JP2001089574A - Polyvinyl alcohol-based water-containing gel, its production and drainage treating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyvinyl alcohol (PVA)-based water-containing gel excellent in capturing property for microorganisms and living property of them and also excellent in endurance such as abrasion resistance and mechanical strength, and provide its method of production and a waste water treating device. SOLUTION: This PVA-based water-containing gel is made to have a structure constituted of an outer layer having many fine holes having a crevasse like state, and an inner layer having a compact three dimensional network structure. Such a water-containing gel is produced by adding a substance capable of making a phase separation of a polymer solution to a polymer solution containing a vinyl alcohol-based polymer having >=3,000 degree of polymerization and a polymer capable of forming a gel by making a contact with a cation to prepare a phase separated solution, bringing the phase separated solution with a cation-containing liquid to solidify at least the surface of the polymer of the phase separated liquid, then forming the gel by bringing the solidified material in contact with a coagulating liquid having a coagulating function to the vinyl alcohol-based polymer and performing an acetal forming treatment. Such gel is preferably used for a waste water treating device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyvinyl alcohol-based hydrogel (hereinafter, polyvinyl alcohol is referred to as PVA).
Abbreviated as "), and a method for producing the same and a wastewater treatment apparatus. More specifically, the present invention relates to a PVA-based hydrogel comprising an outer layer having a crevice-like microporous surface on the surface and an inner layer having a dense three-dimensional network structure, a method for producing the same, and a wastewater treatment apparatus. Since the PVA-based hydrogel of the present invention has excellent durability such as mechanical strength and abrasion resistance, it is preferably applied to wastewater treatment equipment used under severe conditions such as high-speed stirring and deep tanks.

[0002]

2. Description of the Related Art Polymer gels have been actively studied as carriers for biocatalysts, water-retaining agents, cooling agents, substitutes for biogels for eyes, skin, joints, etc., sustained-release materials for drugs, and base materials for actuators. ing. Agar, alginate, carrageenan, polyacrylamide, PVA, photocurable resin, and the like are known as the polymer material used as a raw material of the hydrogel, and among these, mechanical strength is high and hydrophilicity (hydrous,
PVA-based hydrated gels are being studied because they are excellent in microbial habitability and the like. In particular, attention has been paid to the use of such hydrated gels as carriers and biocatalysts in which microorganisms are immobilized.

[0003]

The hydrogel used as a carrier for immobilizing microorganisms is required to be able to retain microorganisms and water at a high level and to have a high ability to capture microorganisms and fine substances. However, various studies have been made to further improve these required performances. For example, JP-A-7-4
No. 1516 discloses that an aqueous solution containing PVA and sodium alginate is contacted with an aqueous solution of calcium chloride or the like to solidify and mold at least the surface of sodium alginate, and then freeze-thaw to form a gel.
A method of producing a PVA-based hydrogel by contacting with a VA coagulation liquid and gelling the same is disclosed.

However, a hydrogel that has been gelled by bringing an aqueous solution containing PVA and sodium alginate into contact with a PVA coagulation solution has a low surface-capturing property for microorganisms due to its smooth surface, and has been gelled by freeze-thawing treatment. Has crater-like irregularities formed on the surface, but the irregularities do not communicate with the inside of the gel, and since a dense layer exists near the surface of the gel, microorganisms cannot enter the inside of the gel. Can only live on the surface.

[0005] JP-A-63-17904 discloses PV
When a mixed aqueous solution composed of A and a natural gelation accelerator (such as sodium chloride) is dispersed and ball-formed in an organic solvent such as toluene to form a natural gel, PVA precipitates from the mixed aqueous solution and undergoes phase separation to form a heterogeneous structure. It is disclosed that by taking the above, macroporous PVA particles can be obtained. However, even by such a method, as described above, only a hydrogel having a smooth surface as obtained by contacting with a PVA coagulation bath can be obtained.

[0006] JP-A-63-276488 discloses that P
It is disclosed that sodium bicarbonate or the like is added to a VA aqueous solution or the like to generate fine bubbles, which are subjected to a freeze-thaw treatment to gel the PVA, but the pores formed by the bubbles are 100 μm or more. Due to their extremely large size, microorganisms can easily enter the interior but are not carried for a long time.

[0007] JP-A-7-251190 discloses a PV
A method is described in which a mixed solution consisting of A and sodium alginate is dropped into an aqueous calcium chloride solution mixed with short fibers to produce a gel having short fibers implanted on the surface in a whisker-like manner. However, when short fibers are adhered by such a method, the gel properties are reduced, and since the fibers are present in a whisker-like manner, the gels are easily entangled with each other and the gel is easily damaged. Since it cannot be formed, the improvement of the ability to capture microorganisms and the like is insufficient.

