JP2008259995A - Cleaning method and filter apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method and a filter apparatus which can reduce lowering of the efficiency of filtering and the performance of the apparatus associated with deterioration of the membrane due to repeated cleaning with a chemical by decreasing the number of times of cleaning with a chemical. <P>SOLUTION: The filter apparatus has a filter 10 containing a hollow fiber membrane 100 which turns into being hydrophilic or hydrophobic depending upon changes of the temperature and/or pH of water supplied and becomes hydrophilic when target raw water is supplied, and a backwashing water production machine 16 which generates raw water for backwashing changing the surface of the hollow fiber membrane 100 into being hydrophilic and supplies the raw water for backwashing to the filter 10 in backwashing the hollow fiber membrane by filtering the raw water so as to remove suspended matter 200 on the surface of the hollow fiber membrane. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cleaning method and a filtration device for filtering surface water and waste liquid using a hollow fiber membrane.

  Raw water that is the target of treatment using a membrane (filter) for wastewater treatment that is used to make surface water such as river water and well water into drinking water and wastewater that is discharged from general industries A water treatment device is used to treat the water. The hollow fiber membrane can process the pore size of the membrane finely, so that a large membrane area can be obtained per unit volume, and it can be used to collect suspensions and microorganisms in raw water that is the subject of filtration. Are better. Since hollow fiber membranes have such characteristics, they are frequently used in water treatment apparatuses.

  On the other hand, in membranes used in water treatment equipment, repeated filtration causes accumulation of minute suspensions and microorganisms on the membrane surface to form a film, increasing differential pressure (constant flow filtration) and decreasing flow rate ( Problems such as constant pressure filtration occur. The suspended matter or the like accumulated on the membrane surface in this manner is periodically removed by physical cleaning or chemical cleaning.

  For example, as shown in FIG. 12A, when the raw water is filtered using the hollow fiber membrane 100, after the suspension 200 contained in the raw water is collected on the outer surface of the hollow fiber membrane 100, The raw water from which the suspension 200 has been removed is discharged through the inside of the hollow fiber membrane 100. In FIG. 12, the flow of the liquid is indicated by arrows.

  The suspension 200 is not accumulated on the membrane surface of the unused hollow fiber membrane 100. Therefore, the unused hollow fiber membrane 100 has a filtration differential pressure (filter medium resistance) due to the thickness of the membrane and the pore structure immediately after passing water. The differential pressure at this time is a suspended matter. Not affected by 200.

  However, when the unused hollow fiber membrane 100 is filtered and passed, the suspension 200 in the raw water is collected in the hollow fiber membrane 100 and suspended on the surface of the hollow fiber membrane 100. Things 200 are accumulated. That is, when the filtration time has elapsed or when a certain amount of raw water has been treated, the suspension 200 accumulates on the membrane surface of the hollow fiber membrane 100, resulting in a differential pressure affected by the suspension 200, The filtration differential pressure increases compared to the state of use.

  When the filtration differential pressure rises, the filtration is stopped, and as shown in FIG. 12 (b), to recover the filtration differential pressure, clear water containing no suspended matter is added from the opposite direction to the filtration. Then, back washing (physical washing) is performed to remove the suspended matter 200 collected and collected on the surface of the hollow fiber membrane 100.

  However, even when backwashing is performed by a conventional method, as shown in FIG. 12 (c), a minute amount of suspension remains on the membrane surface or fine particles enter the pores. At present, it does not recover to the same state.

  For example, FIG. 13 shows an example of the filtration differential pressure when filtration and backwashing are repeated, but a certain period of time has passed since the filtration was started from the state in which the hollow fiber membrane 100 was not used (A in FIG. 13). In this case or when a certain amount of raw water is treated, the suspension 200 accumulates on the membrane surface of the hollow fiber membrane 100 as described above with reference to FIG. 12B, and the filtration differential pressure increases (in FIG. 13). B).

