JPH07132213A - Membrane filtration method and membrane filter - Google Patents

Abstract

PURPOSE:To cope with variations in the inflow of raw water without requring complicated control and expensive equipment in a membrane filtration method obtained by differences in water level by obtaining the fixed flow rate of treated water with the water level in a treating tank baing changed corresponding to a change in the filtration resistance of a membrane. CONSTITUTION:An MF membrane module 3 is installed in the bottom part of a filter tank 1, and a raw water storing space 12 occupies the upper part of the filter tank. The filter tank 1 whose upper part is opened is provided with a raw water pipe 6 and an in-tank water level detecting electrode 9, and an outflow pipe 7 communicating with a treated water tank 2 through the MF membrane 3 below in the upper and lower parts respectively. In the raw water pipe 6, a raw water valve 4 for controlling the inflow of raw water and a raw water flowmeter 5 are provided, and in the outflow pipe 7, an outflow valve 8 for turning on an off the outflow of treated water is provided. In this filtration method, only by opening the raw water valve 4, driving force for passing raw water through the MF membrane 3 is caused by difference in water level between the filter tank 1 and the treated water tank 2. The water level is changed from 10 to 11 with the in filtration resistance to always assure a pressure corresponding to the filtration resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtration treatment technology applied to water treatment such as tap water, irrigation water, waste water or river purification.
Particularly, it relates to a microfiltration membrane filtration treatment technology at a constant flow rate.

[0002]

2. Description of the Related Art Conventionally, an external pressure type microfiltration membrane (MF
In order to perform a constant flow rate process, that is, a process in which the amount of treated water to be filtered is always a fixed amount, in a membrane filtration device in which a membrane is immersed, a device is attached to the suction side, for example, a suction pump. In that case, control based on the number of revolutions or valve opening, installation of a constant flow valve, or suction method using a positive displacement pump is adopted. That is, as shown in FIGS. 3 to 6 below, an external pressure type microfiltration membrane 3 is placed in an open type filtration tank 1, raw water is supplied to the filtration tank 1 from a raw water pipe 6, and the raw water is filtered by the filtration membrane 3. In the membrane filtration device for filtering and flowing out from the treated water outflow pipe 7, for example, i) a constant flow rate treatment using a suction method with a capacity pump, as shown in FIG. 3, a capacity pump 13 communicating with the inside of the filtration membrane 3 is used. However, the capacity pump is more expensive than a normal pump, and the required power is large. Further, ii) the constant flow rate processing using the rotation speed control of the suction pump is performed by installing a flow meter 15 in the treated water pipe and controlling the rotation rate of the processing pump 14 to a constant flow rate, as shown in FIG. Furthermore, iii) the processing of constant flow rate using the control by the opening degree of the valve is performed by the flow meter 15 in the treated water pipe as shown in FIG.
Is installed and the opening of the control valve 16 is controlled so that the flow rate is constant. Still further, iv) the constant flow rate processing by the method of installing the constant flow rate valve utilizes the water level difference between the filtration tank 1 and the treated water tank 2 as shown in FIG. Set up.

In the above-mentioned conventional method, in order to carry out a constant flow rate processing, complicated control is required and expensive equipment must be installed. The processing of the constant flow rate by the method of installing the constant flow rate valve 18 in the above iv) does not require complicated control.
However, since the constant flow valve is used, a pressure loss occurs due to the operation of the constant flow valve, and the water level difference cannot be effectively used. That is, when the water level in the tank drops and the water level difference becomes smaller than a certain value, the treated water cannot be obtained due to the pressure loss due to the constant flow valve, and the treatment must be stopped. In this way, in the processing of constant flow rate by the method of installing the constant flow rate valve, when there is some fluctuation in the raw water inflow rate, the processing flow rate is fixed by installing the constant flow rate valve, so the filtration tank (membrane dipping tank) Or it is also called a treatment tank)
The treatment is stopped or a flow rate always larger than the treatment flow rate is caused to flow in, so that the raw water in the membrane dipping tank overflows.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is a suction method utilizing a water level difference and a membrane filtration method which maximizes the water level difference. Moreover, the subject of this invention is a membrane filtration apparatus which can respond to the fluctuation | variation of the raw water inflow rate, without requiring the above complicated control and expensive equipment.

