JP3948593B2 - Membrane cleaning method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a membrane in water treatment using a membrane filtration method such as river water, lake water, underground water, etc., raw water for industrial use, sewage, secondary treated water for sewage, industrial wastewater, domestic wastewater, manure, seawater, etc. This relates to a cleaning method.
[0002]
[Prior art]
Conventionally, when raw water as described above is filtered through a membrane, suspended substances and organic substances having a size larger than the pore size of the membrane to be used are blocked by the membrane, and so-called concentration polarization and a cake layer are formed. At the same time, the organic matter in the raw water clogs the membrane or adsorbs to the network inside the membrane. As a result, the filtration flux of the membrane when the raw water is filtered is reduced from a fraction to a few tenths compared with that when the clear water is filtered. The bundle gradually decreases.
[0003]
Of the filtration methods using the hollow fiber membrane module, the so-called external pressure filtration method that filters from the outer surface side of the hollow fiber membrane to the inner surface side is a filtration from the inner surface side of the hollow fiber membrane to the outer surface side. Compared to the internal pressure filtration method, it is possible to secure a large membrane area that contributes to filtration per unit volume, so it is necessary to minimize water production costs, such as turbidity for making waterworks. There is an example used in the field of water treatment, and a filtration method is periodically disclosed in which physical cleaning is periodically performed so that filtrated water can be collected more stably.
[0004]
Specifically, after filtration for a certain period of time, a part of the filtered water is used to flow water from the filtered water side of the membrane to the raw water side in the opposite direction to the filtration, backwashing (hereinafter abbreviated as backwashing). ) By supplying compressed air from the bottom to the top of the hollow fiber membrane module filled with water, the yarn is rocked and the suspended matter accumulated between the hollow fiber membranes is discharged out of the system. There is.
Japanese Patent Application Laid-Open No. 60-19002 discloses a method of arranging a bubble generating nozzle on the side or lower side of the hollow fiber membrane in the hollow fiber membrane storage container together with backwashing and ejecting gas from the nozzle. ing.
[0005]
[Problems to be solved by the invention]
Both the above-described backwashing and air scrubbing are effective techniques for eliminating suspended substances accumulated on the membrane surface and between the membranes, and make the filtration operation more stable. In the method of ejecting gas from the bubble generating nozzle arranged in the module as disclosed in Japanese Patent Application Laid-Open No. 60-19002, it is satisfactory when the generated bubbles are small and the amount of suspended substances accumulated on the membrane surface is large. The cleaning effect cannot be obtained. Therefore, when air scrubbing is performed to introduce gas into the module through the raw water introduction port installed in the module, gas is introduced in the middle of the pipe for sending raw water to the module as in the present application, and a large mass of gas is contained in the module. The membrane is vigorously shaken and the washing is performed efficiently, but the outer surfaces of the membrane are rubbed through the suspended substance, and the membrane surface is crushed, thereby clogging the surface pores and filtering. Operation stability may be impaired. In particular, when the particle size of the accumulated suspended substance is large and the amount accumulated on the membrane surface is large, the above-described intense air scrubbing causes a remarkable phenomenon that the membrane surface is damaged. Furthermore, if the above phenomenon continues, there is a possibility of film breakage.
[0006]
As a result of intensive studies on the film cleaning method, the present inventors have completed the following invention.
The present invention provides: (1) raw water introduced gas pipe to send to the hollow fiber membrane module, the hollow fiber membranes through the raw water inlet port provided on one film edge bonded and fixed portions of the hollow fiber membrane module and at the same time introducing gas into the module, the drainage side of the hollow fiber membranes, by introducing a gas or liquid, external pressure, characterized in that to transmit gas or liquid from the drainage side of the hollow fiber membrane to the raw water side the method of cleaning a filtration hollow fiber membrane, (2) turbid component is a raw water containing particles of 0.1 to 500 [mu] m, the water passing through the membrane between the cleaning and (turbidity of raw water (degree)) × (wash The present invention relates to a method for cleaning an external pressure filtration hollow fiber membrane in which the value (amount (m ³ )) / (membrane surface area (m ² )) is 0.001 or more and the cleaning described in (1) above are alternately performed.
