JP2013180263A - Porous material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous material capable of preventing an organism adhesion.SOLUTION: This porous material comprises crystalline anodized film having a plurality of fine pores penetrated to a thickness direction to be formed by anodization with aluminum or an aluminum alloy, and the zeta potential of the entire surface or one part is less than 0 mV when used.

Description

  Embodiments of the present invention relate to a porous material that can be suitably used for particle removal of organic wastewater containing microorganisms.

  Porous materials with a structure containing a large number of voids inside are used in a wide range of applications such as filters for various fluids, heat insulating materials, sound-absorbing materials, shock-absorbing materials, regardless of their gas phase or liquid phase. ing. In addition to the above physical properties, the internal surface area is large, so that the catalyst support or porous material directly functions as a catalyst, and is used as a chemical reaction field.

  In recent years, for the purpose of fine chemical applications, drinking water production, and other industrial process water production, there are many occasions where filtration of very fine particles is required. Especially in the field of water treatment, examples of using membranes for particle removal are expanding because the apparatus can be made compact and control can be facilitated as compared with conventional precipitation methods and the like.

  As a water treatment technique using a membrane, there is a membrane separation activated sludge treatment method. The membrane separation activated sludge treatment method is a method of separating microorganisms and other solids using a membrane instead of a conventional sedimentation basin after organic matter is decomposed by activated sludge organisms. Compared with the conventional activated sludge method, this method is advantageous in that it can be treated with high-concentration activated sludge microorganisms, the sludge can be easily managed, the apparatus can be made compact, and good treated water quality can be obtained. And is being applied to industrial wastewater treatment and small-scale sewage treatment facilities.

  For membrane separation activated sludge treatment, a microfiltration (MF) membrane or an ultrafiltration (UF) membrane is usually used. As the shape, a hollow fiber membrane or a flat membrane is used, and as the material, a membrane such as polyvinylidene fluoride or polyethylene is mainly used. In membrane separation activated sludge treatment, it is necessary to treat activated sludge microorganisms of high concentration, and therefore particles containing activated sludge microorganisms are likely to accumulate on the membrane. For this reason, resistance to fouling is required.

  In order to suppress fouling of a separation membrane for membrane separation activated sludge treatment, generally, a method is used in which aeration is performed on the surface of the separation membrane, and the particles are peeled off by physical force when bubbles come into contact with each other. Used. However, if the aeration air volume is increased, the energy consumption required for aeration also increases. Therefore, it is desirable that the aeration air volume is small from the economical point of view. In order to reduce the aeration air volume, a film that does not easily cause fouling at the material level is required.

  At that time, a filtration membrane having a pore size of the order of submicron is required. However, in this region, there is a problem that the resistance when the medium passes through the pores is large and the pressure loss of the membrane becomes large. In addition, filtration materials generally composed of organic membranes capture particles in the randomly arranged resin or fiber voids inside the filtration material, so that once captured particles are desorbed. Tends to be difficult and contaminated.

  The present applicants first have a porous material that has a high flux and is hardly contaminated by having pores penetrating from the surface oriented in one direction to the back surface from the viewpoint of increasing the membrane flux and preventing contamination. And a manufacturing technique thereof. In this case, since the pores penetrate in a straight line from the primary side to the secondary side, the path becomes shorter compared to a filtration material composed of a randomly oriented film such as an organic film, and the pressure is reduced. Loss reduction can be expected. Further, in the porous material having this structure, the particles are captured at the surface portion of the pores, and the particles do not enter the inside of the filtration material, so that the effect of being hardly contaminated can be expected.

  As a method of forming pores oriented in one direction, a method using anodizing treatment of a metal material such as aluminum can be given. According to this method, pores having submicron size pore diameters can be formed autonomously. The pore diameter can be controlled by conditions such as the composition of the electrolytic solution and voltage, and a porous material having pores with uniform pore diameter distribution can be obtained. The produced anodic oxide film can be separated from the aluminum substrate by dissolution of the aluminum substrate, peeling treatment from the aluminum substrate by reverse electrolysis, etc., and the separated aluminum anodic oxide film can be used as a filtering material. .

  By subjecting the separated aluminum anodic oxide film to a heat treatment, it can be changed from amorphous to crystalline alumina. When the aluminum anodic oxide film is made of crystalline alumina, particularly α-alumina, chemical stability such as water resistance and chemical resistance is remarkably improved. By making use of this chemical stability, stable use over a long period of time and resistance to chemical cleaning can be obtained, which is promising as a separation membrane for membrane separation activated sludge treatment.