[0008] By the way, there is a literature in the prior art which suggests a suitable range for the degree of polymerization of PVA used for the production of PVA-based hydrogel and the degree of acetalization of the hydrogel. JP-A-10-204204 discloses the degree of polymerization of PVA used for producing porous spherical particles having interconnected pores having a skeleton of a polyvinyl acetal resin.
If the average degree of polymerization is less than 500, it is difficult to obtain one having a high porosity, and if it exceeds 3800, the viscosity becomes high when dissolved in water, and it becomes difficult to handle in a process such as kneading. It is described that those having a degree of polymerization of 500 to 3800 are preferably used (00
(Refer to paragraph 52) Further, it is stated that the degree of acetalization of the porous spherical particles is good in terms of resistance to microbial erosion when the content is 30 to 85 mol% (0028).
Paragraph). In addition, in JP-A-10-204204, PVA used in Examples and Comparative Examples
Have a polymerization degree of 1500. The degree of acetalization of Examples and Comparative Examples is not shown.

Japanese Patent Application Laid-Open No. 10-263576 discloses that the degree of polymerization of PVA used in the production of hydrogel is from 1000 or more, particularly 1500 or more, from the viewpoints of strength, water resistance and the like. It is described that the gel is preferably used (see paragraph 0020), and the degree of acetalization of the hydrogel is from 10 to 65 mol%, especially from 30 to 65 mol%, from the viewpoints of water resistance and microbial habitability of the gel. 6
It is stated that it is preferably 0 mol% (see paragraph 0047). JP-A-10-263576 discloses a PV used in Examples and Comparative Examples.
A is a polymerization degree of 1700 (Examples 1, 3, Comparative Examples 1, 2,
3) and a degree of polymerization of 4000 (Example 2), and the degree of acetalization of the hydrogel was 39% (Example 1), 37%
(Example 2), 35% (Example 3), 40% (Comparative Example 1), and 0% (Comparative Examples 2, 3).

[0010] Japanese Patent Application Laid-Open No. 10-263 by the present applicant.
The PVA-based hydrogel according to the invention disclosed in Japanese Patent No. 576 sufficiently exhibits its function in wastewater treatment under ordinary conditions. However, even when PVA having an average degree of polymerization of 1000 or more is used for the production of a hydrogel, if the hydrogel has a low degree of acetalization, when used under severe conditions, such as under vigorous stirring or in a deep tank, the abrasion resistance is poor. However, it was not always satisfactory in terms of durability such as mechanical strength.

[0011] Therefore, an object of the present invention is to provide excellent properties such as microbial capture and habitability, as well as abrasion resistance,
An object of the present invention is to provide a highly durable PVA-based hydrogel having excellent mechanical strength, a method for producing the same, and a wastewater treatment apparatus using the hydrogel.

[0012]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above object, and have reached the present invention. That is, the present invention is a PVA-based hydrogel comprising an outer layer having a crevice-like microporous surface and an inner layer having a dense three-dimensional network structure.

[0013] Another invention of the present invention is a method wherein the degree of polymerization is 30.
00 or more vinyl alcohol polymer (A polymer)
And a polymer solution (substance C) capable of phase-separating the polymer solution is added to a polymer solution containing a polymer (B polymer) that gels by contact with a cation to prepare a phase separation solution.
After contacting the phase separation liquid with a cation-containing liquid to solidify at least the B polymer on the surface of the phase separation liquid, the obtained solid is contacted with a coagulation liquid having a coagulation ability for a vinyl alcohol-based polymer to form a gel. At the same time as gelation and / or
Or, in performing acetalization treatment after gelation, 50
% Is a method for producing a PVA-based hydrogel, which is subjected to an acetalization treatment for a time equal to or longer than a time at which the degree of acetalization is obtained.

[0014] The invention of the present application relating to a method for producing a PVA-based hydrous gel comprises (1) using a vinyl alcohol-based polymer having a degree of polymerization of 3000 or more; (2) acetalizing simultaneously with and / or after gelation. When processing, 5
It is characterized in that the acetalization treatment is performed for a long time exceeding the time at which the degree of acetalization of 0% or more is obtained.