[0007]
Hereinafter, the present invention will be described in detail. The raw water that is the subject of the present invention is river water, lake water, ground water, stored water, secondary sewage treatment water, factory waste water, sewage, and the like. The present invention is larger the particle size of the suspended solids accumulated on the membrane surface during filtration is also the term effective hollow fiber membrane (hereinafter hollow fiber membrane simply film when the amount of accumulating on the surface of the hollow fiber membrane is large ) Cleaning method. If the detergency is inferior in fine air exiting from the gas bubble generating nozzle, a hollow fiber membrane module (hereinafter, a hollow fiber membrane module may be simply referred to as membrane module or modules) raw gas is introduced into the pipe to be sent to the hollow fiber When gas is introduced into the hollow fiber membrane module through the raw water inlet provided on one side of the membrane end adhesive fixing portion of the membrane module, intense air rubbing can be performed with a large mass of gas. In this method, the membrane shakes violently and the cleaning effect is high. On the other hand, the surface of the membrane is rubbed vigorously through suspended substances, and the membrane surface is crushed to clog the surface pores, which makes the filtration operation stable. There is a risk of damage. In order to prevent this, in the present invention, simultaneously with air scrubbing, gas or liquid is introduced into the filtered water side of the membrane, and the gas or liquid is permeated from the filtered water side of the membrane to the raw water side. According to this method, the film surfaces are hardly rubbed and the film surface is not crushed. Each will be described in detail below.
[0008]
[Porous membrane]
As a porous membrane, polyolefin such as polyethylene, polypropylene and polybutene; tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoro Ethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPE), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE) , Fluorine resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); polysulfone, polyethersulfone, polyetherketone, polyetheretherketo , Super engineering plastics such as polyphenylene sulfide; cellulose such as cellulose acetate, ethyl cellulose; polyacrylonitrile, alone and mixtures of these polyvinyl alcohols also include inorganic film such as a ceramic. In particular, a fluorine-based resin film and an inorganic film are preferable because of excellent oxidation resistance, but it is particularly preferable to use a polyvinylidene fluoride (PVDF) film.
[0009]
Among such porous membranes, those whose pore size region is a reverse osmosis membrane, nanofilter, ultrafiltration (UF) membrane, or microfiltration (MF) membrane can be used, but basically have a high filtration flow rate. It is preferable to use an ultrafiltration (UF) membrane or a microfiltration (MF) membrane, and it is particularly preferable to use a microfiltration (MF) membrane. For example, a membrane having an average pore diameter of 0.001 to 1 μm is preferable, and a membrane having an average pore diameter of 0.05 to 1 μm is more preferable.
[0010]
As the shape of the porous membrane, an arbitrary shape such as a hollow fiber shape or a flat membrane shape can be used, but a hollow fiber shape that allows a large membrane area per unit volume is preferable. As the shape of the hollow fiber membrane, there are a straight hollow fiber membrane, a waved hollow fiber membrane, etc., but a waved hollow fiber membrane is preferred for reasons such as turbidity discharge.
In general, filtration is performed using a module containing a membrane.
[0011]
[Membrane module]
The membrane module used in the present invention includes a cartridge type membrane module that is used by being inserted and arranged in a tank having a tube plate or an outer housing in addition to a hollow fiber membrane module connected via a pipe or the like. It is.
Further, examples of the thermosetting resin used for adhesion fixing of both side end portions of the membrane module include epoxy resin, urethane resin, and silicone rubber. Further, by mixing fillers such as silica, carbon black, and carbon fluoride into these resins, the strength of the resin partition walls may be improved and the curing shrinkage may be reduced.
Examples of materials used for the module case of the membrane module include polyolefins such as polyethylene, polypropylene, and polybutene; fluorine resins such as polytetrafluoroethylene (PTFE), PFA, FEP, EPE, ETFE, PCTFE, ECTFE, and PVDF; Chlorine resins such as polyvinyl chloride and polyvinylidene chloride; polysulfone resin, polyether sulfone resin, polyallyl sulfone resin, polyphenyl ether resin, acrylic resin such as PMMA, acrylonitrile-butadiene-styrene copolymer resin (ABS), acrylonitrile -Styrene copolymer resin, polyphenylene sulfide resin, polyamide resin, polycarbonate resin, polyetherketone resin, polyetheretherketone resin alone and mixtures thereof, Beauty, aluminum, and a metal such as stainless steel.
