate could not be recovered, and monitoring and management required human labor.

[0007]

[Problems to be Solved by the Invention] The present invention solves the above-mentioned problems of the prior art regarding a filtration system of a hollow fiber type membrane filtration system. The object of the present invention is to provide a membrane system that can operate continuously for a long period of time and can always obtain a stable amount of filtration.

[0008]

[Means to solve the problem] The factors that cause fluctuations in the quality of raw water are: ■ Increase in COD (chemical oxygen demand) and BOD (biological oxygen demand) components; ■ SS (suspended solids), TDS (
Increase in evaporation residue) components, ■ Increase in microorganisms, ■ MBAS
This is due to an increase in (surfactant) components, ■ Fluctuations in chromaticity, ■ Increases in odor, ■ Increases in oil content, etc. The present invention detects changes in the quality of raw water as described above, and changes the detected contents. The feature of this system is that it automatically changes the backwash setting value when it is found to be the cause of a decrease in filtration rate, prevents membrane clogging, and continuously obtains a stable filtration rate.

[0009]

[Operation] The membrane filtration method according to the present invention includes a water quality detection section for raw water at the supply section to the raw water tank or the raw water inflow section near the membrane module inlet, detects the changing quality of the raw water, and allows the water to pass through the membrane module. The amount of filtration is detected and confirmed, and if the amount of filtration tends to decrease within a predetermined period of time, the backwashing conditions for the membrane are changed to automatically adjust the amount of filtration to a preset amount.

0010

[Embodiment] An embodiment of the present invention will be explained based on the drawings. In the figure, 1 is a raw water tank, and raw water in the raw water tank 1 is supplied into the membrane module 10 by a supply/circulation pump 3 installed in a supply pipe A that connects the raw water tank 1 and the membrane module 10. . 5 is a turbidity sensor disposed in the supply pipe A, and 7 is a module inlet automatic valve also disposed in the supply pipe A. The raw water supplied to the membrane module 10 by the supply/circulation pump 3 described above is
Contaminants 17 in the raw water are passed through the membrane module 10.
, 17, . Reference numerals 8 and 6 denote flow rate sensors including an automatic filtrate outlet valve, an electromagnetic flowmeter, etc., which are disposed in the filtrate supply pipe C from the membrane module 10 to the filtrate tank 2.

D is the membrane module 1 of the supply pipe C described above.
It is a backwashing pipe branched from near the outlet of 0 and connected to the lower part of the filtration tank 2, and the backwashing pipe D is provided with a backwashing pump 4 and an automatic backwashing valve 9. ing. Also, 11
12 is a level meter that detects the level in the raw water tank 1, and 12 is a turbidity sensor 5 installed in the raw water supply pipe A that measures COD (chemical oxygen demand) and BOD (biochemical oxygen demand) in the raw water. amount), SS (suspended solids), TDS (vapor residue)
, MBAS (surfactant), etc.

The above-mentioned supply and circulation pump 3 may be installed separately into two units, a supply pump and a circulation pump, or the membrane-filtered raw water is partially blown out of the system to reduce the concentration in the raw water tank 1. In some cases, it may be kept constant. Furthermore, Figure 1
E in 13 is the raw water supply pipe to the raw water tank 1.
is an automatic valve installed in the raw water supply pipe D.

[0013] Since this embodiment is configured as described above, its operation will be explained first. First, the initial setting value of the filtration rate, the confirmation time of the flow rate change, the filtration time, the backwash time, and the initial setting of the turbidity. Determine the value and input it into the device. In this example, the flow rate was 500 l/Hr, and the confirmation time was 2Hr.
The filtration time was 30 minutes, the backwash time was 30 seconds, and the initial setting value of turbidity was 5, and operation was started in these conditions.

When the operation is started, the module inlet automatic valve 7 installed in the raw water supply pipe A connecting the raw water tank 1 and the membrane module 10 and the filtrate supply connecting the membrane module 10 and the filtrate tank 2 The automatic filtrate outlet valve 8 disposed in the pipe C is opened, the automatic backwash valve 9 disposed in the backwash pipe D is closed, and the backwash pump 4 is stopped. Raw water supply pipe A
When the circulation pump 3 is operated to supply the raw water in the raw water tank 1 into the membrane module 10, the raw water flows in the direction of arrow 15, and the filtrate filtered in the membrane module 10 flows in the direction of arrow 16. It flows in the direction of filtrate and is supplied from the membrane module 10 into the filtrate tank 2 via the filtrate supply pipe C. At this time, current control is performed on the above-mentioned supply and circulation pump 3 so that the flow rate detected by the flow rate sensor 6 installed in the filtrate supply pipe C maintains the initial setting value, and the rotation speed is arbitrarily changed. I am made to do so.