[0005]

The present invention is to adjust the external pressure in a natural equilibrium manner corresponding to the increase in the membrane filtration resistance, and the above-mentioned subject is achieved by the membrane filtration method of the present invention. That is, (1) in the membrane filtration method in which the pressure required for permeation of the external pressure type microfiltration membrane module is obtained by the water level difference between the raw water level in the treatment tank and the outflow water level of the treated water, it corresponds to the change in the filtration resistance of the membrane. The membrane filtration method is characterized in that a constant flow rate treated water is obtained by changing the water level in the treatment tank. (2) In the membrane filtration method in which the pressure required for permeation of the external pressure type microfiltration membrane module is obtained by the water level difference, the change in the filtration resistance of the membrane is measured and adjusted by the water level in the treatment tank. ) The membrane filtration method described in. And

The above natural equilibrium type membrane filtration method is realized by the following filtration device. That is, (3) an external pressure type microfiltration membrane module is arranged in the treatment tank, and a treated water outflow pipe for letting out treated water to a position lower than the water level in the treatment tank is provided, and the filtration membrane module is provided at the bottom of the treatment tank. A membrane filtration device provided with a raw water level measuring and inflow adjusting means while holding a water storage space equivalent to the differential pressure necessary for filtration above the filtration membrane module. Alternatively, (4) an external pressure type microfiltration membrane module is arranged in the treatment tank, and a treated pipe is connected to the filtration membrane module and a treated water tank arranged at a position lower than the water level of the treatment tank and treated water from the treated water tank. In a membrane filtration device equipped with a treated water outflow pipe, the filtration membrane module is arranged at the bottom of the treatment tank, a flow rate adjusting means is arranged in a raw water supply pipe, and the filtration membrane module is provided above the filtration membrane module. This is a membrane filtration device that holds a water storage space corresponding to a necessary differential pressure and is provided with a raw water level measuring and inflow adjusting means.

In the membrane filtration method and the membrane filtration apparatus of the present invention, for example, if the raw water level measuring means is placed in the treatment tank and the water level of the raw water is monitored, the change in filtration resistance of the membrane can be found. Even if the filtration resistance of the membrane increases and the water level of the raw water tends to rise, it is normally stabilized at the naturally raised water level of the raw water, but in some cases it may be adjusted by a raw water inflow adjusting means or the like.

(5) In the membrane filtration device of the present invention described in (4) above, the treated water tank is a membrane filtration device provided at a position for holding the water storage level above the upper end of the filtration membrane module. Will be more stable. What is important in the present invention is that the water storage level of the treatment tank is a water level capable of holding a considerable water storage space at the time when the filtration resistance of the filtration membrane does not increase so much, and the water storage level increases even if the filtration resistance increases. Therefore, it is possible to secure a certain outflow of treated water. As a result, it is not necessary to wash or replace the membrane for a long period of time. Further, (6) the membrane filtration device according to (3) or (4), in which a siphon device is formed by connecting at least a vacuum pump and a vacuum pipe to the communication pipe. This is a means for always keeping the inside of the communication pipe full of water.

In the present invention, it is important that the treated water outlet pipe communicating with the filtration membrane module and the communication pipe connecting the filtration membrane module and the treated water tank are always filled with treated water. It is also important that this communication pipe does not have a pump, a valve, or anything that can resist the outflow of treated water. If the treated water outflow pipe and the communication pipe are always filled with treated water, a water level difference that naturally corresponds to the filtration resistance is created (the water level of the raw water in the treatment tank is naturally determined), and membrane filtration is performed. is there. Further, if the treated water outlet from the treated water tank is the position of the present invention, the position of the communication pipe in the middle of the treated water outlet may be above the water level in the treated tank. It has the effect that it is easy to respond to fluctuations in the internal water level.