[0012]
A hole for introducing gas for raw water and air scrubbing is provided on one side of the membrane end adhesive fixing portion of the membrane module. The size of the hole is preferably 3 mm or more and 10 cm or less. If the size of the hole is smaller than 3 mm, the size of the bubble introduced into the module is small, the membrane does not shake vigorously during air scrubbing, and if the size of the hole is larger than 10 cm, the number of membranes filled in the module is reduced. Since it lowers, it is not preferable.
[0013]
[Filtering method of porous membrane]
The filtration method may be a whole amount filtration method or a cross flow filtration method.
Moreover, although a pressure filtration system or a negative pressure filtration system may be used, the pressure filtration system is preferable because a higher filtration flux can be obtained.
[0014]
[Porous membrane cleaning method]
In the present invention, air scrubbing that introduces gas into the raw water introduction pipe and introduces gas into the module through the raw water introduction port installed in the module means that gas is directly injected into the raw water introduction pipe without using a gas generation nozzle. Using a simple device, control the size of the raw water inlet installed in the module, change the size of the gas in the module, and raw water or gas mixed with gas during washing between filtrations This refers to the operation of removing and discharging suspended substances accumulated between the membrane surface and the membrane in the module by supplying only the membrane module into the membrane module.
[0015]
In the present invention, reverse flow washing in which gas or liquid is introduced into the filtrate side of the membrane and gas or liquid is permeated from the filtrate side to the raw water side of the membrane is a part of the filtrate obtained by filtering the suspended water. From the filtrate side of the membrane (inner surface side in the case of external pressure filtration) to the raw water side (outer surface side in the case of external pressure filtration). An operation that generates a flow of liquid. In this case, the use of a mixture of gas and liquid is also included.
[0016]
Compared with the method in which gas is introduced into the raw water introduction pipe and gas is introduced into the module via the raw water introduction port installed in the module, a small gas is ejected from the bubble generating nozzle arranged in the module. Therefore, when the air scrubbing is carried out alone, the outer surfaces of the membrane are rubbed more vigorously through the suspended solids. When the membrane surface is crushed, the surface opening may be blocked, and the stability of the filtration operation may be impaired. Especially when the particle size of the particles in the raw water is large, and therefore the particle size of the suspended matter accumulated on the membrane surface during filtration is large and the amount accumulated on the membrane surface is large, the intense air scrubbing as in the present application is performed. When done, the phenomenon is noticeable. Therefore, in the present invention, when performing the above-mentioned air bubbling, at the same time, a gas or liquid is introduced into the filtrate side of the membrane, and reverse flow cleaning is performed so that the gas or liquid permeates from the filtrate side of the membrane to the raw water side. It is essential.
[0017]
The respective times of filtration, air scrubbing, and backwashing can be selected as appropriate, and may be determined as appropriate in consideration of the recoverability of the filtration flow rate and the collected water recovery rate.
Usually, it is preferable to spend 1/10000 to 1/5 of the filtration time between washings for air bubbling and backwashing. If the frequency is less than 1/10000, the washing effect is small, and if the frequency is more than 1/5, the recovery rate of filtrate is poor, which is not preferable.
[0018]
The air scrubbing supply air flow rate per unit time is preferably 0.1 to 20 times the filtration flow rate per unit time in the standard state, and preferably 0.5 to 10 times the flow rate. More preferred. Below these flow rates, the cleaning effect is low, and above these flow rates, there is a possibility of film drying and the like.
The backwashing flow rate per unit time of the backwashing gas, liquid, gas and liquid is 0.01 to 10 times the filtration flow rate per unit time due to the balance between the filtrate recovery rate and the prevention of membrane rubbing. A flow rate of 0.1 to 3 times is particularly preferable. If the flow rate is lower than the backwash flow rate, the effect of preventing the membrane from rubbing is low, and the cleaning effect is also low.If the flow rate is higher than the backwash flow rate per unit time, the recovery rate of the filtrate is lowered. Absent.
