JP2008012468A - Separation membrane for solid/liquid separation, membrane element, membrane filtration apparatus, and solid/liquid separation method for separating solid from solid-containing liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separation membrane capable of keeping an increase of filtration resistance with time on the surface of the membrane sufficiently small in the process of carrying out solid/liquid separation namely filtrating a solid substance unable to permeate the membrane contained in a liquid to be filtrated by virtue of the separation membrane. <P>SOLUTION: The separation membrane for solid/liquid separation is characterized by having surface roughness of its surface layer of not greater than 0.1 μm and a breakaway coefficient ratio of the substance unable to permeate the membrane of not lower than 4. The separation membrane is further characterized by having filtration resistance upon filtrating pure water of not greater than 5×10<SP>10</SP>/m, a mean pore diameter at the membrane surface of not greater than 0.2 μm and a resistance coefficient ratio of not greater than 1.2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a separation membrane used as a filtration membrane for solid-liquid separation of a solid-containing liquid such as an activated sludge solution or a microorganism culture solution, and a membrane filtration apparatus and a solid-liquid separation method using the separation membrane.

  When solid content liquid such as activated sludge or microbial culture solution is filtered through a separation membrane and solid-liquid separation is performed, the solid content liquid that is the filtrate is brought into contact with the separation membrane and pressurized from the filtrate side or permeate side By making the pressure negative, only the desired liquid component permeates through the separation membrane. At this time, the non-membrane permeable substance contained in the liquid to be filtered adheres to the membrane surface, and the adhered substance causes an increase in membrane filtration resistance. When membrane filtration is continued, the membrane filtration resistance gradually increases. Therefore, when membrane filtration is performed by applying a constant membrane filtration pressure, the membrane filtration flow rate is reduced. Further, when membrane filtration is performed with a constant membrane filtration flow rate, the transmembrane pressure difference increases as the membrane filtration resistance increases. In the former case, the planned flow rate cannot be secured, and in the latter case, more energy is required to increase the pressure and at the same time the burden on the separation membrane increases. Therefore, it is a very important requirement for a separation membrane for solid-liquid separation that non-membrane permeable substances are difficult to adhere to the surface of the separation membrane and that the membrane filtration resistance can be kept small when the filtrate is subjected to membrane filtration. is there.

As such a separation membrane, for example, in Patent Document 1, the surface roughness of the porous resin surface is set to 20 μm or less, preferably 10 μm or less, thereby making it difficult for dirt components to adhere to the membrane surface. It is described that the separation membrane clogging due to the non-membrane permeable substance is less likely to occur. As a specific example, a separation membrane having a surface roughness of 7 to 9 μm is described.
JP 2003-135939 A

  However, when a membrane to be filtered such as activated sludge using a separation membrane having a surface roughness of 7 to 9 μm described in Patent Document 1, it is difficult for non-membrane permeable substances to adhere to the membrane surface. The non-membrane permeable substance once adhered to the membrane surface is difficult to peel off, and it is difficult to sufficiently suppress the increase in membrane filtration resistance with time.

  The object of the present invention is to provide a separation membrane that can maintain a sufficiently small increase in membrane filtration resistance over time when a non-membrane permeable substance contained in a filtrate is subjected to solid-liquid separation by membrane filtration through a separation membrane. Is to provide etc.

The separation membrane for solid-liquid separation of the present invention is characterized in that the surface roughness of the membrane surface layer portion is 0.1 μm or less, and the non-membrane permeable substance peeling coefficient ratio on the membrane surface is 4 or more. is there. Furthermore, it is preferable that the pure water membrane filtration resistance is 5 × 10 ¹⁰ / m or less, the average pore diameter on the membrane surface is 0.2 μm or less, and the filtration resistance coefficient ratio is 1.2 or less. The present invention also includes a separation membrane element having the separation membrane and a membrane filtration device.

  The separation membrane of the present invention is easy to peel off from the surface of the separation membrane once the non-membrane permeable substance adheres to the surface of the separation membrane, so that the increase with time of the amount of non-membrane permeable substance attached to the separation membrane surface is reduced. Can be suppressed. The membrane filtration resistance tends to increase according to the amount of non-membrane permeable substance adhering to the separation membrane surface, so by suppressing the increase in the amount of non-membrane permeable substance adhering to the separation membrane surface to a small amount The increase in membrane filtration resistance can be kept small, and membrane filtration with good operating efficiency can be maintained.

  Further, by setting the pure water membrane filtration resistance to a predetermined level or less, high water permeability can be obtained. Furthermore, by setting the average pore diameter on the membrane surface to a predetermined level or less and the filtration resistance coefficient ratio to a predetermined level or less, it is possible to keep the amount of resistance generated per substance attached to the separation membrane surface small. The resistance at the time of membrane filtration of the liquid to be filtered can be reduced.

  By using such a separation membrane of the present invention, when performing membrane filtration with a constant membrane filtration flow rate, membrane filtration resistance and transmembrane pressure difference can be kept low, and constant membrane filtration pressure When membrane filtration is performed by adding, membrane filtration resistance can be kept low and a high membrane filtration flow rate can be obtained. That is, since the membrane filtration flux can be kept large, the membrane area required to obtain a constant amount of membrane filtrate can be reduced. Also, when membrane filtration is performed while washing the membrane surface by bringing air bubbles into contact with the membrane surface or applying flow to the liquid to be filtered, such as crossflow, The power of the aeration blower for generating and the liquid feed pump for generating the flow can be reduced, and energy saving and cost reduction can be achieved.

