JPH0975938A - Membrane separation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain constant filtering performance regardless of properties of a liquid in a membrane separation device equipped with a draining means to drain sludge from a treating tank having a membrane module and an aerating means, by measuring the viscosity coefft. of the liquid in the tank and controlling the draining means for sludge based on the measured value. SOLUTION: This membrane separation device has a membrane module 2 immersed in an aeration tank 1 which is aerated by an aerating pipe 4 connected to a blower 3 so that the feed water introduced into the tank 1 through a pipe 5 is treated with aerobic microorganisms. In this method, a measuring means 11, 12 for the viscosity coefft. (or a physical index which has correlation with the viscosity coefft.) is disposed in the inside and outside of the tank l. According to the measured value, the aeration amt. by the blower 3 and opening and closing of a valve 9A attached to a sludge draining tube 9 are controlled by a controlling unit 13. For example, if the viscosity coefft. increases over a specified value, the draining amt. of sludge through the pipe 9 is increased to decrease the viscosity coefft., while the aeration amt. is increased to increase an air-lifted circulating flow.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a membrane separation device,
In particular, the present invention relates to a membrane separation device in which a membrane module is immersed and installed in a treated water tank, and efficient cross-flow filtration is performed by an air lift circulation flow generated by aeration from the lower portion of the membrane module.

[0002]

2. Description of the Related Art Conventionally, there has been proposed a membrane separation device in which a membrane module is immersed in an aeration tank and efficiently filtered by an air lift circulating flow generated by aeration from below the membrane module.

FIG. 2 shows such a membrane separation device, in which a membrane module 2 is immersed in an aeration tank 1 and aerated from below the membrane module 2 with a blower 3 and an air diffusing pipe 4. Raw water is introduced into the aeration tank 1 through the pipe 5, and aerobically treated in the tank. The biological treatment liquid is a suction pump 6
Membrane filtration is performed with a high permeation flux by the intermittent suction by and the rising liquid of the air lift circulation flow due to aeration, and the permeated water is discharged from the system through the pipe 7. Reference numeral 8 is a straightening plate for generating a good air lift circulation flow. Reference numeral 9 is a sludge drawing pipe, and the sludge in the aeration tank 1 is withdrawn from the pipe 9 intermittently or continuously.

Further, in the membrane separation apparatus as shown in FIG. 2, there has been proposed a method of preventing clogging of the membrane by adjusting suction pressure and aeration amount based on the organic matter concentration of the liquid to be treated.

Further, in order to form a good air lift circulation flow by aeration, as shown in FIG. 3, a treated water tank is a raw water tank 1A into which raw water is introduced, and a separation membrane tank 1B in which a membrane module 2 is installed. Divide into two and connect both tanks 1A and 1B to the communication pipe 1
Those that communicate with 0A and 10B are also proposed. In addition,
In FIG. 3, members having the same functions as those shown in FIG. 2 are designated by the same reference numerals.

Such a membrane separator is used as a membrane separator for biologically treating organic wastewater to perform solid-liquid separation of activated sludge, or as a coagulation treatment of organic or inorganic wastewater to agglomerate colloidal components. It is used as a membrane separator for solid-liquid separation of treated coagulated sludge.

In the submerged membrane separation apparatus utilizing the air lift circulation flow due to the aeration, the filtration pressure is obtained by the head difference or suction pressure, so that high pressure operation unlike the pressure circulation type membrane separation apparatus is not required. Therefore, efficient membrane filtration can be performed at a low pressure without consolidating the membrane exclusion material deposited on the membrane surface. Since cross-flow filtration is performed with an air lift circulation flow, a large amount of water can be circulated with a small amount of energy. Therefore, even when the membrane modules are arranged in multiple stages and treated, efficient treatment can be performed without causing a reduction in filtration efficiency of the membrane modules at the end portion. Such an excellent effect is achieved.

[0008]

In the pressure circulation type membrane separation device in which the liquid to be treated is forcibly fed under pressure by the circulation pump, the liquid properties such as the viscosity coefficient of the liquid to be treated are selected by selecting an appropriate pump. The filtration performance can be maintained with almost no effect, but in the air-lift circulation type membrane separation device, the apparent density difference between the liquid inside and outside the membrane module is used as the driving force for liquid circulation, so It is easily affected by the properties, particularly the viscosity coefficient, and when the viscosity coefficient increases, the fluidity of the liquid decreases, so the airlift circulation flow decreases. Further, the entrainment amount of bubbles in the downflow portion of the airlift circulation flow also increases with an increase in the viscosity coefficient, so that the density difference inside and outside the membrane module decreases, and the airlift circulation flow further decreases.