[0019]
According to the present invention, when gas is introduced by air scrubbing, it is preferably always performed simultaneously with back-flow cleaning, but only back-flow cleaning may be performed prior to introduction of gas (simultaneously back-flow cleaning). Alternatively, after the introduction of gas (simultaneous backwashing), only backwashing may be performed.
Further, the gas may be introduced while the raw water is introduced at the same time, and the backflow cleaning may be performed at the same time, or the raw water may not be introduced. Alternatively, these may be combined alternately.
Prior to the introduction of gas (simultaneous backwashing), only raw water may be introduced. Alternatively, only raw water may be introduced after the introduction of gas (simultaneous backwashing).
[0020]
[Raw water quality]
The turbid component contained in the raw water of the present invention is a single or mixture of metals such as iron, manganese, aluminum, silicon and their oxides and / or their organic substances such as humic acid, fulvic acid, etc. It refers to agglomerated particles, and the size of the fine particles includes those in the range of 0.1 to 500 μm. River water and the like contain particles with a particle size larger than that. Normally, the raw water introduced into the membrane module is pretreated with a screen mesh or the like, so fine particles exceeding 500 μm are filtered. The possibility of being supplied to the module is very low. The particle diameter of the fine particles referred to in the filtration method of the present invention is a value measured by a laser diffraction / scattering particle size distribution measuring apparatus.
[0021]
Moreover, the turbidity of this invention is a daily average turbidity, and is the value which measured and averaged several days based on JISK0101 9.2.
When air scrubbing that introduces gas into the module through the raw water introduction port installed in the module is performed separately from backwashing, as in this application, When the amount of turbidity accumulated per unit membrane area at the time of performing is large, the membrane surface is more damaged. If the unit membrane area (m ² ) multiplied by the total amount of filtered water (m ³ ) permeated between washings and the turbidity (degree) of the raw water is 0.01 or more, When air scrubbing is performed alone, the membrane surface is damaged, but according to the present invention, high-quality treated water can be obtained with a high membrane filtration flux.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the example of the manufacturing method of the membrane used for this invention and a membrane module, and the example of the filtration method of suspension water are demonstrated.
In addition, the measurement of the turbidity and the particle size in Examples 3 to 6,
Turbidity: As a measuring device, UV-160A, 50 mm cell manufactured by Shimadzu Corporation was used, and a measuring method was performed in accordance with JIS K0101 9.2.
Particle size of fine particles: The measuring device was measured using an LA-910 particle size distribution meter manufactured by Horiba.
[0023]
[Example 1]
(Example of membrane production)
PVDF powder (manufactured by Kureha Chemical Co., KF # 1000), hydrophobic silica (manufactured by Nippon Aerosil Co., Ltd., R-972 [average primary particle diameter 0.016 μm, specific surface area 110 m ² / g, Mw value = 50%]), DOP (manufactured by Chisso Corporation, CS sizer) and DBP (manufactured by Chisso Corporation) are respectively separated by 40.0 / 23.0 / 30.8 / 6.2 parts by weight, mixed with a Henschel mixer, and then with a twin screw extruder, Pellets were made.
[0024]
From the twin screw extruder having the barrel temperature of 260 ° C., the head temperature of 235 ° C., and the spinneret temperature of 230 ° C., the pellets passed through the double spinneret with dimensions of 1.70 mmφ / 0.90 mmφ / 0.50 mmφ, The melt was extruded into a cooling / solidification bath (warm water with a water temperature of 40 ° C.) at a temperature of 40 ° C. 30 cm below the spinning nozzle.
The hollow fiber membrane was wound around a winder, and the hollow fiber membrane bundle was extracted with dichloromethane using the following extraction conditions to extract DOP and DBP.
[0025]
Treatment conditions: room temperature (25-27 ° C.), volume of dichloromethane relative to simple volume of hollow fiber membrane (calculated from inner / outer diameter, length): 20 times amount, treatment time: 5 hours.