  A factor that determines the likelihood of fouling is the adherence of organisms. Microorganisms are characterized by being negatively charged by dissociation of phosphate groups and carboxyl groups present on the surface. The zeta potential of crystalline alumina is positive in the neutral region and is positively charged. Therefore, since the alumina film and the microorganism attract each other electrostatically, the microorganism is likely to adhere to the surface.

  Conventionally, as a measure for suppressing fouling, a method of controlling the hydrophilicity and charging property of the film surface has been proposed. By improving hydrophilicity, there is an effect of preventing adhesion of hydrophobic contaminants such as humic substances, but there is no effect of preventing adhesion of organic substances having a charge including microorganisms. Therefore, when applied as a separation membrane for membrane separation activated sludge treatment, since a high concentration of microorganisms comes into contact, the effect of suppressing fouling is not sufficient.

JP 2010-64924 A JP 09-299773 A JP 2007-254222 A

  An object of the embodiment is to provide a porous material capable of preventing the attachment of organisms.

  According to the embodiment, the amorphous anodic oxide film having a plurality of pores penetrating in the thickness direction, which is formed by anodizing treatment of aluminum or aluminum alloy, is used. A porous material characterized in that the zeta potential of the part is less than 0 mV can be provided.

The figure for demonstrating the structure of the porous material in this embodiment. The X-ray-diffraction graph of the Almophas structure which has not performed crystallization heat processing. An X-ray diffraction graph of a porous material having a γ-alumina structure subjected to a crystallization heat treatment at 800 ° C. for 2 hours. An X-ray diffraction graph of a porous material having a γ-alumina structure and a δ-alumina structure subjected to crystallization heat treatment at 1000 ° C. for 2 hours. An X-ray diffraction graph of a porous material having an α-alumina structure subjected to crystallization heat treatment at 1200 ° C. for 2 hours. The characteristic view which shows the distance between the center points of the adjacent pore of an aluminum anodic oxide film, and the relationship of an electrolysis voltage. The figure which shows an example of an apparatus structure at the time of using an anodized film for isolation | separation of a membrane separation activated sludge.

Hereinafter, details of this embodiment and other features and advantages will be described in detail.
In the present embodiment, “the entire surface” means all surfaces of the porous material excluding the inner wall surface of the pore. An anodized film having pores aligned in one direction in a self-regular manner is formed by anodizing treatment of aluminum or an aluminum alloy. There are no three-dimensionally complicated voids on the outer surface, and one pore is opened on the outer surface one by one. Therefore, the particles to be separated do not enter the internal voids even if they adhere to the outer surface of the anodized film.

  In this embodiment, the zeta potential can be measured as follows. That is, first, in a state where a solid sample is set in a measurement tank having electrodes at both ends, a certain pressure is applied to flow an electrolyte. As a result, a streaming potential is generated between the electrodes. Next, the zeta potential of the solid sample can be determined by converting the measured streaming potential from the Helmholtz-Smoluchowski equation.

  In this embodiment, since the zeta potential of the entire surface or a part of the surface when used is less than 0 mV, the porous material has a negative charge when it is used, so that the microorganism is negatively charged. Is less likely to adhere. Therefore, when it is used as a separation membrane for membrane separation activated sludge treatment that needs to treat a liquid containing microorganisms at a high concentration, an effect of suppressing fouling can be obtained.

In the present embodiment, the zeta potential is preferably set to −30 mV or less. As described above, the attachment of microorganisms can be suppressed when the zeta potential has a negative charge. However, by increasing the absolute value of the zeta potential, more charges are charged. In order to suppress the adhesion of microorganisms, an electrostatic repulsive force is used, so that it is advantageous that there are many charged charges.
In general, when the absolute value of the zeta potential of the particles exceeds −30 mV, the particles are stably dispersed due to electrostatic repulsion, and by setting the zeta potential of the membrane surface to −30 mV or less, Adhesion can be effectively suppressed.