  When backwashing is performed when the filtration differential pressure increases, the suspension 200 is removed from the hollow fiber membrane 100 and the filtration differential pressure decreases to some extent (C in FIG. 13). As described above, since all the suspension 200 accumulated in the hollow fiber membrane 100 cannot be removed, the differential pressure is increased as compared with the differential pressure in the unused state (A in FIG. 13). In addition, when filtration and backwashing are repeated thereafter, the suspension 200 that cannot be removed from the membrane surface of the hollow fiber membrane 100 increases or the membrane surface deteriorates. Along with that, it rises.

  Therefore, when filtration is repeated over a long period of time, in order to remove the suspension 200 accumulated on the membrane surface of the hollow fiber membrane 100, an oxidizing solution such as a strong acid, a strong alkali solution or sodium hypochlorite is used. It is common to wash by immersion (chemical cleaning).

  On the other hand, since chemical cleaning degrades the film, it is desirable to reduce the frequency of chemical cleaning. In order to reduce the frequency of chemical cleaning, improvements are made to the operation of the filtration device that does not increase the filtration differential pressure, the suspension removal method (physical cleaning), the membrane material that makes it easy to remove the suspension, etc. I have been. For example, various techniques for suppressing the accumulation of minute suspensions by improving the material of the membrane or modifying the membrane surface have been studied (see, for example, Patent Documents 1 to 3).

In Patent Document 1, a film that exhibits temperature sensitivity is prepared from polyvinyl alcohol and polyacrylic acid, and a method and a temperature sensitive molecular chain for efficiently washing off a suspension by immersing in warm water at the time of washing to control the pore size. A method is described in which the cleaning efficiency is improved by coating the membrane surface and controlling the pore diameter, thereby suppressing an increase in differential pressure and a decrease in flow rate.
Japanese Unexamined Patent Publication No. 2000-176260 JP 2002-346560 A JP-A-3-32729

  As described above, when chemical cleaning performed to remove suspended matter accumulated on the membrane surface is repeated, the membrane used for filtration deteriorates, and the efficiency and performance of filtration performed after cleaning deteriorates. There is.

  It is an object of the present invention to provide a cleaning method and a filtration device that can reduce a decrease in filtration efficiency and performance due to membrane deterioration due to repeated chemical cleaning by reducing the number of times of chemical cleaning. To do.

  In order to achieve the above object, the cleaning method according to the present invention changes to hydrophilic or hydrophobic at least in accordance with temperature change or pH change of supplied water, and is hydrophilic when raw water to be filtered is supplied. A washing method for washing a filter having a hollow fiber membrane in which a substance capable of being polymerized is coated or coated on the surface of the membrane, the raw water for backwashing for making the membrane surface of the hollow fiber membrane hydrophobic A backwashing process in which the generated raw water for backwashing is supplied to the filter to remove suspension adhering to the membrane surface, and backwash wastewater generated by the backwashing process. A discharge step of discharging from the filter.

  Further, the filtration device according to the present invention has a substance that changes to hydrophilicity or hydrophobicity at least in accordance with temperature change or pH change of supplied water and becomes hydrophilic when raw water to be filtered is supplied. A filter having a hollow fiber membrane polymerized or coated on the membrane surface, and raw water for backwashing that changes the membrane surface of the hollow fiber membrane to be hydrophobic, and generating the raw water for backwashing on the membrane surface And a backwash water producing machine for supplying the backwash raw water generated during backwashing to remove the adhering suspension to the filter.

  According to the present invention, film deterioration due to repeated chemical cleaning can be reduced by reducing the number of times of chemical cleaning.

<First Embodiment>
<Hollow fiber membrane>
A hollow fiber membrane 100 used in a filtration device 1a according to the best embodiment of the present invention will be described with reference to the drawings.