  The influence of the pore diameter and surface roughness on the membrane surface of the separation membrane will be described with reference to FIG. FIG. 1 is a cross-sectional structure diagram schematically showing the pore diameter 4 and the surface roughness 3 in order to consider the influence of the pore diameter and the surface roughness in the cross section of the surface layer portion 2 of the separation membrane 1.

  In the separation membrane of the present invention, the surface roughness 3 in the membrane surface layer portion 2 is 0.1 μm or less, and the non-membrane permeable substance peeling coefficient ratio on the membrane surface is 4 or more. Preferably, the surface roughness 3 of the membrane surface layer portion is 0.05 μm or less, and the non-membrane permeable substance peeling coefficient ratio is 10 or more. By satisfying this characteristic, the non-membrane permeable substance adhering to the separation membrane surface is easily peeled off from the membrane surface.

Furthermore, the pure water membrane filtration resistance is preferably 5 × 10 ¹⁰ / m or less, which increases the water permeability of the separation membrane. Moreover, it is also preferable that the average pore diameter 4 on the membrane surface is 0.2 μm or less, more preferably 0.07 μm or less, and the filtration resistance coefficient ratio is 1.2 or less. This reduces the resistance generated even when a non-membrane permeable substance adheres to the membrane surface.

  Here, the separation membrane has a function of capturing a substance having a certain particle diameter or more contained in the filtrate by applying pressure on the filtrate side or sucking from the permeate side, There are dynamic filtration membranes, microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, etc., depending on the difference in the trapped particle size. The separation membrane of the present invention is a microfiltration membrane and an ultrafiltration membrane, preferably a microfiltration membrane. The shape of the separation membrane includes a flat membrane and a hollow fiber membrane, and the shape is not particularly limited, but is preferably a flat membrane.

  Further, the surface roughness of the membrane surface layer portion is an average value of the height in the direction perpendicular to the membrane surface in the surface layer portion where the separation membrane is in contact with the liquid to be filtered. Can be measured.

  An atomic force microscope device (Nanoscope IIIa manufactured by Digital Instruments) is used as a measuring device, a SiN cantilever (manufactured by Digital Instruments) is used as a probe, a scanning mode is a contact mode, a scanning range is 10 μm × 25 μm, and a scanning resolution is 512. The height (Zi) of the Z axis (direction perpendicular to the film surface) of each point is measured as × 512, and data is acquired. Before the measurement, a membrane sample as a sample is immersed in ethanol at room temperature for 15 minutes, then immersed in reverse osmosis membrane filtered water for 24 hours, washed, and then air-dried before use. Moreover, the process which levels the base line of measurement data is performed, and the calculated value by following Formula (1) is made into the surface roughness of a film | membrane surface layer part.

Here, RMS is the surface roughness (μm) of the membrane surface layer part,
Is the average value of Zi (μm), and N is the total number of points.

  The pure water membrane filtration resistance is a membrane filtration resistance value when the separation membrane is subjected to membrane filtration with pure water, and can be measured in the present invention as follows.

  First, the separation membrane to be evaluated is immersed in a 20% ethanol aqueous solution at a temperature of 30 ° C. or more for 2 hours or more. A membrane filtration test apparatus 400 as shown in FIG. 2 is used as an experimental apparatus. The membrane filtration test apparatus 400 pressurizes a pure water chamber 410 containing pure water or a stirring cell 401 (Amicon 8050 manufactured by Millipore Corporation) with nitrogen gas 405 (the pressure is measured by a pressure gauge). In this case, the liquid to be filtered is filtered by the separation membrane 402 installed in the membrane fixing holder 406. In membrane filtration, the liquid to be filtered can be stirred by rotating a stirring bar 404 immersed in the liquid to be filtered by a magnetic stirrer 403. Further, the membrane permeate is received by a beaker 407 placed on an electronic balance 408, the amount of the membrane permeate is measured by the electronic balance 408, and the measured value is taken into the personal computer 409. Moreover, the presence or absence of pressurization of each part of the membrane filtration test apparatus is adjusted by opening and closing the valve 412, the valve 413, and the valve 414.

  Using the membrane filtration test apparatus 400 as described above, the pure water chamber 410 is pressurized with nitrogen gas 405, and pure water is subjected to membrane filtration while supplying pure water to the agitating cell 401. And the data which show the relationship between the obtained time and the amount of membrane filtrate are processed as follows. First, the membrane filtration flux at an arbitrary filtration time is calculated using the differential coefficient of the filtrate amount at an arbitrary filtration time. Next, from the membrane filtration flux at the arbitrary filtration time, the membrane filtration resistance at the arbitrary filtration time is calculated according to the following formula using the membrane filtration pressure.

  The membrane filtration resistance is calculated by the following calculation formula (2).

