JP2005246110A - Method for cleaning hollow fiber membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method capable of removing fouling substances deposited to the outer surface of hollow fiber membranes in the vicinity of the binding parts and fouling substances penetrating into fine pores formed in the surface of the membrane and preventing re-deposition of the detached fouling substances after removal. <P>SOLUTION: In a module 1 of external pressure type hollow fiber membranes, two or more hollow fiber membranes 2 comprising an open part 3 at one end and a sealed part 4 at the other end and having many fine pores 5 in the surface are bound together on the opening part 3 side to form a binding part 8, the binding part 8 divides a filtrated water chamber 7 from a raw water chamber 6, and the open part 3 side is positioned to the lower side and the sealing part 4 side is positioned to the upper side. The membranes 2 are cleaned by introducing a liquid and gas simultaneously into the hollow fiber membranes 2 from the open part 3 in the direction from the chamber 7 side to the chamber 6 side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for cleaning an external pressure hollow fiber membrane used in a membrane treatment apparatus. More specifically, the present invention relates to a method for cleaning a hollow fiber membrane, in which a fouling material such as a suspended material adhering to the outer surface of the hollow fiber membrane is cleaned using a liquid and a gas.

  In the process of water treatment by the hollow fiber membrane, fouling substances such as suspended substances contained in the raw water adhere to the outer surface of the hollow fiber membrane or are formed on the surface of the hollow fiber membrane as the filtration time elapses. There has been a problem that the microfluid penetrates into the micropores and the filtration flux of the hollow fiber membrane gradually decreases.

  As a method for recovering this filtration flux, a liquid back-flow cleaning method in which liquid is washed back through the filtration water chamber side opening into the hollow fiber membrane, or a gas back-flow using gas as an alternative to the liquid in the above method A cleaning type physical cleaning method was employed.

  However, with the liquid back-flushing method, the fouling material that has entered the micropores formed on the outer surface of the hollow fiber membrane can be removed, but the fouling material adhering to the outer surface of the hollow fiber membrane can be removed. There was a problem that it was difficult to discharge the fouling substances accumulated between the yarn membranes. In addition, since filtered water is used as the liquid to be used, there is also a problem that the recovery rate decreases due to the use of a large amount of filtered water. In addition, the gas back-flow cleaning method can remove the fouling material that has entered the micropores as well as the liquid back-flow cleaning method, and the hollow fiber membrane can be swung to peel off the fouling material adhering to the outer surface of the hollow fiber membrane. It can also be removed. Furthermore, since no filtered water is used, a reduction in the recovery rate can be prevented, but there is a problem that it is difficult to discharge the fouling material accumulated between the hollow fiber membranes.

  In addition, there are a backflow cleaning method in which the liquid flows back from the filtered water chamber side and a scrubbing cleaning method in which a gas is introduced from the raw water chamber side to swing the hollow fiber membrane and the liquid in the raw water chamber is flowed for cleaning. JP-A-60-19002. This combined method can discharge the fouling material accumulated between the hollow fiber membranes, which is a disadvantage of the liquid backflow cleaning method, when combined with the scrubbing method, but the oscillation of the hollow fiber membrane is insufficient. Removal of the fouling substance adhering to the outer surface of the hollow fiber membrane is not sufficient, and removal in the vicinity of the joint has not been solved. Moreover, the problem that the peeled fouling substance re-adheres to the surface of the hollow fiber membrane has not been studied.

JP-A-60-19002

  The present invention solves such a problem, and the fouling substance adhering to the outer surface of the membrane in the vicinity of the bonding portion of the hollow fiber membrane and the fouling entering the micropore formed on the membrane surface are provided. It is an object of the present invention to provide a cleaning method capable of removing a ring substance and preventing reattachment of a fouling substance peeled for removal.

  In order to achieve the above object, claim 1 of the present invention provides a plurality of hollow fiber membranes on the opening side, each of which has an opening on one end side and a sealing portion on the other end, and a plurality of micropores are formed on the surface. This is an external pressure type hollow fiber membrane module that is combined to form a coupling portion, and is divided into a filtrate water chamber side and a raw water chamber side by the coupling portion, from the opening toward the raw water chamber side from the filtrate water chamber side. The present invention relates to a method for washing a hollow fiber membrane, wherein the hollow fiber membrane is washed by simultaneously introducing a liquid and a gas into the hollow fiber membrane.

  According to a second aspect of the present invention, there is provided the method for cleaning a hollow fiber membrane according to the first aspect of the present invention, wherein the external pressure type hollow fiber membrane module is erected so that the opening side is positioned downward and the sealing portion side is positioned upward. It is concerned.

  The present invention has the following effects.