  FIG. 1A shows a schematic diagram of the hollow fiber membrane 100, and FIG. 1B shows a schematic diagram of a part of the hollow fiber membrane 100. FIG. The hollow fiber membrane 100 is polymerized with a molecular chain 100a that changes with environmental changes. Specifically, the hollow fiber membrane 100 according to the best embodiment of the present invention is polymerized with a temperature-sensitive molecular chain 100a whose properties change depending on the temperature change of the surrounding environment. It expands and contracts.

  For example, in the case of the hollow fiber membrane 100 obtained by polymerizing N-isopropylacrylamide, the molecular chain 100a is in an extended state as shown in FIG. Further, when the surrounding environment is a high temperature of 32 ° C. or higher, the molecular chain 100a has a property of contracting as shown in FIG.

  Further, the membrane surface of the hollow fiber membrane 100 expands and contracts due to a temperature change and develops a hydrophilic / hydrophobic change. Specifically, in the case of the hollow fiber membrane 100 obtained by polymerizing N-isopropylacrylamide as described above, the membrane surface becomes a hydrophilic surface 100b as shown in FIG. In a high temperature state at or above C, the membrane surface changes to a hydrophobic surface 100c as shown in FIG. 3 (b).

  In order to suppress the increase in differential pressure due to the accumulation of minute suspensions on the membrane surface, the suspension removal efficiency is improved by considering the binding between the suspension in the water and the membrane surface. be able to. That is, many suspensions present in water have hydrophilic functional groups such as carboxyl groups, hydroxyl groups, and amino groups, and when the membrane surface is hydrophilic, the membrane has a hydrophobic surface. Weak bonds such as hydrogen bonds occur.

  That is, at the time of filtration, the membrane surface of the hollow fiber membrane 100 is made hydrophilic surface 100b, and bonded with weak binding (dotted line in FIG. 4) as shown in FIG. Gather. In addition, by making the surface of the hollow fiber membrane 100 a hydrophobic surface 100c during backwashing, as shown in FIG. 4B, weak hydrogen bonds and the like generated between the membrane surface and the suspension 200 are weak. Since the backwashing is performed after the bond is broken, the removal efficiency can be improved.

  Therefore, the hollow fiber membrane 100 is polymerized with a substance having a hydrophilic property at normal temperature (for example, about 5 to 25 ° C.) of the raw water and a hydrophobic property at a high temperature to make the backwash raw water warm. This facilitates the removal of the suspension 200 accumulated on the surface during filtration.

  In addition, in the hollow fiber membrane 100 mentioned above, although the example which superposed | polymerized the thermosensitive substance was demonstrated, you may coat a thermosensitive substance instead of superposing | polymerizing, or you may produce | generate a film | membrane with a thermosensitive substance.

<Filtration device>
The filtration device 1a according to the first embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 5, the filtration device 1 a includes a filter 10 that filters raw water, a pump 11 that supplies the raw water to the filter 10 during filtration, and a valve 12 that supplies the raw water to the filter 10 by the pump 11. And a pipe 13 and a pipe 14 and a valve 15 for discharging the treated water filtered by the filter 10.

  The filter 10 incorporates a hollow fiber membrane module 101 produced by using the hollow fiber membrane 100 in which the temperature-sensitive substance (molecular chain 100a) described above with reference to FIGS. 1 to 4 is polymerized. ing. The substance polymerized in the hollow fiber membrane 100 becomes hydrophilic when normal temperature raw water to be filtered is supplied into the filter 10, and high temperature backwash raw water is supplied into the filter 10. It is a substance that becomes hydrophobic in some cases.

  The filtration device 1 a supplies the backwash water production machine 16 for producing the backwash water used for backwashing the filter 10 and the backwash raw water produced by the backwash water production machine 16 to the filter 10. Valves 17a and 17b and pipes 18a and 18b. This backwash raw water is hot water at a temperature at which the temperature-sensitive substance becomes hydrophobic when supplied to the filter 10. For example, when N-isopropylacrylamide is polymerized on the hollow fiber membrane 100, the backwash water production machine 16 produces raw water for backwashing that is about 32 ° C. to 37 ° C. when supplied to the filter 10. To do.