Here, R is the membrane filtration resistance (1 / m), ΔP is the transmembrane pressure difference (Pa), μ is the permeated water viscosity (Pa · s), and J is the membrane filtration flux (m / s). Here, μ may directly measure the viscosity of the membrane filtrate, but may be converted from the temperature according to the equation (3).

Here, F = 0.01257187, B = −0.005806436, C = 0.001130911, D = −0.000005723952, and T is the absolute temperature [K]. That is, when the Celsius temperature is σ [° C.], it is expressed as T = σ + 273.15.

  From the results calculated as described above, create a relationship between the total filtrate volume per unit membrane area and membrane filtration resistance, and per unit membrane area created from the results of the membrane filtration test using the pure water. From the relationship between the total filtrate amount and the membrane filtration resistance, the membrane filtration resistance at which the membrane filtration resistance is constant is defined as the initial value of the membrane filtration resistance.

  The average pore diameter on the membrane surface is the average value of the pore diameters on the surface of the separation membrane.In the present invention, the surface of the separation membrane is observed with a scanning electron microscope, and from the obtained image, What is necessary is just to measure the pore diameter observed on the surface, and let the average value be an average pore diameter.

  In addition, the non-membrane permeable substance peeling coefficient ratio on the membrane surface is the ratio of the non-membrane permeable substance adhering to the separation membrane that indicates the ease with which the non-membrane permeable substance peels from the separation membrane to the standard membrane. It is the expressed value. That is, the higher the separation coefficient ratio, the easier the non-membrane permeable substance adhering to the separation membrane is peeled from the separation membrane, and the non-membrane permeable substance cake layer is less likely to be formed on the membrane surface, resulting in higher membrane filtration performance. . The filtration resistance coefficient ratio is a value representing the filtration resistance coefficient representing the resistance generation amount per unit substance amount of the non-membrane permeable substance adhering to the membrane surface by the ratio to the standard membrane. Here, the standard membrane is a Durapore membrane (hydrophilic, VVLP02500, pore size 0.10 μm) manufactured by Millipore Corporation.

  The non-membrane permeable substance peeling coefficient and the filtration resistance coefficient can be obtained by the following methods.

  First, in order to obtain the filtration resistance coefficient, the membrane filtration test apparatus 400 of FIG. 2 is used, and the filtrate is subjected to membrane filtration using a separation membrane. Here, an appropriate liquid according to the purpose of use of the separation membrane is used as the liquid to be filtered. For example, when used as a separation membrane for activated sludge, activated sludge is used, and when used as a separation membrane for microorganism culture solution, a microorganism culture solution is used. As the liquid to be filtered, a physically and chemically stable liquid containing a suspended substance may be used.

  In the membrane filtration test apparatus 400, first, the pure water chamber 410 was removed, and the dotted line 415 in FIG. 2 was connected. The separation membrane to be evaluated is placed in the membrane fixing holder 414, the liquid to be filtered is added to the stirring cell 401, and pressurization with nitrogen gas is performed. Here, membrane filtration is performed without stirring by the magnetic stirrer 403. From the data showing the relationship between the time obtained by membrane filtration and the amount of membrane filtrate, a relationship between the total amount of filtrate per unit membrane area and membrane filtration resistance is created as described above. Since the created relationship between the total amount of filtrate per unit membrane area and the membrane filtration resistance includes a straight line portion, the slope of this straight line is designated as ko. Further, when the solid substance amount (dry weight) of the liquid to be filtered is measured and the value is X (mg / L), the filtration resistance coefficient α is obtained by the following equation (4).

The filtration resistance coefficient was measured for a standard film and evaluation film, it calculates the filtration resistance coefficient ratio alpha _r as the following equation (5).

Here, α _m is the filtration resistance coefficient in the evaluation membrane, and α _s is the filtration resistance coefficient in the standard membrane.

  Next, in order to obtain a non-membrane permeable substance peeling coefficient, a membrane filtration test similar to the case of the filtration resistance coefficient is performed. However, in this membrane filtration test, membrane filtration is performed while stirring. At this time, it is preferable to temporarily stop the membrane filtration during the membrane filtration. As a result, the peeling coefficient can be obtained with high accuracy. From the data showing the relationship between the time obtained by membrane filtration and the amount of membrane filtrate, a relationship between the total amount of filtrate per unit membrane area and membrane filtration resistance is created as described above.

  Here, the relationship between the total filtrate amount per unit membrane area and the membrane filtration resistance is reproduced by the following membrane filtration resistance prediction method. In this membrane filtration resistance prediction method, the following mathematical formula is used.

Here, J (t) is the membrane filtration flux (m / s) at time t, R (t) is the membrane filtration resistance (1 / m) at time t, and Xm (t) is the unit membrane area at time t. The amount of solid component substances adhering (g / m ² ), X (t) is the amount of solid component substances (g / m ³ ) in the liquid to be filtered at time t, and γ is the non-membrane permeable substance separation coefficient (1 / m / s), τ is the film detergency (−), λ is the coefficient of friction (1 / Pa), η is the reciprocal of density (m ³ / g), Δt is the step size (s) at time t, and Rm is the film The filtration resistance initial value (1 / m), V (t) is the volume of the liquid to be filtered (m ³ ) at time t, and A is the effective membrane area (m ² ). Also, here, τ = 1, η = 1 × 10 ⁻⁶ , the filtration resistance coefficient α uses α determined above, and Rm uses the pure water membrane filtration resistance determined above.