Even if air bubbles are present in the communication pipe, the outflow of the treated water will not be cut off if the communication pipe has a monotonically downward slope from the outflow pipe of the filtration membrane module to the water level of the treated water tank.
Further, as described above, the treated water flows out even if there is a valve such as a constant flow valve. However, in such a situation, resistance was generated in the communication pipe, which disrupted the steady outflow and disrupted the water balance in the membrane immersion tank, such as when the raw water inflow rate fluctuated slightly. become.

In the present invention, the treatment tank in which the filtration membrane module is immersed and the treated water tank of the treated water are installed separately, and there is a part where the communication pipe connected between them rises once, and the treatment pipe above the water level of the treatment tank. It may be, but it doesn't matter.
In such a case, as described in (6) above, it is desirable to provide equipment that can form a siphon device by connecting a vacuum pump and a vacuum pipe to the communication pipe.

In order to understand the present invention, description will be added below with reference to FIG. However, the embodiment of the present invention is not limited to this description.

EXAMPLES In the present invention, an ON-OFF valve may be installed on the treated water side, but no equipment is installed. It is possible to install a simple flow meter on the raw water side and change the flow rate with a manual valve. In the present invention, the differential pressure required for membrane filtration appears as the water level in the immersion tank. When the filtration resistance is low at the initial stage of filtration, the water level in the tank is also low (LWL in FIG. 1). When the filtration resistance increases by continuing the filtration process, the water level in the tank rises (HWL in FIG. 1). Since there is no constant flow rate valve that causes a new differential pressure in the outflow pipe, the difference in water level between the filtration tank and the treated water tank is effectively used for filtration as the differential pressure between the membranes.

Further, in the present invention, the rise in transmembrane pressure can be detected at the water level without installing a pressure gauge. further,
Even if the flow rate of raw water slightly fluctuates, the water level of the dipping tank (treatment tank) fluctuates if the difference between the membrane immersion tank and the treated water tank is less than the maximum water level, but the raw water quantity and the treated water quantity are the same, and there is a natural fluctuation Absorb. When starting the treatment, it is only necessary to open the valves on the raw water side and the outflow side and allow the raw water to flow in. The opposite is true for a stop. Further, as shown in FIG. 2, if the water level of the treated water tank is set above the membrane, ON-O on the inflow side
The FF valve is also unnecessary. When the raw water valve is opened and raw water is allowed to flow in, the treatment is started from the water level above the membrane, and the water level in the tank is adjusted according to the filtration resistance of the filtration membrane. If you close the raw water valve,
The water level in the tank gradually decreases and stops at the level of the treated water tank (upper part of the membrane). From this, it is understood that the membrane is not exposed to the atmosphere, and the treatment can be performed only by turning on and off the raw water valve.

The outline of the apparatus of the present invention is as shown in FIG. In FIG. 1, the MF membrane module 3 is provided at the bottom of the filtration tank 1 and has a raw water storage space 12 at the top thereof. In FIG. 1, the raw water storage space 12 is a space having a uniform cross-sectional area from the bottom to the upper portion, but the storage space 12 only needs to secure a water level above. Therefore, the area does not have to be the same as the area where the membrane module 3 is installed. For example, it may have a chimney shape with an extremely small area. A raw water pipe 6 and an in-tank water level detection electrode 9 are provided in the upper part of the filtration tank 1 having an open upper part, and an outflow pipe 7 communicating with the treated water tank 2 via the MF membrane 3 is provided in the lower part. The raw water pipe 6 is provided with a raw water valve 4 and a raw water flow meter 5 for controlling the raw water inflow, and the outflow pipe 7 is provided with an outflow valve 8 for turning on / off the treated water outflow. However, neither the suction means of the treated water, that is, any artificial device for generating the driving force of the MF membrane 3 portion nor the flow rate adjusting means is arranged. As described above, the filtration method of the present invention only opens the raw water valve 4, and the raw water is MF.
The driving force passing through the membrane 3 is generated by the difference in water level between the filtration tank 1 and the treatment tank 2. As the filtration resistance increases, the water level changes from 10 to 11, and it is possible to always obtain a pressure commensurate with the filtration resistance. The outflow rate can be adjusted by the raw water valve 4.