  Furthermore, the filtration device 1a is used for discharging the backwash waste water after the backwashing is finished and the suspension 200 is removed from the membrane surface of the hollow fiber membrane 100 by using the backwash when the filtration is started. A valve 19 and a pipe 20 are provided.

  In the filtration device 1a, the opening and closing of the valves 12, 15, 17a, 17b, and 19 are controlled to supply raw water and raw water for backwashing into the filter 10, and discharge treated water and backwash wastewater from the filter 10. To perform filtration and backwashing.

<At filtration>
In the filtration device 1a at the time of filtration, raw water is supplied to the filter 10 by the operation of the pump 11, as shown in FIG. The raw water supplied to the filter 10 is filtered by the hollow fiber membrane module 101. Thereafter, in the filtration device 1a, the treated water from which the suspension 200 in the raw water has been removed by filtration is discharged from the filter 10 and flows out through the pipe 14 and the valve 15.

  At this time, since the valves 12 and 15 are open and the other valves 17a, 17b and 19 are closed, the raw water is supplied to the filter 10 and the filter 10 is connected to the pipe 14 via the pipe 14. It is controlled so that treated water is discharged and raw water and treated water are not discharged to other unnecessary places.

  Thus, by filtration, the suspension 200 is accumulated in the hollow fiber membrane 100 of the hollow fiber membrane module 101, and the differential pressure as described above in FIGS. 12B and 13B is high. It becomes a state.

《When backwashing》
In the filtration device 1a, after a predetermined time has elapsed since the filtration was started, after a predetermined amount of raw water was treated, or when the differential pressure reached a predetermined value, backwashing was performed and accumulated in the hollow fiber membrane 100. Remove suspended suspension 200.

  At the time of backwashing, as shown in FIG. 7, the filtration device 1 a opens the valve 19 and discharges the raw water remaining in the filter 10. At this time, the other valves 12, 15, 17a and 17b are closed.

  When the raw water in the filter 10 is discharged, as shown in FIG. 8, the filtration device 1a is warm water produced by the backwash water production machine 16 while closing the valve 19 and opening the valves 18a and 18b. The backwash raw water is supplied to the filter 10. When backwashing, only the valve 17a is opened and the raw water for backwashing is supplied to the filter 10 only from the pipe 18a. The backwashing raw water is supplied to the filter 10 only from the pipe 18b by opening only the valve 17b. There is a method of opening the valves 17a and 17b and supplying the raw water for backwashing to the filter 10 from the pipes 18a and 18b.

  When supplying the raw water for backwashing only from the piping 18a, the valve 19 is open and the filter 10 does not need to be filled with the raw water for backwashing. On the other hand, when the backwash raw water is supplied from the pipe 18b, the valve 19 is closed, and it is necessary to fill the filter 10 with the backwash raw water to such an extent that the hollow fiber membrane module 102 is immersed in the backwash raw water. is there. At this time, the valves 12 and 15 are closed.

  When the backwashing is completed, as shown in FIG. 9, the filtration device 1 a opens the valve 19 and discharges the backwash waste water from the filter 10. At this time, the valves 12, 15, 17a and 17b are closed.

  When the backwash drainage is discharged, the suspended matter 200 accumulated in the hollow fiber membrane 100 is removed, so that the valves 15, 17a, 17b, and 19 are closed again, and the valve 12 is opened again. A state is reached and filtration is started.

  The change in differential pressure when filtration and backwashing are repeated will be described with reference to FIG. When untreated, the differential pressure between the hollow fiber membrane module (α) in which no temperature-sensitive substance is polymerized and the polymerized hollow fiber membrane module (β, γ) is compared. The hollow fiber membrane module (β, γ) in which is polymerized has a higher differential pressure than the non-polymerized module (α). This is because the temperature-sensitive molecular chain narrows the pores on the membrane surface.