  By repeating the calculation of the formulas (6) to (10) while updating the time, the values of the membrane filtration flow rate and the membrane filtration resistance at each time are calculated, and the total filtrate amount and the membrane per unit membrane area are calculated. Obtain the predicted value of the relationship with filtration resistance. Here, the predicted value of the relationship between the total filtrate amount per unit membrane area and the membrane filtration resistance when giving various non-membrane permeable substance peeling coefficients and friction coefficients is calculated, and the difference from the actual measurement value is The non-membrane permeable substance peeling coefficient and the friction coefficient that are minimized are determined as the non-membrane permeable substance peeling coefficient and the friction coefficient in the separation membrane. Here, it is preferable that the difference of the predicted value with respect to the actually measured value at each time follows the following equation.

here,
Is the difference between the predicted values (−), R _{msr, i} is the measured value (1 / m) of the membrane filtration resistance at point _i , R _{cal, i} is the calculated value (1 / m) of the membrane filtration resistance at point i, N Is the total number of points (-).

The non-membrane permeable substance peeling coefficient obtained as described above is calculated for the standard film and the evaluation film, and the non-membrane permeable substance peeling coefficient ratio γ _r is calculated by the following equation.

Here, γ _m is the non-membrane permeable substance peeling coefficient in the evaluation membrane, and γ _s is the non-membrane permeable substance peeling coefficient in the standard membrane.

  Next, the manufacturing method of the separation membrane of this invention is demonstrated. The separation membrane of the present invention can be produced, for example, by coagulating a membrane-forming stock solution containing a polyvinylidene fluoride resin and a pore-opening agent in a coagulating solution containing a non-solvent to form a porous separation functional layer. it can.

  At this time, the membrane separation solution may be applied to the surface of the substrate to form a porous separation functional layer, or the substrate may be immersed in the membrane formation solution to form a porous separation functional layer. When applying the film-forming stock solution to the substrate, it may be applied on one side of the substrate or on both sides. Only the porous separation functional layer may be formed separately from the substrate.

  And in coagulating the membrane forming undiluted solution, only the porous separation functional layer formed on the substrate may be brought into contact with the coagulating solution, or the porous separation functional layer may be immersed in the coagulating solution together with the substrate. In order to bring only the porous separation functional layer into contact with the coagulation liquid, for example, a method in which the porous separation functional layer formed on the base material is brought into contact with the coagulation bath surface, glass plate, metal A method in which a base material is brought into contact with a flat plate such as a plate and attached so that the coagulation bath does not enter the base material side, and the base material having a porous separation functional layer is immersed in the coagulation bath together with the plate. is there. In the latter method, the base material may be attached to the plate and then the film of the film-forming stock solution may be formed, or the stock solution film may be formed on the base material and then attached to the plate.

  In addition to the polyvinylidene fluoride resin described above, a pore-opening agent or a solvent for dissolving them may be added to the film-forming stock solution as necessary.

  In the case of adding a pore-opening agent having an action of promoting porous formation to the film-forming stock solution, the pore-opening agent may be any one that can be extracted by the coagulation liquid, and preferably has high solubility in the coagulation liquid. For example, polyoxyalkylenes such as polyethylene glycol and polypropylene glycol, aqueous polymer such as polyvinyl alcohol, polyvinyl butyral, and poracrylic acid, and glycerin can be used.

  In the present invention, as the pore opening agent, a surfactant containing a polyoxyalkylene structure, a fatty acid ester structure or a hydroxyl group can be used. Use of a surfactant makes it easy to obtain the target pore structure.

The polyoxyalkylene _{structure, - (CH 2 CH 2 O} ) n -, - (CH 2 CH 2 (CH 3) O) n -, - (CH 2 CH 2 CH 2 O) n -, - (CH 2 _{CH 2 CH 2 CH 2 O)} n- the like can be mentioned, particularly in view of the hydrophilic _{- (CH 2 CH 2 O)} n-, called polyoxyethylene preferred.

  Examples of the fatty acid ester structure include fatty acids having a long-chain aliphatic group. The long-chain aliphatic group may be linear or branched, and examples of the fatty acid include stearic acid, oleic acid, lauric acid, and palmitic acid. Moreover, fatty acid ester derived from fats and oils, such as beef tallow, palm oil, coconut oil, etc. are also mentioned.

  Examples of the surfactant having a hydroxyl group include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, glycerin, sorbitol, glucose, and sucrose.

  The surfactant used as the pore-opening agent in the present invention preferably contains two or more of a polyoxyalkylene structure, a fatty acid ester structure and a hydroxyl group.

  Of these, surfactants containing all of the polyoxyalkylene structure, fatty acid ester structure and hydroxyl group are particularly preferably used. For example, polyoxyethylene sorbitan fatty acid ester includes polyoxyethylene sorbitan monostearate, polyoxyethylene palm Oil fatty acid sorbitan, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene fatty acid ester, polyethylene glycol monostearate, polyethylene glycol monooleate, polyethylene glycol monolaurate Can be mentioned. These surfactants are particularly preferable because they not only improve the dispersibility of the inorganic fine particles, but also have the characteristics that even if they remain in the porous layer and are dried, the water permeability and blocking properties are not lowered.