  That is, in the method for cleaning a hollow fiber membrane of the present invention having the above-described configuration, the liquid and gas are simultaneously introduced into the hollow fiber membrane from the opening toward the raw water chamber side from the filtered water chamber side. It is possible to remove the fouling material that has penetrated into the micropores formed on the surface. Moreover, by introducing the gas, the hollow fiber membrane can be swung from the inside, and the fouling material adhering to the outer surface of the membrane can be peeled off. In particular, the effect of peeling near the joint is great, and the effect of discharging the fouling material accumulated between the hollow fiber membranes is also great. Accordingly, it is possible to prevent the filtration flux from being lowered.

  Further, since the liquid and the gas are introduced at the same time, the amount of filtered water used can be reduced compared to the case of the liquid alone, and the recovery rate of the filtered water can be increased.

  Further, since the hollow fiber membrane is erected so that the coupling portion on the opening side is positioned below and the sealing portion side is positioned above, the liquid and gas that have flowed back from the opening portion are uniformly dispersed by the buoyancy of the gas. Since it passes through the hollow fiber membrane and is discharged from the entire micropores formed on the outer surface of the hollow fiber membrane, the entire hollow fiber membrane can be washed uniformly. Moreover, since the liquid and gas discharged from the micropores float along the surface of the hollow fiber membrane, the fouling substance adhering to the membrane surface has a great peeling effect, and the peeled fouling substance is separated from the gas. Since it is carried upward together with the liquid discharged at the same time, it is possible to prevent re-adhesion and to further prevent the reduction of the filtration flux.

  Preferred embodiments of the present invention will be described below with reference to the drawings. However, the scope of the present invention is not intended to be limited to the contents described in this embodiment unless otherwise specified.

  FIG. 1 is a schematic configuration diagram showing a method for cleaning a hollow fiber membrane module according to an embodiment of the present invention, which is configured as follows.

  This hollow fiber membrane module 1 is for filtering raw water flowing in from a raw water pipe 62 provided with a raw water valve 61 through a hollow fiber membrane 2 and outflowing filtered water from an outflow pipe 12. And a plurality of hollow fiber membranes 2 having a plurality of micropores 5 formed on the surface thereof are joined on the opening 3 side to form a joint 8 and the sealing part 4 side is free. It is constructed so that the coupling portion 8 is located on the lower side and the sealing portion 4 is located on the upper side, and the lower side divided by the coupling portion 8 is the filtered water chamber 7 and the upper side is the raw water chamber 6. ing. In FIG. 1, the number of elements in the hollow fiber membrane module 1 is one, but a plurality of elements may be provided.

  On the raw water chamber 6 side, a raw water pipe 62 having a raw water valve 61 for inflowing raw water, a primary drain pipe 52 having a primary drain valve 51 for discharging washing waste water, and sealing of the hollow fiber membrane 2 are provided. An exhaust pipe 72 having an exhaust valve 71 for discharging liquid and gas when backflow cleaning described later is performed from the space above the stopper 4 is provided. In addition, an outflow pipe 12 is provided on the filtered water chamber 7 side for allowing the filtered water filtered by the hollow fiber membrane 2 to flow out. In the middle of the outflow pipe 12, a water supply pipe 33 having a water backwash valve 35 connected to a backwash water tank 31 via a backwash pump 32 for carrying out liquid backwashing, and for carrying out gas backwashing An air supply pipe 23 having an air backwash valve 21 connected to the compressor 22 and a secondary drain pipe 42 having a secondary drain valve 41 for releasing the pressure of the filtrate water chamber are connected.

  In the raw water filtration step in the apparatus using the hollow fiber membrane module 1 described above, the secondary drain valve 41 and the exhaust valve 71 are first opened and released, and then the secondary drain valve 41 is closed and the raw water valve 61 is opened. After opening and filling the raw water chamber 6 with raw water, the exhaust valve 71 is closed and the filtration valve 11 is opened to start filtration. Filtration is performed by passing raw water through the micropores 5 formed on the outer surface of the hollow fiber membrane 2, and the filtered water flows out into the filtered water chamber 7 through the inside of the hollow fiber membrane. As the filtration time elapses, fouling substances in the raw water adhere to the outer surface of the hollow fiber membrane 2 and the micropores 5 and the filtration flux decreases. At this time, in order to recover the filtration flux, a simultaneous back-flow cleaning process in which the following liquid and gas are simultaneously introduced is performed.