[0015]

EFFECTS OF THE INVENTION By the membrane filtration method and apparatus of the present invention, (1) a constant flow of treated water can be obtained without using complicated control or expensive equipment, and the treated water can be used systematically. Can be measured. (2) Since no complicated control or expensive equipment is used, the equipment cost can be reduced. In addition, maintenance is easy. (3) Maintenance is also facilitated by the fact that it is a natural equilibrium type filtration. (4) In the filtration device of the present invention, by making the maximum use of the water level difference, it is not necessary to wash or replace the membrane for a long period of time. (5) Since the filter device of the present invention can sufficiently store the raw water in the treatment tank, it can withstand the fluctuation of the raw water inflow amount.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a filtration device of the present invention having a water level detection electrode in a treatment tank.

FIG. 2 is an explanatory diagram showing an example of a filtration device of the present invention that does not require water level detection.

FIG. 3 is a schematic diagram showing an example of a conventional quantitative filtration device equipped with a capacity pump.

FIG. 4 is a schematic diagram showing an example of a conventional quantitative filtration device of a type in which a pump is controlled by a flow meter.

FIG. 5 is a schematic diagram showing an example of a conventional quantitative filtration device of a type in which a valve is controlled by a flow meter.

FIG. 6 is a schematic diagram showing an example of a conventional quantitative filtration device equipped with a constant flow valve.

[Explanation of symbols]

 1 Filtration Tank 2 Treated Water Tank 3 MF Membrane Module 4 Raw Water Valve 5 Raw Water Flow Meter 6 Raw Water Pipe 7 Raw Water Pipe 7 Treated Water Outflow Pipe 8 Outflow Valve 9 Tank Water Level Detection Electrode 10 Low Water Level 11 Storage Space 13 Capacity Pump 14 Treatment Pump 15 Flow meter 16 Control valve 17 Pump 18 Metering valve

Claims (4)

[Claims] 1. A membrane filtration method in which the pressure required for permeation of an external pressure type microfiltration membrane module is obtained by the difference in water level between the raw water level in the treatment tank and the outflow water level of the treated water, which corresponds to a change in filtration resistance of the membrane. The membrane filtration method is characterized in that a constant flow rate treated water is obtained by changing the water level in the treatment tank. 2. In a membrane filtration method for obtaining a pressure required for permeation of the external pressure type microfiltration membrane module by a water level difference, a change in filtration resistance of the membrane is measured and adjusted by a water level in a treatment tank. Item 1. The natural equilibrium type membrane filtration method according to Item 1. 3. An external pressure type microfiltration membrane module is arranged in the treatment tank, and a treated water outflow pipe is provided at a position lower than the water level in the treatment tank, and the filtration membrane module is provided at the bottom of the treatment tank. And a flow rate adjusting means is arranged in the raw water supply pipe, a storage space equivalent to the differential pressure necessary for filtration is held above the filtration membrane module, and raw water level measuring and inflow adjusting means are provided. Membrane filtration device. 4. An external pressure type microfiltration membrane module is disposed in the treatment tank, and a communication pipe for communicating the filtration membrane module and the treatment water tank disposed at a position lower than the water level of the treatment tank and the treated water from the treatment water tank. In a membrane filtration device having a treated water outflow pipe for outflowing, the filtration membrane module is arranged at the bottom of the treatment tank, and a flow rate adjusting means is arranged at the raw water supply pipe.
A membrane filtration device, characterized in that a water storage space corresponding to a differential pressure required for filtration is held above the filtration membrane module, and raw water level measurement and inflow adjustment means are provided.