  When a solvent for dissolving a polyvinylidene fluoride resin, other organic resin, a pore-opening agent, or the like is used in the film forming stock solution, N-methylpyrrolidone (NMP), N, N- Dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetone, methyl ethyl ketone and the like can be used. Of these, NMP, DMAc, DMF, and DMSO, which are highly soluble in polyvinylidene fluoride resins, can be preferably used.

  In addition, a non-solvent can also be added to the film-forming stock solution. The non-solvent does not dissolve the polyvinylidene fluoride resin or other organic resins, and acts to control the size of the pores by controlling the solidification rate of the polyvinylidene fluoride resin and other organic resins. To do. As the non-solvent, water and alcohols such as methanol and ethanol can be used. Of these, water and methanol are preferred from the viewpoint of ease of wastewater treatment and price. These may be mixed.

  In the composition of the film-forming stock solution, the polyvinylidene fluoride resin is 5 to 30% by weight, the pore-opening agent is 0.1 to 15% by weight, the solvent is 45 to 94.8% by weight, and the non-solvent is It is preferably within the range of 0.1 wt% to 10 wt%. Among them, when the amount of the polyvinylidene fluoride-based resin is extremely small, the strength of the porous layer is lowered, and when it is too large, the water permeability may be lowered. Therefore, the range of 8% by weight to 20% by weight is more preferable. If the amount of the pore-opening agent is too small, the water permeability may decrease, and if the amount is too large, the strength of the porous layer may decrease. In addition, if it is extremely large, it may remain excessively in the polyvinylidene fluoride resin and elute during use, and the quality of the permeated water may deteriorate or the water permeability may change. Therefore, a more preferable range is 0.5 wt% to 10 wt%. Furthermore, if the amount of the solvent is too small, the stock solution is likely to be gelled, and if the amount is too large, the strength of the porous layer is lowered. If the amount of non-solvent is too large, gelation of the stock solution tends to occur, and if it is extremely small, control of the size of pores and macrovoids becomes difficult. Therefore, it is more preferably 0.5 wt% to 5 wt%.

  On the other hand, as the coagulation bath, a non-solvent or a mixed solution containing a non-solvent and a solvent can be used. When a non-solvent is used for the film-forming stock solution, the non-solvent in the coagulation bath is preferably at least 80% by weight of the coagulation bath. If the amount is too small, the solidification rate of the polyvinylidene fluoride-based resin is slowed and the pore diameter is increased. More preferably, it is in the range of 85% by weight to 100% by weight. On the other hand, when a non-solvent is not used for the film-forming stock solution, it is preferable to reduce the content of the non-solvent in the coagulation bath, compared to the case where a non-solvent is also used for the film-forming stock solution. preferable. When the amount of the non-solvent is large, the solidification rate of the polyvinylidene fluoride resin increases, and the surface of the porous layer becomes dense and the water permeability may decrease. More preferably, the range is from 60% to 99% by weight. By adjusting the content of the non-solvent in the coagulation bath, the pore size on the surface of the porous layer and the size of the macrovoids can be controlled. If the temperature of the coagulation bath is too high, the coagulation rate will be too fast. Conversely, if the temperature is too low, the coagulation rate will be too slow, so it is usually selected in the range of 15 ° C to 80 ° C. preferable. More preferably, it is the range of 20 to 60 degreeC.

  The separation membrane of the present invention is particularly preferably an ultrafiltration membrane or a microfiltration membrane. Further, it is more preferable that the rejection of fine particles having an average particle size of 0.088 μm is 90% or more. When this rejection rate is not satisfied, for example, in the treatment of sewage wastewater, bacterial cells and sludge leak, clogging with bacterial cells and sludge occurs, filtration differential pressure increases, and the service life is extremely short. It becomes.

  Here, the blocking rate is the temperature of 25 ° C. of raw water in which polystyrene latex fine particles (nominal particle size 0.088 μm, standard deviation 0.0062 μm) manufactured by Ceradyne are dispersed in reverse osmosis membrane permeated water to a concentration of 10 ppm. From the absorbance of ultraviolet light having a wavelength of 202 nm obtained by allowing the separation membrane to permeate under a pressure of 10 kPa and obtaining the raw water and the permeated water, respectively, the following equation is used.

  The separation membrane of the present invention can be made into a separation membrane element by combining with a support. In the present invention, the form of the separation membrane element is not particularly limited, but the separation membrane element in which the support plate is used as a support and the separation membrane of the present invention is disposed on at least one surface of the support plate is the separation membrane element of the present invention. This is one of the preferred forms. The element of this form can be suitably used for sewage treatment as described below. In this embodiment, since it is difficult to increase the membrane area, it is preferable to provide separation membranes on both sides of the support plate in order to increase the water permeability.

  The present invention also includes a solid content-containing liquid storage tank that stores a solid content-containing liquid, and a separation membrane for solid-liquid separation of the solid content-containing liquid is disposed in the solid content-containing liquid storage tank. A membrane filtration device for solid-liquid separation using the above-described separation membrane of the present invention as a separation membrane and provided with a cleaning means for cleaning the surface of the separation membrane Including.