  In the present embodiment, the pore diameter is preferably 0.5 μm or less. In the membrane separation activated sludge treatment, separation of microorganisms contained in the activated sludge is a function required for the separation membrane. Microorganisms contained in the activated sludge are bacteria, fungi (such as yeast), protozoa, metazoans, etc., and the size is in the range of 1 μm to several 100 μm. In order to prevent leakage of the smallest bacteria, a separation membrane having a pore size smaller than that of bacteria is required. By setting the pore size to 0.5 μm or less, there is a margin compared to the size of bacteria, so it is possible to reliably prevent leakage of bacteria and to process while maintaining a relatively high flux. It becomes.

  The pore diameter is more preferably 0.1 μm or less. From the viewpoint of preventing the leakage of microorganisms, a pore size of 0.5 μm is sufficient as described above, but for particles of 0.5 μm or less such as dead microorganism fragments, earth and sand contained in inflow water, plant fragments, etc. , May be transparent. By setting the pore diameter to 0.1 μm or less, most of these particles can be removed. When it is required to reduce the suspended solid content (SS) of the treated water, it is effective to set the pore diameter to 0.1 μm or less.

  In this embodiment, it is preferable that the zeta potential of the outer surface of the porous material is less than 0 mV. Here, the “outer surface” means all surfaces of the porous material excluding the inner wall surface, bottom and side walls of the pores. In the porous material of the present embodiment, when the pore diameter is smaller than the size of the particle to be removed, the surface opening diameter is also smaller than the removal target particle, and therefore the removal target particle enters the pore. And will adhere to the outer surface of the membrane. By setting the zeta potential on the outer surface in accordance with the particles to be removed, adhesion can be suppressed and promoted.

  In the present embodiment, fine particles smaller than the pore diameter may enter the inside of the pore and adhere to the inner surface of the pore. By making the zeta potential inside the pores less than 0 mV, the effect of suppressing the adhesion of fine particles having charging properties can be obtained.

  In this embodiment, when the porous material is applied as a separation membrane for membrane separation activated sludge treatment, the zeta potential on the outer surface is negative, preferably −30 mV or less in order to suppress the adhesion of microorganisms to the outer surface. Is desirable.

  As described above, when applied as a separation membrane for membrane separation activated sludge treatment, the growing microorganism itself does not enter the pores, but the fragments of dead microorganisms or the macromolecular organic matter produced by the microorganisms The problem is that (extracellular polymer: EPS) adheres. Microorganism fragments are negatively charged because of the presence of phosphate groups and carboxyl groups on the surface, as in live bacteria. As for the extracellular polymer, the polysaccharide, which is the main component, has a hydroxyl group and a carboxyl group, so it is negatively charged. Therefore, by setting the zeta potential inside the pores to be negative, it is possible to suppress the adhesion of substances that cause fouling.

  In this embodiment, it is preferable to apply the porous material to the turbidity treatment of raw water containing microorganisms. As described above, since microorganisms are negatively charged, the adhesion of microorganisms can be effectively suppressed by controlling the zeta potential on the membrane surface to be negative. Therefore, fouling due to the adhesion of microorganisms can be suppressed, and in the treatment of raw water containing microorganisms, a decrease in flux is unlikely to occur.

  In this embodiment, it is preferable to apply the porous material to the microorganism separation membrane of the membrane separation activated sludge treatment apparatus. In the membrane-separated activated sludge treatment, it is necessary to treat water containing a high concentration of activated sludge microorganisms. As described above, by controlling the zeta potential of the membrane surface to less than 0 mV, microorganisms and extracellular It is possible to prevent polymer adhesion. Therefore, when water containing high-concentration activated sludge microorganisms is treated, treatment with a high flux is possible, and the flux is less likely to decrease.

FIG. 1 is a schematic diagram of an anodized film 2 having pores 1 oriented in one direction (vertical direction) produced by anodizing aluminum. Usually, a porous film is formed by performing electrolysis in an electrolytic solution of an acid having an appropriate dissolving power such as sulfuric acid, phosphoric acid, oxalic acid, etc., using aluminum as an anode. The pore 1 is formed by growing a part of the alumina cell 3 while dissolving it vertically from the underlying aluminum. Table 1 below shows typical anodizing conditions.

  After the anodic oxide film 2 is formed by the above method, the base aluminum is removed by mercury (II) chloride coating or dissolution treatment with acid or alkali, whereby only the anodic oxide film can be separated and taken out.