Next, the hollow fiber membrane bundle was immersed in a 50% ethanol aqueous solution for 30 minutes, and then a silica solution in the hollow fiber membrane was extracted under the following extraction conditions using a sodium hydroxide aqueous solution having a weight percent concentration of 20%.
Treatment temperature: 60 ° C., volume of the aqueous solution with respect to the simple volume of hollow fiber membrane (inner / outer diameter, calculated from length): 20 times the amount (equivalent ratio to hydrophobic silica is 8 times equivalent), treatment time: 2 hours.
[0026]
Thereafter, warm water washing with 60 ° C. warm water in the same volume as the aqueous sodium hydroxide solution was performed for 1 hour, and this warm water washing was repeated a total of 10 times.
Thus, a hollow fiber porous membrane having an inner / outer diameter of 0.70 / 1.25 mmφ, a porosity of 70%, and an average pore diameter of 0.18 μm was obtained.
[0027]
[Example 2]
(Production example of membrane module)
1800 hollow fiber porous membranes formed in Example 1 were bundled.
Next, after sealing the hollow portion on one side of the bundle, it is housed in a cylindrical module case made of polyvinyl chloride having an inner diameter of 83 mmφ and a length of 1000 mm. On the other end, a total of five polypropylene rods having an outer diameter of 11 mmφ were arranged in parallel with the hollow fiber porous membrane, and then an adhesive jig was attached. The module case with the bonding jig attached on both sides was subjected to centrifugal casting with a two-component epoxy adhesive.
[0028]
After completion of the centrifugal casting, the bonding jig and the polypropylene rod were removed, the bonded end on the side subjected to the sealing treatment was cut, and the hollow portion of the hollow fiber was opened.
A hollow fiber membrane module was produced as described above.
The membrane module was hydrophilized with ethanol, and further subjected to a substitution treatment with water, and then the amount of pure water permeated water was measured.
Thereafter, a leak test was performed with 1 atmosphere of compressed air, but no occurrence of leak was confirmed.
[0029]
[Example 3]
(Example)
Using the hollow fiber membrane module of Example 2, as raw water 1, the turbidity is 0.1 to 5 degrees, the particle size of fine particles in water is 0.9 to 30 μm (median is 9 μm), and the water temperature is 12 ° C. The river surface water was used. As shown in FIG. 1, raw water 1 is pumped to a membrane module 4 by a raw water supply pump 3 through a circulation tank 2, and the filtrate water obtained is stored in a filtrate tank 5. At the time of backwashing, the filtrate in the filtrate tank 5 is sent to the membrane module 4 by the backwash pump 6. The air bubbling was performed by injecting air generated by the compressor 7 into the raw water introduction pipe on the primary side of the membrane module 4.
[0030]
Filtration is a constant flow filtration that supplies raw water 1 to the membrane module 4 at a constant flow rate of 8.4 m ³ / m ² / day. The filtrate was operated at a constant water volume of 4.2 m ³ / m ² / day.
The operating condition was that filtration was performed for 20 minutes, and then backwashing with filtered water was performed for 20 seconds. Backwashing with filtered water and air scrubbing with 2 Nm ³ of air per hour were performed simultaneously for 2 minutes. .
The value of (turbidity (degree) of raw water) × (total amount of filtered water permeating through the membrane between washings (m ³ )) / (membrane surface area (m ² )) was 0.44.
[0031]
The average transmembrane pressure difference after operating for 12 months under the above operating conditions was 1.9 kg / cm ² . Thereafter, the module was removed from the apparatus and a leak test was performed, but no leak was confirmed. The membrane module after operation was disassembled, and the single yarn was chemically washed with a mixture of sodium hypochlorite and caustic soda, and a mixture of oxalic acid and nitric acid. When the outer surface of the membrane was observed with a scanning electron microscope at a magnification of 5,000 times, the outer surface of the membrane was slightly damaged.
[0032]
[Example 4]
(Example)
The same module used in Example 3 was used, and the membrane filtration operation conditions were changed to an operation method in which filtration was performed for 60 minutes, and then backwashing with filtered water and air scrubbing using air were simultaneously performed for 2 minutes. The same experiment as Example 3 was performed except that.