  Here, the solid content-containing liquid is not particularly limited in its form and use as long as it is a liquid containing solid content. For example, it is an activated sludge liquid used for microbial culture solution and sewage wastewater treatment in the food and medical fields.

  In addition, the cleaning means for cleaning the separation membrane surface is not particularly limited in form as long as it has an effect to peel off the non-membrane permeable substance adhering to the separation membrane surface from the separation membrane surface in the membrane filtration process. However, the liquid to be filtered that comes into contact with the surface of the separation membrane by, for example, aeration from the lower part of the separation membrane and bringing the air valve into contact with the surface of the separation membrane and simultaneously supplying a flow to the liquid to be filtered, And a method of generating shearing stress on the membrane surface by vibrating or moving the separation membrane.

  In addition, as the membrane filtration device here, a submerged membrane filtration device that immerses the separation membrane in the filtrate, and a cross-flow type that performs membrane filtration while feeding the filtrate to the container containing the separation membrane There are membrane filtration devices, rotary membrane filtration devices that rotate the separation membrane by immersing all or part of the separation membrane in the liquid to be filtered. That is, as a method and apparatus that can be preferably applied to the present invention, there are a membrane-separated activated sludge method used for the treatment of sewage, factory effluent, manure and the like, a microbiological substance production process including a membrane separation step, etc. The solid component-containing liquid is solid-liquid separated by performing the solid-liquid separation of the solid component-containing liquid by the membrane filtration device in which the separation membrane element of the present invention is disposed in the solid component-containing liquid containing tank containing the solid component-containing liquid. A separation method is mentioned.

The water permeability and the rejection rate of the separation membrane in the examples were measured as follows.
To measure the water permeability of the separation membrane, cut the separation membrane into a circle with a diameter of 50 mm, set it in a cylindrical filter holder, and pre-permeate the reverse osmosis membrane permeate at 25 ° C. for 5 minutes at a head height of 1 m. Then, the permeated water was sampled for 5 minutes after permeation.

  For the rejection, a calibration curve of the concentration was obtained using latex particles (polystyrene latex fine particles manufactured by Ceradyne, nominal particle size 0.088 μm, standard deviation 0.0062 μm). That is, a separation membrane (diameter 43 mm) was set in a holder for measuring the particle rejection rate (UHP-43K, manufactured by Advantech Toyo Co., Ltd.), raw water adjusted to a latex particle concentration of about 10 ppm was added, and the nitrogen pressure at an evaluation pressure of 10 kPa was added. Then, 25 cc of permeated water was collected while stirring the raw water, and the latex particle concentration of the raw water and the permeated water was measured with a spectrophotometer (U-3200, manufactured by Hitachi, Ltd.). Measured by the absorbance of ultraviolet light at 202 nm, the blocking rate was determined from the concentration ratio by the following formula.

Polyvinylidene fluoride as a main component resin as a polyvinylidene fluoride-based blend resin (PVDF / Kureha Chemical Industry Co., Ltd., KF # 850) resin, and polysulfone as an auxiliary component resin (PS / manufactured by Teijin Amoco Engineering Plastics Co., Ltd., P-3500) Using polyoxyethylene sorbitan monostearate as a pore-opening agent, N, N-dimethylformamide (DMF) as a solvent, and H ₂ O as a non-solvent, respectively, and stirring them sufficiently at a temperature of 95 ° C. A film-forming stock solution having the composition was prepared.

Polyvinylidene fluoride (PVDF): 17.0% by weight
Polyoxyethylene sorbitan monostearate: 8.0% by weight
N, N-dimethylformamide (DMF): 72.0% by weight
H ₂ O: 3.0% by weight

Next, after the film-forming stock solution is cooled to 30 ° C., it is applied to a non-woven fabric made of polyester fiber having a density of 0.48 g / cm ³ and a thickness of 220 μm, and after application, immediately immersed in pure water at 20 ° C. for 5 minutes. The membrane was immersed in hot water at 90 ° C. for 2 minutes to wash away the solvent N, N-dimethylformamide and the pore-opening agent polyoxyethylene sorbitan monostearate to produce a separation membrane.

Next, when the rejection of the latex fine particles having an average particle size of 0.088 μm was measured for the obtained separation membrane, it was a high value of 99.2%. Moreover, the water permeability was 42.3 × 10 ⁻⁹ m ³ / m ² · s · Pa.
Further, the surface structure of the separation membrane was observed by a scanning electron microscope to be the film surface structure as shown in the electron micrograph (magnification 60,000) shown in FIG.

  For the separation membrane, the standard membrane, and the two types of commercially available separation membranes, the surface roughness of the surface layer, the average pore diameter, the pure water membrane filtration resistance, the non-membrane permeable substance peeling coefficient ratio, and the filtration resistance coefficient ratio are as follows: Measurement was performed according to the method.