  In the simultaneous backwashing process in which the liquid and the gas are simultaneously introduced, first, the raw water valve 61 is closed to stop the filtration process in order to stop the inflow of the raw water. Next, all valves are closed and the exhaust valve 71 is opened in a state where the compressor has been operated in advance. Thereafter, the water backwash valve 35 is opened and the backwash pump 32 is operated. At the same time, when the air backwash valve 21 is opened, filtered water and air flow from the opening 3 and flow back through the inside of the hollow fiber membrane 2. 5 to the raw water chamber 6 side. The gas and liquid flowing out to the raw water chamber 6 side of the hollow fiber membrane 2 are discharged from the exhaust valve 71. At this time, the pressure and flow rate for the reverse flow of filtered water and air will increase the cleaning effect if the flow rate increases, but the quality of the water to be treated in consideration of the durability and cost of the hollow fiber membrane. And it determines suitably according to the amount of filtrate water. Further, the backwash time is appropriately determined depending on the state of blockage of the membrane. The longer the cleaning time, the greater the cleaning effect, but the energy cost increases and the water recovery rate decreases, so it is usually carried out between 10 seconds and 180 seconds. In addition, the time for performing only one of the cleanings may be provided by changing the cleaning time for air backwashing and water backwashing. In order to enhance the cleaning effect, sodium hypochlorite or acid may be added to the filtered water as a cleaning chemical.

  In order to return to the filtration step after the simultaneous back washing step, the back washing pump 32 is stopped, the water back washing valve 35 is closed, the primary drain valve 51 is opened, and the exhaust valve 71 is closed. Thereby, the washing waste water in the hollow fiber membrane module 1 is discharged. Next, after the primary drain valve 51 and the air backwash valve 21 are closed, the secondary drain valve 41 and the exhaust valve 71 are opened to release the pressure. Then, after closing the secondary drain valve 41 and opening the raw water valve 61 to fill the raw water chamber 6 with raw water, the exhaust valve 71 is closed and the filtration valve 11 is opened to resume the filtration.

  In the simultaneous backwashing of the liquid and the gas of the present invention, the liquid and the gas flow back in the hollow fiber membrane 2 and flow out from the micropores 5 formed on the outer surface of the hollow fiber membrane 2 to the raw water chamber 6 side. The fouling substance that has entered the hole 5 can be removed, and the fouling substance attached to the outer surface of the hollow fiber membrane 2 can be peeled off by swinging the hollow fiber membrane 2. In particular, the fouling substance adhering to the surface in the vicinity of the bonding portion 8 can be easily peeled off by rocking due to the passage of gas through the hollow fiber membrane 2. Further, since the gas discharged from the micropores 5 causes the liquid in the raw water chamber 6 to flow vigorously, the fouling material adhering to the outer surface of the hollow fiber membrane 2 is peeled off and the fouling material accumulated between the hollow fiber membranes 2 is also removed. Can be discharged.

  Further, since the coupling portion 8 on the opening 3 side is erected so that the sealing portion 4 is positioned on the lower side, the liquid and gas that have flowed back in the hollow fiber membrane 2 due to the buoyancy of the gas are directed upward. The fouling substance that is finely dispersed and uniformly flows out of the micropores 5 and adheres to the outer surface of the hollow fiber membrane 2 is uniformly cleaned. Moreover, the fouling substance adhering to the outer surface of the hollow fiber membrane 2 is also peeled off when the liquid flowing out of the hollow fiber membrane 2 from the micropores 5 floats along the vicinity of the surface of the hollow fiber membrane 2 together with the gas. In addition, since the peeled fouling material is swept upward, the fouling material is prevented from reattaching.

  Further, since the liquid and the gas flow upward due to the buoyancy of the gas when flowing back through the hollow fiber membrane 2 from the coupling portion 8, the liquid and the gas are not only from the micropores 5 formed in the vicinity of the coupling portion 8 but also the sealing portion. Also, the fine holes 5 formed in the vicinity of 4 are uniformly discharged.

  Hereinafter, the present invention will be described with reference to specific examples.

In Example 1, a hollow fiber membrane (bubble point 0.05 Mpa) made of polysulfone and having a fractional particle diameter of 2.0 μm was used, and the membrane area of the membrane module was 2 m ² . As raw water, black soil was added to tap water to make the turbidity about 15 degrees, and the raw water was filtered at a membrane filtration flux of 3 m / day for 30 minutes and then washed.

The cleaning method of Example 1 was simultaneous countercurrent cleaning in which water and air were simultaneously introduced, and the raw water chamber side liquid was drained while performing gas countercurrent cleaning with air for 10 seconds after performing simultaneous countercurrent cleaning for 15 seconds. The inflow pressure was set to about 0.15 Mpa for the simultaneous backwashing as in the case of the liquid backwashing alone and the case of the gas backwashing alone. In addition, the cleaning speed at the time of backwashing was about ² Nm ³ / h per 1 m ² of membrane area for gas and about 0.3 m ³ / h per 1 m ² of membrane area for liquid. Note that the back-flow cleaning speed at the start of the gas back-flow cleaning temporarily reached ^{3 to} 6 Nm ³ / h per 1 m ² of membrane area regardless of the above setting. As a result, the cleaning efficiency of the present invention was 80% as shown in FIG.