  In the film formed by the anodizing treatment, a layer called the barrier layer, in which the pores 1 do not penetrate, is formed between the porous alumina layer and the underlying metallic aluminum. Also, by gradually lowering the electrolysis voltage during electrolysis of anodization, an anodized film whose barrier layer is gradually thinned is electrolyzed under conditions of opposite polarity, and is peeled off by gas pressure due to hydrogen generation. Only the anodized film can be separated and taken out.

In order for the pores 1 formed by the anodizing treatment to function as through-holes, it is necessary to remove the barrier layer. As a processing method for this purpose, those shown in Table 2 below can be cited. In this way, an anodic oxide film having through holes oriented one-dimensionally can be obtained by anodizing the aluminum substrate, separating from the underlying aluminum, and removing the barrier layer.

  The anodic oxide film thus obtained can be crystallized by heat treatment. Here, an example is shown in which an anodic oxide film (pore diameter: about φ100 to 140 nm, thickness: 100 μm) prepared using phosphoric acid as an electrolytic solution is heat-treated. Immediately after fabrication, it is amorphous as shown in FIG. FIG. 3, FIG. 4, and FIG. 5 show the crystal structure analysis results by X-ray diffraction of the anodic oxide film prepared in the phosphoric acid electrolyte solution after being peeled from the substrate and then heat-treated. As shown in FIG. 3, γ-alumina is heated at 800 ° C. for 2 hours, and γ-alumina and δ-alumina are heated at 1200 ° C. for 2 hours as shown in FIG. Under the heat treatment conditions, α-alumina is formed.

  At this time, since the particles are filtered by the anodic oxide film 2 having the pores 1 having a uniform pore diameter on the surface, particles smaller than the pore diameter of the pores 1 pass through the pores 1 whereas the pores 1 Particles that are equal to or larger than the pore diameter are only trapped on the surface of the pore 1 and do not enter the interior. Therefore, if it is cross flow filtration, it is expected that coarse particles will peel off again.

  The crystalline anodic oxide film 2 thus produced is composed of α alumina or γ alumina. The equipotential points of these materials are about 9.0 for α-alumina and about 8.3 for γ-alumina, and the zeta potential at pH 7 is positive. Therefore, in the range of pH 6-8 assumed by the membrane separation activated sludge process, it will be positively charged and it will be in the condition where microorganisms will adhere easily.

By introducing a functional group having a charge into the surface of alumina constituting the anodic oxide film 2, the zeta potential can be made less than 0 mV. As a method for introducing a functional group onto the surface, a method using a silane coupling agent can be used. The following chemical formula 1 is a chemical formula of the surface of α-alumina having a thiol group introduced using a silane coupling agent. By introducing a thiol group, the zeta potential at pH 7 was -7 mV. Thiol group that -SH dissociates, the α-alumina surface -S ^- because there, since it will have a negative charge, the shift to the negative side of the zeta potential is generated.

  In order to introduce the silane coupling agent into the anodic oxide film 2, an aqueous solution obtained by diluting the silane coupling agent with a solvent such as water, ethanol or methanol is applied to the anodic oxide film 2 and then dried at a predetermined temperature for a predetermined time. Can be used. Moreover, after immersing the anodic oxide film 2 in a solution containing a silane coupling agent, a method of drying at a predetermined temperature for a predetermined time may be used.

By oxidizing the anodic oxide film 2 introduced with the thiol group, it can be converted into a sulfonic acid group, and the zeta potential can be shifted to the negative side. In this case, since the formed sulfonic acid group —SO ₃ H is more easily dissociated than the thiol group, the negative charge amount per surface area of the membrane is further increased. By introducing a sulfonic acid group, the zeta potential at pH was -20 mV. As a result, it becomes possible to more effectively suppress the adhesion of microorganisms. The chemical formula when the sulfonic acid group is introduced is shown in the following chemical formula 2.

  On the other hand, it is known that the pore diameter of an anodized film formed by anodization of aluminum increases in proportion to the electrolysis voltage. It is possible to increase the hole diameter by electrolysis at a high voltage, but if the voltage is too high, discharge occurs and the anodic oxide film is destroyed. For this reason, it is necessary to set an appropriate voltage that can form the anodic oxide film at a practical speed while preventing discharge, but the range of the appropriate voltage varies depending on the type of the electrolytic solution.

  The spacing between adjacent holes is also correlated with the electrolysis voltage. A plot of the distance between the center points of the pores is shown in FIG. The pore diameter of the pores formed by anodizing treatment is smaller than the pore spacing due to the thickness of the alumina cell, but after the anodizing treatment, the pores are expanded by acid, alkali, etc. (pore widening) The hole diameter can be adjusted by applying the treatment.