  The surface roughness of the surface layer is measured by using an atomic force microscope (Digital Instruments Nanoscope IIIa) as a measuring device, using a SiN cantilever (Digital Instruments) as a probe, scanning mode is contact mode, and scanning range is 10 μm × 25 μm, scanning resolution was 512 × 512, and the height (Zi) of each point in the Z axis (perpendicular to the film surface) was measured to obtain data. Before the measurement, a membrane sample as a sample was immersed in ethanol at room temperature for 15 minutes, then immersed in reverse osmosis membrane filtered water for 24 hours, washed, and then air dried. Moreover, the process which leveled the base line of measurement data was performed, and the surface roughness of the film | membrane surface layer part was computed based on above-described Formula (1).

  Moreover, the pure water membrane filtration resistance was measured as follows.

  The membrane filtration test apparatus 400 (FIG. 2) was used as an experimental apparatus. The separation membrane to be evaluated was immersed in a 20% aqueous ethanol solution at a temperature of 40 ° C. for 2 hours or more, then thoroughly washed with pure water, set on the membrane fixing holder 406, and pure water chamber 410 by nitrogen gas 405. The pure water was filtered through a membrane while supplying pure water to the stirring cell 401. And the data which show the relationship between the obtained time and the amount of membrane filtrate were processed as follows. First, the membrane filtration flux at any filtration time was calculated using the differential coefficient of the filtrate amount at any filtration time. Next, from the membrane filtration flux at the arbitrary filtration time, the membrane filtration resistance at the arbitrary filtration time was calculated according to the above-described equation (2) using the membrane filtration pressure. The permeated water viscosity was calculated according to the above-described equation (3).

  From the results calculated as described above, create a relationship between the total filtrate volume per unit membrane area and membrane filtration resistance, and per unit membrane area created from the results of the membrane filtration test using the pure water. From the relationship between the total filtrate amount and the membrane filtration resistance, the membrane filtration resistance at which the membrane filtration resistance became constant was defined as the initial value of the membrane filtration resistance.

  The average pore diameter on the membrane surface is determined by observing the surface of the separation membrane by observation with a scanning electron microscope, measuring the pore diameter observed on the surface of the separation membrane from the obtained image, and calculating the average value as the average pore diameter. It was.

  Moreover, the non-membrane permeable substance peeling coefficient and the filtration resistance coefficient were calculated | required with the following method.

  First, in order to obtain | require a filtration resistance coefficient, the to-be-filtered liquid was membrane-filtered using the separation membrane using the membrane filtration test apparatus 400 of FIG. Here, activated sludge used in sewage wastewater treatment was used as the liquid to be filtered. In the membrane filtration test apparatus 400, first, the pure water chamber 410 was removed, and the dotted line 415 in FIG. 2 was connected. The separation membrane to be evaluated was placed in the membrane fixing holder 414, the filtrate to be filtered was added to the stirring cell 401, pressurized with nitrogen gas (20 kPa), and membrane filtration was performed without stirring by the magnetic stirrer 403. From the data showing the relationship between the time obtained by membrane filtration and the amount of membrane filtrate, the relationship between the total filtrate amount per unit membrane area and membrane filtration resistance was created in the same manner as described above, and the above-described equation (4) The filtration resistance coefficient was calculated according to Moreover, the solid component density | concentration of activated sludge was calculated | required by measuring MLSS (dry sludge weight), and was 6465 mg / L. Moreover, the filtration resistance coefficient ratio with respect to the standard membrane was calculated according to the above-described equation (5).

  Next, a membrane filtration test similar to the filtration resistance coefficient was performed in order to obtain a non-membrane permeable substance peeling coefficient. However, in this membrane filtration test, membrane filtration was performed while stirring at 600 rpm, and when the amount of the filtrate reached 5 mL, membrane filtration was stopped for 1 minute (stirring was continued). From the data showing the relationship between the time obtained by membrane filtration and the amount of membrane filtrate, a relationship between the total amount of filtrate per unit membrane area and membrane filtration resistance was created as described above.

Next, the membrane filtration resistance was reproduced by the membrane filtration resistance prediction method based on the above-described equations (6) to (10). Here, ΔP = 20 kPa, temperature 25.1 ° C., V (0) = 1.2 × 10 ⁻⁵ (m ³ ), film area A = 4.1 × 10 ⁻⁴ (m ² ), Xm (0) = 0, τ = 1, η = 1 × 10 ⁻⁶ , the filtration resistance coefficient α is α determined as described above, and Rm is the pure water membrane filtration resistance determined above. Here, in each separation membrane, various values of the separation coefficient γ and the friction coefficient λ are given, and a predicted value of the relationship between the total filtrate amount per unit membrane area and the membrane filtration resistance is calculated. The separation coefficient and the friction coefficient that minimize the difference between the two are determined as the separation coefficient and the friction coefficient in the separation membrane. In addition, the difference of the predicted value with respect to the actually measured value at each time was in accordance with the above-described equation (11). Moreover, the peeling coefficient ratio with respect to the standard film was calculated according to the above-described equation (12).

  In the examples, the separation membrane used for the evaluation was a separation membrane produced by the above-described method, a standard membrane (Durapore membrane manufactured by Millipore Corporation (hydrophilic, VVLP02500, pore size 0.10 μm)), a commercially available membrane A, a commercially available membrane. Four types of membrane B (all flat membranes). Table 1 shows the surface roughness, average pore diameter, pure water membrane filtration resistance, non-membrane permeable substance peeling coefficient ratio, and filtration resistance coefficient ratio of the four kinds of membranes.