When the initial filtration time of 30 minutes has elapsed, the module inlet automatic valve 7 disposed in the raw water supply pipe A and the filtration automatic valve 8 disposed in the filtrate supply pipe C are closed, and the said pipe is closed. Open the automatic backwash valve 9 installed in the backwash pipe D branched from the line C and connected to the bottom of the filtration tank 2, and then open the supply and circulation pump 3 installed in the raw water supply pipe A. may be running or stopped. When the backwash pump 4 of the backwash pipe D is operated for an initial set backwash time of 30 seconds, the contaminants 17, 17, . . . adhering to the inside of the membrane are removed and cleaning is performed. In this way, by repeating the filtration and backwashing operations, the filtrate is stabilized. The amount of water in the raw water tank 1 is detected by a level meter 11, and the automatic valve 13 of the supply pipe E is opened and closed to maintain a constant amount of raw water in the tank 1.

[0016] If the raw water turbidity value (output signal current from the sensor) does not change and the filtration rate does not decrease within the confirmation time, the raw water circulation time will increase and the frequency of backwashing will decrease. becomes. In the example, if there is no change in the drainage amount for 2 hours after operation, the circulation time is extended by 5 minutes, and the backwash time is fixed at 30 seconds.

[0017] Furthermore, when the values of BOD, COD, and turbidity in the raw water increase, the turbidity sensor 5 detects the increase, and the value of the filtration amount is confirmed by the sensor 6, and the filtration amount tends to decrease within a predetermined time. If so, shorten the circulation time and increase the backwash frequency or backwash time. In the example,
If the turbidity increases and the drainage rate decreases within 2 hours after operation, the circulation time shall be reduced by 5 minutes, and then the confirmation time 2
A control system was constructed to further shorten the circulation time by 5 minutes if the drainage rate continued to decrease over time. In the example, the turbidity and flow rate were checked every two hours, and the circulation time was varied so that a constant amount of drainage could be obtained.

[0018] Furthermore, when the filtration rate decreases due to factors other than turbidity, such as temperature, the flow rate sensor 6 increases or decreases the rotational speed of the supply and circulation pump 3, and the control system controls the filtration rate to maintain the initial set value. was constructed so that it could be switched arbitrarily.

In the examples, in order to change the turbidity of raw water, tests were conducted using kaolin as the turbidity and changing the turbidity from 1 to 10. As a result, the filtration time is 20
The time was changed arbitrarily within the range of 120 minutes to 120 minutes, and the drainage amount could always satisfy the initial setting value of 500 l/Hr. Further, the turbidity sensor used in this example was a phototube type sensor with a 4 to 20 mA output terminal. In addition, the turbidity sensor 5
may be located at the supply part of the raw water tank 1 or anywhere within the circulation system (including the raw water tank). In addition to the BOD and COD values, the device of this embodiment also has the S
All sensors that can detect raw water components such as S, microorganisms, TDS, MBAS, turbidity, color, and odor can be used.

[0020]

Effects of the Invention The membrane filtration method according to the present invention detects raw water components that change every moment, and also detects the amount of filtrate obtained by passing the raw water through a membrane module, and detects an increase or decrease in the detected amount of filtrate. Since this is related to the change in the raw water components mentioned above, when the filtrate rate decreases, the membrane module can be backwashed to automatically prevent the decrease in filtrate due to membrane clogging without special monitoring or management. It is possible, and the effects are remarkable.

[Brief explanation of the drawing]

[Figure 1] Flow diagram showing an example of implementation of membrane filtration method

[Figure 2
】Explanatory diagram of filtration mechanism

[Figure 3] Illustration of the backwash mechanism

[Explanation of symbols]

1 Raw water tank 2 Filtrate tank 3 Supply and circulation pump 4 Backwash pump 5 Turbidity sensor 6 Flow rate sensor 7 Module inlet automatic valve 8 Automatic filtration outlet valve 9 Automatic backwash valve 10 Membrane module

Claims (1)

[Claims] 1. A detection means for detecting a change in the quality of raw water, and a means for detecting the amount of filtrate obtained by passing the raw water through a membrane module, A membrane filtration system having an automatic self-cleaning function, characterized in that the membrane of the membrane module is automatically washed according to the amount of water to obtain a stable amount of water filtration.