  As an electrolytic solution generally used for anodizing treatment of aluminum, there are sulfuric acid, oxalic acid, and phosphoric acid. By using these inorganic acids, it becomes possible to produce an anodized film having a pore diameter of 10 to 300 nm. When manufacturing an anodic oxide film having a larger pore size, the electrolytic voltage can be set to 200 V to 400 V by using an organic acid, in particular, a dicarboxylic acid such as malic acid, oxalic acid, succinic acid, or citric acid. It becomes possible. As a result, an anodic oxide film having a pore diameter of 300 nm or more can be obtained.

  FIG. 7 shows an example of the apparatus configuration when the anodic oxide film 2 is used for separation of membrane separation activated sludge. Here, it has the configuration of an outside tank type in which the separation membrane is installed outside the activated sludge treatment tank. The code | symbol 11 in a figure shows the sedimentation tank to which sewage inflow water is supplied. A biological reaction tank 14 including an anoxic tank 12 and an aerobic tank 13 is connected to the precipitation tank 11. An air diffuser 15 is provided at the bottom of the aerobic tank 13, and an air blower 16 is connected to the air diffuser 15. A membrane separation tank 20 containing a membrane module 19 is connected to the aerobic tank 13 of the biological reaction tank 14 via a pipe 18 provided with a water pump 17. The surface of the membrane module 19 has a structure in which an anodized film is formed, and water containing activated sludge microorganisms flows on the outer surface of the anodized film in a direction perpendicular to the penetration direction of the pores. Become. The outer surface of the anodized film has been surface-modified so as to exhibit a negative zeta potential in order to prevent the adhesion of organisms, and therefore, microorganisms hardly adhere to the outer surface of the anodized film. A gas mixing blower 21 is connected to the pipe 18.

  In the apparatus of FIG. 7, sewage inflow water to be treated is introduced into the biological reaction tank 14 after sedimentation and sedimentation of sediment and the like in the sedimentation tank 11. In the biological reaction tank 14, after nitrogen is removed by denitrifying bacteria in the anoxic tank 12, it is sent to the aerobic tank 13, where organic matter is decomposed into carbon dioxide by activated sludge microorganisms, and ammonia generated in the anoxic tank 12. Nitrogen is changed to nitrate ions. The water that has been subjected to biological treatment and has reduced organic components is sent to the membrane separation tank 20 by the water pump 17. At this time, water containing bubbles is sent to the membrane separation tank 20 by mixing the gas by the gas mixing blower 21. Most of the water containing activated sludge microorganisms sent by the water pump 17 is returned to the biological treatment tank 14 as cross-flow water, but a part of it passes through the membrane module 19 to remove the particles. Is obtained. That is, the water containing the activated sludge microorganisms flows from the lateral direction of the modules 19 arranged in the vertical direction, and only the treated water is discharged out of the membrane separation tank 20 through the porous pores.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Fine pore, 2 ... Anodized film, 3 ... Alumina cell, 11 ... Precipitation tank, 12 ... Anoxic tank, 13 ... Aerobic tank, 14 ... Biological reaction tank, 15 ... Air diffuser, 16 ... Air diffuser Blower, 17 ... water pump, 18 ... piping, 19 ... membrane module, 20 ... membrane separation tank, 21 ... gas mixing blower.

Claims (8)

A crystalline anodic oxide film having a plurality of pores penetrating in the thickness direction, formed by anodizing treatment of aluminum or aluminum alloy,
A porous material characterized in that the zeta potential of the entire surface or a part of the surface when used is less than 0 mV.   The porous material according to claim 1, wherein the zeta potential is −30 mV or less.   The porous material according to claim 1 or 2, wherein the pore diameter is 0.5 µm or less.   The porous material according to claim 1, wherein the pore diameter is 0.1 μm or less.   The porous material according to any one of claims 1 to 4, wherein the zeta potential of the outer surface when used is less than 0 mV.   The porous material according to any one of claims 1 to 5, wherein a zeta potential inside the pores when used is less than 0 mV.   The porous material according to any one of claims 1 to 6, which is applied to a turbidity treatment of raw water containing microorganisms.   The porous material according to any one of claims 1 to 7, which is applied to a microorganism separation membrane of a membrane separation activated sludge treatment apparatus.

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