The manufactured membrane has a surface layer surface roughness of 0.1 μm or less, an average pore diameter of 0.2 μm or less, a pure water membrane filtration resistance of 5 × 10 ¹⁰ / m or less, a non-membrane permeable substance peeling coefficient ratio of 4 or more, and filtration. The resistance coefficient ratio is 1.2 or more.

Here, the separation membrane element 100 having a structure as shown in FIG. 4 was produced by bonding and fixing the separation membrane 101 to the support 102 for the production membrane and the commercial membrane A. The separation membrane element 100 was manufactured using a manufactured membrane and a commercial membrane A, and installed in a membrane filtration device 500 as shown in FIG. The membrane filtration device 500 is a submerged membrane separation activated sludge device, and is a wastewater treatment device for treating agricultural settlement wastewater. The agricultural village wastewater, which is the raw water 506, was intermittently charged into an activated sludge storage tank 501 that is a filtrate storage tank having an effective capacity of 2.3 m ³ . Activated sludge is accommodated in the activated sludge storage tank 501 as the filtrate to be filtered 504, and the separation membrane module 502 in which the separation membrane elements 100 are arranged in the vertical direction at regular intervals is immersed in the filtrate to be filtered 504, and the separation is performed. A diffuser tube 507 is installed below the membrane module 502, and air is supplied to the diffuser tube 507 from an aeration blower 503 as a cleaning means. That is, in this apparatus, since the air bubbles supplied from the diffuser tube 507 come into contact with the membrane surface, and the activated sludge flows due to aeration, the adhering components on the membrane surface are separated from the membrane. It will be. Further, the membrane permeate was obtained by a suction pump 505 installed on the membrane permeate side.

  In the membrane filtration apparatus 500, the activated sludge was subjected to membrane filtration with an average membrane filtration flux of 0.6 m / d using the manufactured membrane and the commercially available membrane A. As a result, the behavior of the transmembrane pressure difference as shown in FIG. 6 was obtained. The produced membrane can maintain a lower transmembrane pressure than the commercially available membrane A, and can be said to be a separation membrane suitable for sludge membrane filtration.

FIG. 3 is a cross-sectional structure diagram schematically showing the pore diameter and surface roughness on the membrane surface of the separation membrane. It is the schematic which shows the membrane filtration test apparatus used in order to determine the pure water membrane filtration resistance in this invention, a non-membrane permeable substance peeling coefficient, and a filtration resistance coefficient. It is the photograph which image | photographed the surface of the separation membrane manufactured in the Example with the scanning electron microscope. It is a schematic assembly drawing which shows the structure of the separation membrane element manufactured in the Example. It is the schematic of the membrane filtration apparatus used in the Example. It is a figure which shows the time-dependent change of the transmembrane differential pressure in a manufacture film | membrane and the commercial film | membrane A.

Explanation of symbols

1: Separation membrane 2: Membrane surface layer portion 3: Surface roughness of membrane surface layer portion 4: Pore diameter in membrane surface layer portion 100: Separation membrane element 101: Separation membrane 102: Support body 400: Membrane filtration test apparatus 401: Stirring cell 402: Separation membrane 403: Magnetic stirrer 404: Stirrer 405: Nitrogen gas 406: Membrane fixing holder 407: Beaker 408: Electronic scale 409: Personal computer 410: Pure water chamber 411: Pressure gauge 412, 413, 414: Valve 500: Membrane Filtration device 501: Activated sludge storage tank 502: Separation membrane module 503: Aeration blower 504: Filtration liquid 505: Suction pump 506: Raw water 507: Air diffuser

Claims (6)

A separation membrane for solid-liquid separation, wherein the surface roughness of the surface portion of the membrane is 0.1 μm or less, and the non-membrane permeable substance peeling coefficient ratio on the membrane surface is 4 or more. The pure water membrane filtration resistance is 5 × 10 ¹⁰ / m or less, the average pore diameter on the membrane surface is 0.2 μm or less, and the filtration resistance coefficient ratio is 1.2 or less. 2. A separation membrane for solid-liquid separation according to 1. The surface roughness of the membrane surface layer portion is 0.05 μm or less, the non-membrane permeable substance peeling coefficient ratio on the membrane surface is 10 or more, and the average pore diameter on the membrane surface is 0.07 μm or less. Or the separation membrane for solid-liquid separation of 2. The separation membrane element formed by arrange | positioning the separation membrane in any one of Claims 1-3 as a filtration membrane for solid-liquid separation. A membrane filtration device comprising a filtered liquid storage tank for storing a solid-containing liquid, and a separation membrane for solid-liquid separation of the solid-containing liquid, which is disposed in the filtered liquid storage tank, A separation membrane is the separation membrane according to any one of claims 1 to 3, and a cleaning means for cleaning the surface of the separation membrane is provided. . A solid content-containing liquid is obtained by performing solid-liquid separation of the solid content liquid by a membrane filtration device in which the separation membrane element according to claim 5 is disposed in a filtrate containing tank containing the solid content liquid. Solid-liquid separation method.