  However, when the raw water for backwashing, which is warm water, is supplied to the filter 10 and the hollow fiber membrane module in which the temperature-sensitive molecular chains are polymerized is changed to hydrophobic, the backwashing differential pressure (β) Therefore, the rate of increase in the differential pressure is lower than that of the module (α) in which the temperature-sensitive molecular chain is not polymerized.

  In addition, even in the case of a hollow fiber membrane module in which temperature-sensitive molecular chains are polymerized, when a backwash in a hydrophilic state is performed with a raw backwash water at a normal temperature without using a high temperature backwash raw water, a differential pressure ( The increase in γ) is high. This is because the membrane surface is in a hydrophilic state even during backwashing, so that the membrane surface and the suspension are bonded, and the suspension cannot be removed sufficiently.

  As described above, in the filtration device 1a according to the first embodiment, the hollow fiber membrane 100 is polymerized with a substance having a hydrophilic property at normal temperature and a hydrophobic property at high temperature, thereby providing raw water for backwashing. Is heated to facilitate removal of the suspension 200 accumulated on the surface during filtration.

  The filtration apparatus 1a can also perform chemical cleaning as in the past, and the chemical supplied to the filter during chemical cleaning is made hydrophobic so that the membrane surface of the hollow fiber membrane becomes hydrophobic like the raw water for backwashing. The cleaning effect can be enhanced by setting the temperature to a high temperature.

<Second Embodiment>
In the hollow fiber membrane used in the filtration device according to the second embodiment, a substance whose properties change due to a change in pH of the surrounding environment is polymerized, and a change in hydrophilicity / hydrophobicity is expressed due to a change in pH. Specifically, the substance that polymerizes into the hollow fiber membrane exhibits hydrophilicity in a neutral region of about pH 7, but is desirably a substance that develops hydrophobicity as it becomes acidic. This is because the raw water is generally neutral at about pH 7. In addition, a substance that expresses such a hydrophilic / hydrophobic change expresses hydrophobicity exponentially as it changes from neutral to acidic.

  A filtering device 1b according to a second embodiment of the present invention will be described with reference to FIG. In the filtration apparatus 1b shown in FIG. 11, about the same structure as the filtration apparatus 1a mentioned above using FIG. 5, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As described above, the hollow fiber membrane module 102 built in the filter 10 of the filtration device 1b is configured by a hollow fiber membrane in which molecular chains that change due to pH change are polymerized. Therefore, the filtration apparatus 1b has the backwash water manufacturing machine 21 which produces | generates acidic backwash raw water. Specifically, the backwash water production machine 21 generates acidic backwash raw water to the extent that the hollow fiber membrane exhibits hydrophobicity at the time of backwashing, and via the valves 17a and 17b and the pipes 18a and 18b, Supply to the filter 10.

  As described above with reference to FIGS. 6 to 9, the process performed in the filtration device 1b is a process in which neutral raw water is filtered and backwashing using acidic backwash raw water is repeated. Description is omitted. Therefore, in the case of filtration, the hollow fiber membrane is neutral, and the suspension 200 is polymerized with a weak bond, and in the case of backwashing, the acidic backwash raw water is supplied to the suspension 200 and the hollow. Washing is performed by cutting the bond with the thread membrane.

  As described above, in the filtration device 1b according to the second embodiment, the hollow fiber membrane 100 is polymerized with a substance having a hydrophilic property when neutral and a hydrophobic property when acidic. By making the raw water for backwashing warm, removal of the suspended matter 200 accumulated on the surface during filtration is facilitated.

  In addition, although the hollow fiber membrane mentioned above demonstrated in the example which superposed | polymerized the temperature sensitive substance, it may coat a temperature sensitive substance instead of superposing | polymerizing, or may produce | generate a film | membrane with a temperature sensitive substance.

  In addition, the filtration apparatus 1b can perform chemical cleaning as in the past. If the hollow fiber membrane changes in hydrophobicity / hydrophilicity depending on the temperature, the chemical supplied to the filter during chemical cleaning is reversed. The cleaning effect can be enhanced by setting the temperature of the membrane of the hollow fiber membrane to be hydrophobic like the raw water for washing.