As described above, since the air lift circulation flow decreases due to the increase of the viscosity coefficient, the force for sweeping the film surface deposit in the cross flow filtration also decreases, and the film surface deposit increases due to the increase of the film surface deposit. There is a problem that filtration resistance increases and filtration performance decreases.

In the conventional air lift circulation type membrane separation device, the decrease in the air lift circulation flow due to the increase in the viscosity coefficient of the liquid to be treated and the deterioration in the filtration performance due to the decrease
It was an important issue to be solved.

By adopting a method of adjusting the suction pressure and aeration based on the organic matter concentration of the liquid to be treated, although some effects can be obtained, a treatment sufficiently corresponding to the increase of the viscosity coefficient is applied, It is difficult to reliably maintain the filtration performance for a long period of time.

The present invention solves the above-mentioned problems of the prior art, and maintains a constant filtration performance even when the properties of the liquid to be treated fluctuate, and an air lift circulation type membrane capable of stable and efficient treatment. An object is to provide a separation device.

[0013]

The membrane separation device of the present invention comprises:
A treated water tank into which a liquid to be treated is introduced, a membrane module immersed in the treated water tank, an aeration means provided at a lower portion of the membrane module, and a treated water take-out for extracting permeated water of the membrane module as treated water. Means, in a membrane separation device comprising a sludge drawing means for drawing sludge from the inside of the treated water tank, the viscosity coefficient of the liquid in the tank or a physical index that correlates with the viscosity coefficient is measured, and based on this measured value, the sludge The present invention is characterized in that a control means for controlling the sludge withdrawal amount of the withdrawal means is provided.

The inventors of the present invention have earnestly studied the change of the viscosity coefficient of the liquid to be treated in the air lift circulation type membrane separator, and have found that the following two items are dominant.

Change in Concentration of Suspended Component Change in Concentration of Dissolved Organic Component Among these, the change in concentration of the suspended component is caused by an imbalance between the raw water concentration and the sludge withdrawal amount. On the other hand, the change in the concentration of the dissolved organic component caused by the change in the properties of the raw water and the change in the concentration of the suspended component increased the viscosity coefficient and the filtration resistance of the membrane. This may be due to the fact that the improvement of the water content prevents the permeation of the dissolved organic component to a high degree and the dissolved organic component is concentrated.

From the above, it can be seen that when the viscosity coefficient increases, it can be recovered (reduced) by increasing the sludge withdrawal amount to reduce the concentration of suspended components in the tank.

That is, the viscosity coefficient of the liquid to be treated and the amount of sludge drawn out have a certain relationship in the liquid to be treated, and the viscosity coefficient can be reduced by increasing the amount of drawn sludge.

By increasing the sludge removal amount in this way, the viscosity coefficient can be reduced and the deterioration of the membrane filtration performance can be prevented, but this is not an immediate countermeasure and the sludge removal is not effective. It takes some time for the viscosity coefficient to change by controlling the amount.

Therefore, in the present invention, the control of the aeration amount by the aeration means is performed simultaneously with the control of the sludge withdrawal amount.
Alternatively, it is preferable that the time difference between before and after is provided.

That is, by increasing the aeration amount, the decrease of the air lift circulation flow, which is decreased by the increase of the viscosity coefficient, is compensated for, and the decrease of the cross flow velocity and the decrease of the filtration efficiency are immediately prevented.

In the membrane separation apparatus of the present invention, by controlling the amount of sludge drawn out and further the amount of aeration using the viscosity coefficient as an index, before a deposited layer of contaminants that cannot be easily removed is formed on the membrane surface. It is possible to increase the air lift circulation flow and take good measures, prevent deterioration of the membrane performance, and perform stable and efficient treatment for a long period of time.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the membrane separation apparatus of the present invention. The membrane separation apparatus shown in FIG. 1 is different from the membrane separation apparatus shown in FIG. 2 in that a viscous coefficient (or a physical index that correlates with the viscosity coefficient) measuring means 11 installed inside the tank and a viscous coefficient (or a viscosity outside the tank installed) are used. Physical index that correlates to the coefficient) measuring means 12
Is provided, and the measured values of these measuring means 11 and 12 are input, and based on the input measured values, the control unit 13 that controls the aeration amount of the blower 3 and the opening / closing of the valve 9A provided in the sludge drawing pipe 9 Is provided. The viscosity coefficient measuring means 12 is provided so as to extract sludge from the bottom of the aeration tank 1 through a pipe 15 equipped with a pump 14 to measure the viscosity coefficient, and then return the sludge to the aeration tank 1 through a pipe 16. .