PVA used to make hydrogels
By using those having an average degree of polymerization of 3,000 or more, a PVA-based hydrogel excellent in strength, water resistance and the like can be obtained. From the viewpoint of processability and cost, the upper limit of the average degree of polymerization of PVA is 20,000 or less, especially 10,000 or less.
More preferably, VA is used. From the viewpoint of water resistance and the like, the saponification degree is preferably at least 95 mol%, particularly preferably at least 98%, and more preferably at least 99.8 mol%.

By performing acetalization treatment simultaneously with and / or after gelation, as described later, each phase shrinks to form gaps, so that crevasse-like micropores or pores forming a three-dimensional network structure are formed. Is formed, but by increasing the degree of acetalization to 50% or more, the gap becomes large, and more micropores and pores are formed. That is, by using a vinyl alcohol-based polymer having a polymerization degree of 3,000 or more, in producing a PVA-based hydrogel, the degree of acetalization is increased to 50% or more.
A PVA-based hydrogel composed of an outer layer having a crevice-like microporous surface and an inner layer having a dense three-dimensional network structure can be easily produced. The PVA-based hydrogel having a crevice-like microporous formed on the surface thereof is excellent in mechanical strength and abrasion resistance due to easy capture of microorganisms and a dense three-dimensional network structure inside the gel. The degree of acetalization of PVA is 50 to 80 mol%, especially 5 to 80 mol%, in view of the water resistance and microbial habitability of the gel.
The content is preferably 5 to 75 mol%. The degree of acetalization can be controlled by the concentration of aldehyde compound and acid, reaction time, temperature and the like.

The crevasse-like microporous material of the PVA-based hydrogel of the present invention, which is composed of an outer layer having a crevice-like microporous surface on the surface and an inner layer having a dense three-dimensional network structure, is characterized by a scanning electron microscope (SEM). (SEM), fine cracks of irregular shape were observed as microporous on the surface of the gel,
A structure in which the micropores communicate with the inside of the gel.

Since the shape of the crevasses is indefinite, the shape of the crevasses cannot be clearly defined.
In order for the water-containing gel to be excellent in capturing and inhabiting microorganisms, the water-containing gel is freeze-dried, the surface of the gel is observed with a 50.3-fold SEM, and an SEM photograph of any part of the surface is obtained. In the above, it is preferable that at least 5 or more micropores are recognized in a square having a side of 500 μm.
Further, the opening ratio of the gel surface is preferably 1 to 10%. The aperture ratio of the gel surface can be determined by enlarging the SEM photograph to 200% and extracting the microporous portion using commercially available image analysis software. FIG. 1 shows that the hydrogel of the present invention was freeze-dried and the surface of the gel was adjusted to 50.3.
FIG. 2 is a photograph observed with a SEM at × magnification, and FIG.
It is a photograph observed by EM. The thickness of the outer layer is not particularly limited, but if it is too thin, it will be peeled off at the beginning of stirring when it is charged into the wastewater treatment device and stirred, and if it is too thick, it tends to have poor durability. So 10
It is preferable that the thickness is about 30 μm.

The inner layer of the PVA hydrogel of the present invention has a dense three-dimensional network structure. The dense three-dimensional network structure refers to a structure in which crevasse-shaped micropores on the gel surface communicate with the inside of the gel, and the communication holes are three-dimensionally interconnected. The pore size of the communicating hole of the hydrogel can be measured by a mercury intrusion method. The mercury intrusion method is a method in which a gel sample evacuated is immersed in mercury, the pressure applied to the mercury is increased, and the pore diameter is determined from the relationship between the amount of mercury that has entered the pores and the pressure. FIG. 3 shows a mercury intrusion curve 1 and a pore distribution curve 2 obtained by measuring the hydrogel of the present invention by a mercury intrusion method. The mercury intrusion curve 1 is a curve showing the relationship between the mercury intrusion volume into the pores and the pore diameter, and the pore distribution curve 2 is obtained by differentiating the mercury intrusion curve 1. FIG. 3 shows the results of measurement performed twice. The pore size of the micropores of the hydrogel of the present invention is
Measured by such a conventionally known mercury intrusion method,
It is preferable that it is less than the viewpoint of mechanical strength. FIG. 3 is an example in which the pore size distribution of the hydrogel has a maximum at 8 μm.

The structure of the inner layer does not need to be uniform, and may differ in its portions. The inner layer does not need to be a single layer, but may be composed of a plurality of layers. One composed of a plurality of layers may have better habitat of microorganisms. Since the inner layer of the PVA-based hydrogel of the present invention has a dense three-dimensional network structure, microorganisms can easily enter the inside of the gel from the microporous surface of the gel and have good habitability. From the viewpoint of abrasion resistance, the thickness of the inner layer is preferably 95% or more of the maximum diameter of the gel. FIG.
Shows that the cross section of the PVA-based hydrogel of the present invention is 50.3 times S
It is a photograph observed by EM.