It is a figure explaining the hollow fiber membrane used for the filtration apparatus concerning a 1st embodiment of the present invention. It is a figure explaining the elasticity of the hollow fiber membrane of FIG. It is a figure explaining the hydrophobicity / hydrophilicity change of the hollow fiber membrane of FIG. It is a figure explaining a mode that a suspension accumulates and is removed by hydrophobicity / hydrophilicity change of a hollow fiber membrane of Drawing 1. It is a figure explaining the filtration apparatus concerning a 1st embodiment of the present invention. It is a figure explaining the process of filtration in the filtration apparatus of FIG. It is a figure explaining the process which switches from filtration to backwashing in the filtration apparatus of FIG. It is a figure explaining the process of backwashing in the filtration apparatus of FIG. It is a figure explaining the process which complete | finished filtration in the filtration apparatus of FIG. It is a figure explaining the change of the filtration differential pressure in the case of repeating filtration and backwashing. It is a figure explaining the filtration apparatus concerning a 2nd embodiment of the present invention. It is a figure explaining the mode of a suspension accumulated when performing filtration and backwashing in a general hollow fiber membrane. It is a figure explaining the change of the filtration differential pressure in the case of repeating filtration and backwashing in a general hollow fiber membrane.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b ... Filtration apparatus 10 ... Filter 11 ... Pump 12, 15, 17a, 17b, 19 ... Valve 13, 14, 18a, 18b, 20 ... Pipe 16, 21 ... Backwash water manufacturing machine 100 ... Hollow fiber membrane 100a ... Molecular chain 100b ... Hydrophilic surface 100c ... Hydrophobic surface 101,102 ... Hollow fiber membrane module 200 ... Suspension

Claims (6)

A hollow fiber in which the membrane surface is polymerized or coated with a substance that changes to hydrophilicity or hydrophobicity with a change in temperature or pH of the supplied water and becomes hydrophilic when raw water to be filtered is supplied. A cleaning method for cleaning a filter having a membrane inside,
A production step of producing raw water for backwashing for changing the membrane surface of the hollow fiber membrane to be hydrophobic;
A backwashing step of supplying the generated raw water for backwashing to the filter to remove suspended matter adhering to the membrane surface;
A discharge step of discharging backwash wastewater generated by the backwash step from the filter;
A cleaning method comprising: The substance is a substance that becomes hydrophilic when the water supplied into the filter is at room temperature and changes to hydrophobic when the water supplied into the filter is at a temperature higher than the room temperature. And
The cleaning method according to claim 1, wherein in the generating step, the high temperature backwash raw water is generated. The substance is a substance that becomes hydrophilic when water supplied into the filter is neutral, and changes to hydrophobic when the water supplied into the filter is acidic,
The cleaning method according to claim 1, wherein in the generation step, the acidic backwash raw water is generated. A hollow fiber in which the membrane surface is polymerized or coated with a substance that changes to hydrophilicity or hydrophobicity with a change in temperature or pH of the supplied water and becomes hydrophilic when raw water to be filtered is supplied. A filter having a membrane inside;
The backwashing raw water generated during backwashing to produce a raw material for backwashing that changes the membrane surface of the hollow fiber membrane to be hydrophobic, and to remove the suspension adhered to the membrane surface. A backwash water production machine to be supplied to the filter;
A filtration apparatus comprising: The substance is a substance that becomes hydrophilic when the water supplied into the filter is at room temperature and changes to hydrophobic when the water supplied into the filter is at a temperature higher than the room temperature. And
The filtration apparatus according to claim 4, wherein the backwashing water producing machine generates the high temperature backwashing raw water. The substance is a substance that becomes hydrophilic when water supplied into the filter is neutral, and changes to hydrophobic when the water supplied into the filter is acidic,
The filtration apparatus according to claim 4, wherein the backwash water producing machine generates the acidic backwash raw water.

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