The value of (turbidity (degree) of raw water) × (total amount of filtered water permeating through the membrane between washings (m ³ )) / (membrane surface area (m ² )) was 0.44.
[0033]
The average transmembrane pressure difference after operating for 12 months under the above operating conditions was 2.1 kg / cm ² . Thereafter, the module was removed from the apparatus and a leak test was performed, but no leak was confirmed. The membrane module after operation was disassembled, and the single yarn was chemically washed with a mixture of sodium hypochlorite and caustic soda, and a mixture of oxalic acid and nitric acid. When the outer surface of the membrane was observed with a scanning electron microscope at a magnification of 5,000 times, the outer surface of the membrane was slightly damaged.
[0034]
[Example 5]
(Comparative example)
In Example 3, instead of performing backwashing with filtered water and air scrubbing using air at the same time, scrubbing only with air was performed and the same experiment as in Example 3 was performed.
The transmembrane average pressure difference after 6 months was 2.5 kg / cm ² , and the filtration operation could not be continued any more. The membrane module after operation was disassembled, and the single yarn was chemically washed with a mixture of sodium hypochlorite and caustic soda, and a mixture of oxalic acid and nitric acid. The water permeability was equivalent to 80% of the water permeability. When the outer surface of the membrane was observed with a scanning electron microscope at a magnification of 5,000, the membrane surface was rough and a part of the pores on the membrane surface was blocked, which was presumed to be a cause of a decrease in the amount of permeated water.
[0035]
[Example 6]
(Comparative example)
In Example 5, the same experiment as Example 5 was performed except that raw water 1 was changed to water having a turbidity of 0.1 degree, and the membrane filtration operation conditions were changed to scrubbing only with air after performing filtration for 3 minutes. went.
The value of (turbidity (degree) of raw water) × (total amount of filtered water permeating through the membrane between washings (m ³ )) / (membrane surface area (m ² )) was 0.009.
The transmembrane average differential pressure after operating for 12 months under the above operating conditions was 2.5 kg / cm ² , and the filtration operation could not be continued any further. Thereafter, the module was removed from the apparatus and a leak test was performed, but no leak was confirmed. The membrane module after operation was disassembled, and the single yarn was chemically washed with a mixture of sodium hypochlorite and caustic soda, and a mixture of oxalic acid and nitric acid. When the outer surface of the membrane was observed with a scanning electron microscope at a magnification of 5,000 times, the outer surface of the membrane was slightly damaged.
[0036]
[Example 7]
(Comparative example)
The same module as used in Example 3 was used, except that the compressed air generated by the compressor 7 was passed through a bubble generating nozzle having a nozzle hole diameter of 2 mm installed below the membrane in the module, and air scrubbing was performed. Conducted the same experiment as Example 3. The transmembrane average differential pressure after operating for 3 months under the above operating conditions was 2.5 kg / cm ² , and further filtration operation could not be continued. . Thereafter, the module was removed from the apparatus and a leak test was performed, but no leak was confirmed. The membrane module after operation was disassembled, and the single yarn was chemically washed with a mixture of sodium hypochlorite and caustic soda, and a mixture of oxalic acid and nitric acid. When the outer surface of the membrane was observed with a scanning electron microscope at a magnification of 5,000 times, the outer surface of the membrane was slightly damaged.
[0037]
【The invention's effect】
According to the present invention, cleaning can be performed effectively without damaging the membrane, and as a result, a high membrane filtration flux can be maintained over a long period of time.
[Brief description of the drawings]
FIG. 1 shows an example of a processing flow incorporating a film cleaning method of the present invention.

Claims (1)

At the same time as introducing the gas into the pipe that sends the raw water to the hollow fiber membrane module, and introducing the gas into the hollow fiber membrane module through the raw water inlet provided on one side of the membrane end adhesive fixing part of the hollow fiber membrane module, A method for cleaning an external pressure filtration hollow fiber membrane, wherein a gas or a liquid is introduced into the filtrate side of the hollow fiber membrane, and the gas or liquid is allowed to permeate from the filtrate side of the hollow fiber membrane to the raw water side.

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