In calculating the above results, the following calculation formula was used.
Membrane trapped turbid mass (mg): (turbidity concentration of raw water) x (filtered water amount)
Washing wastewater turbid mass (mg): (turbidity concentration of washing wastewater) x (washing wastewater amount)
Washing efficiency (%): (washing wastewater turbid mass) / (membrane trapped turbid mass) × 100

The fractional particle size referred to in the present invention means the particle size (S) of particles having a rejection rate of 90% by the hollow fiber membrane, and the rejection rate of at least two kinds of particles having different particle sizes. Based on the measured value, in the following approximate formula (1), the value of S at which R (%) is 90 is determined, and this is the fractional particle size.
R = 100 / (1−m × exp (−a × log (s))) (1)
In the above formula, a and m are constants determined by the water permeability and structure of the hollow fiber membrane, and are calculated based on measured values of two or more types of rejection.

  In Comparative Example 1, liquid back-flow cleaning with water was performed for 15 seconds, gas back-flow cleaning with air was performed for 15 seconds, and then water on the raw water chamber side was drained while performing gas back-flow cleaning with air for 10 seconds. Other setting conditions are the same as those in the first embodiment. As a result, the cleaning efficiency was 74%.

  In Comparative Example 2, water on the raw water chamber side was drained while performing gas backflow cleaning with air for 30 seconds and then performing gas backflow cleaning with air for 10 seconds. Other setting conditions are the same as those in the first embodiment. As a result, the cleaning efficiency was 66%.

  In Comparative Example 3, water on the raw water chamber side was drained while performing liquid back-flow cleaning with water for 30 seconds and then performing gas back-flow cleaning with air for 10 seconds. Other setting conditions are the same as those in the first embodiment. As a result, the cleaning efficiency was 67%.

  In Example 2, treated water having a turbidity of 0.5 to 1.0 degrees obtained by coagulating and precipitating river water with polyaluminum chloride was used as raw water, and the same apparatus as that of Example 1 was used. Filtration was performed under the conditions of a hollow fiber membrane filtration flux of 5 m / day and a washing interval of 30 minutes, and the transmembrane pressure difference due to change with time was investigated. As a result, the increase rate of the present invention was moderate as shown in FIG. 3, and the transmembrane pressure difference was about 10 kPa even after 10 days. The transmembrane pressure difference used was a value converted to a water temperature correction at 25 ° C.

  In Comparative Example 4, the experimental conditions are the same as in Example 2 except that gas backflow cleaning was performed as the cleaning method. As a result, the transmembrane pressure difference was about 60 kPa at the time point of 10 days after the rising gradient became steep after about 3 days.

  The membrane cleaning method of the present invention can be used in the field of water treatment in which turbidity in water to be treated is treated with a membrane.

It is a schematic block diagram which shows the washing | cleaning method of the hollow fiber membrane module in connection with embodiment of this invention. It is a figure which shows the test result of Example 1 and Comparative Examples 1-3. It is a figure which shows the test result of Example 2 and Comparative Example 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hollow fiber membrane module 2 Hollow fiber membrane 3 Opening part 4 Sealing part 5 Micropore 6 Raw water chamber 7 Filtrated water chamber 8 Joint part 11 Filtration valve
DESCRIPTION OF SYMBOLS 12 Flow pipe 21 Air backwash valve 22 Air compressor 23 Air supply pipe 31 Backwash water tank 32 Backwash pump 33 Water supply pipe 34 Water backwash flow control valve 35 Water backwash valve 41 Secondary drain valve 51 Primary drain valve 61 Raw water valve 71 Exhaust valve A Raw water B Primary drain C Secondary drain D Filtered water E Exhaust

Claims (2)

  A plurality of hollow fiber membranes each having an opening on one end and a sealing portion on the other end and having a large number of micropores formed on the surface are combined on the opening to form a connection, and the filtered water chamber is formed by the connection. In the external pressure type hollow fiber membrane module partitioned into a side and a raw water chamber side, the liquid and gas are introduced simultaneously from the opening toward the raw water chamber side from the filtered water chamber side through the hollow fiber membrane. A method for washing a hollow fiber membrane, comprising washing the hollow fiber membrane.   The method for cleaning a hollow fiber membrane according to claim 1, wherein the external pressure hollow fiber membrane module is erected so that the opening side is positioned downward and the sealing portion side is positioned upward.

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