Other configurations of the membrane separation device shown in FIG.
Similar to the membrane separation device shown in FIG. 2, members having the same functions are designated by the same symbols.

In the membrane separation apparatus of this embodiment, the pipe 5
Raw water introduced into the aeration tank 1 from the above is subjected to aerobic biological treatment in the tank, and the biological treatment liquid is subjected to membrane filtration in the membrane module 2,
The permeated water is discharged from the system through the pipe 7. Then, the sludge in the aeration tank 1 is withdrawn from the pipe 9 intermittently or continuously.

In such a membrane filtration process, the viscosity coefficient measuring means 11 measures the viscosity coefficient of the liquid in the aeration tank, and the viscosity coefficient measuring means 12 measures the viscosity coefficient of the sludge extracted from the pipe 15. Is measured, and the control unit 13 controls the amount of aeration by the blower 3 or the amount of sludge drawn out from the pipe 9 based on these measured values.

That is, when the viscosity coefficient exceeds a predetermined value, or when it tends to increase, the amount of sludge drawn out from the pipe 9 is increased to reduce the viscosity coefficient and the aeration amount is increased. To increase the air lift circulation flow.

As a result, the increase in the viscosity coefficient reduces the air lift circulation flow, and further prevents the deposition and growth of deposits that cannot be easily separated on the film surface, and the filtration of the film. High performance can be maintained.

In the present invention, the means for measuring the viscosity coefficient of the liquid to be treated or the physical index correlating with the viscosity coefficient may be either a type installed inside the tank or a type installed outside the tank.
Further, these may be used in combination, but specifically, the following can be used.

Hot-wire anemometer Hot-film anemometer Doppler anemometer Ultrasonic anemometer A torque meter such as a rotational viscometer Among these, when the viscous coefficient measuring means is installed in the tank, it is installed in the rising part of the airlift circulation flow. If it is provided, it may be affected by bubbles and cause a malfunction, so it is preferable to install it in the downward flow portion of the air lift circulation flow. Further, when the viscosity coefficient measuring means is installed outside the tank, it is preferable to measure the liquid at the bottom of the tank continuously or intermittently.

In the membrane separation apparatus shown in FIG. 1, the viscosity coefficient measuring means installed inside the tank and the viscosity coefficient measuring means installed outside the tank are used together, but only one of the viscosity coefficient measuring means is used. But needless to say.

When two types of viscosity coefficient measuring means are used in this way, for example, the sludge withdrawal amount is controlled based on one viscosity coefficient measuring means, and the aeration amount is controlled based on the other viscosity coefficient measuring means. You can Further, one viscosity coefficient measuring means may be used as a control reference during a certain specific period, and another viscosity coefficient measuring means may be used as a control reference during another period. Further, the measured values of both viscosity coefficient measuring means may be substituted into an appropriate arithmetic expression to calculate the most suitable control criterion for the processing condition.

[0033]

As described in detail above, according to the membrane separation apparatus of the present invention, the filtration performance of the membrane is kept high,
Stable and efficient processing can be performed.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a membrane separation device of the present invention.

FIG. 2 is a system diagram showing a conventional membrane separation device.

FIG. 3 is a system diagram showing a conventional membrane separation device.

[Explanation of symbols]

 1 Aeration Tank 2 Membrane Module 3 Blower 4 Diffuser 6 Suction Pump 11, 12 Viscosity Coefficient Measuring Means 13 Control Unit

Claims (1)

[Claims] 1. A treated water tank into which a liquid to be treated is introduced, a membrane module immersed in the treated water tank, an aeration means provided below the membrane module, and permeated water of the membrane module is treated water. In a membrane separation device equipped with a treated water take-out means and a sludge draw-out means for drawing sludge from the inside of the treated water tank, the viscosity coefficient of the liquid inside the tank or a physical index correlated with the viscosity coefficient is measured, and the measured value is Based on the above, the membrane separation device is provided with control means for controlling the sludge withdrawal amount of the sludge withdrawal means.