According to another aspect of the present invention, at least a biocatalyst in which microorganisms are immobilized is charged, and an organic substance and / or
Or in a wastewater treatment device consisting of a wastewater treatment tank that decomposes and removes inorganic substances, a carrier for immobilizing microorganisms is composed of an outer layer having a crevasse-like microporous surface and an inner layer having a dense three-dimensional network structure. It is a waste water treatment device which is a constituted PVA-based hydrogel.

When the PVA-based hydrogel of the present invention is used as a carrier, and a microorganism is immobilized and used as a biocatalyst, a micropore of crevasse is formed on the surface, so that the microorganism can be easily captured. Since the inside is made of a dense three-dimensional mesh structure, it has excellent mechanical strength and wear resistance. Therefore, when a biocatalyst in which microorganisms are immobilized using the PVA-based hydrogel of the present invention as a carrier is introduced into a wastewater treatment device to perform wastewater treatment, anaerobic bacteria inhabit inside the gel, and aerobic bacteria are present in the outer layer and the inner layer. Inhabitation of。 can provide more excellent purification ability.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The PVA-based polymer used in the PVA-based hydrogel of the present invention is obtained by saponifying a polyvinyl carboxylate such as polyvinyl acetate or polyvinyl pivalate or a copolymer thereof. be able to. It can also be obtained by decomposing homopolymers or copolymers (including block copolymers and graft copolymers) of vinyl ethers such as t-butyl vinyl ether, trimethylsilyl vinyl ether and benzyl vinyl ether.

Examples of comonomer units constituting the copolymer include olefins such as ethylene, propylene, 1-butene and isobutene, acrylic acid and salts thereof,
Methyl acrylate, ethyl acrylate, acrylic acid n-
Propyl, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate,
2-ethylhexyl acrylate, dodecyl acrylate,
Acrylates such as octadecyl acrylate,
Methacrylic acid and its salts, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, t-butyl methacrylate Methacrylic esters such as 2-ethylhexyl, dodecyl methacrylate, octadecyl methacrylate, acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and the like Acrylamide derivatives such as salts, acrylamidopropyldimethylamine and its salts and quaternary salts, N-methylolacrylamide and its derivatives,
Methacrylamide, N-methylmethacrylamide, N-
Ethyl methacrylamide, N, N-dimethyl methacrylamide, diacetone methacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts and quaternary salts, N-methylol methacrylamide and its derivatives Methacrylamide derivatives, methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, i-butyl vinyl ether, t-
Vinyl ethers such as butyl vinyl ether, benzyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride; vinylidene chloride;
Vinyl halides such as vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts and esters; itaconic acid and its salts and esters; vinylsilyl compounds such as vinyltrimethoxysilane; and acetic acid Isopropenyl and the like can be exemplified, and they can be used without impairing the purpose of the present invention.

The shape of the hydrogel can be a desired shape such as a sphere, an ellipse, a fiber, a die, a film, a column, a hollow cylinder, a square, a rod, and an irregular shape. When the PVA-based hydrogel of the present invention is used as a carrier for immobilizing a biocatalyst, it is preferably spherical in view of durability, filling effect, fluidity in a wastewater treatment tank, handleability, and the like. . The maximum diameter of the gel at this time is 1 to 10 m
m, and more preferably 3 to 5 mm, from the viewpoints of separability from sludge, microbial activity and the like.

As described later, a predetermined amount of the PVA-based hydrogel of the present invention is put into a 2 liter tall beaker having # 80 sandpaper adhered to the inner wall thereof, and is subjected to predetermined stirring in water. A gel having a volume retention of 50% or more, preferably 70% or more after 14 days is desirable in terms of abrasion resistance and mechanical strength. Volume retention is
It refers to the ratio of the volume of the hydrogel to the initially charged hydrogel, excluding the portion worn by stirring from the hydrogel initially charged. When the water-containing gel of the present invention is used for wastewater treatment, the water content is preferably higher, but from the viewpoint of strength, it is 50% by weight or more, especially 60% by weight on a wet basis.
It is desirable that the content is not less than 90% by weight and not less than 90% by weight.

The PVA-based hydrogel of the present invention has abrasion resistance,
It shows excellent effects in terms of mechanical strength and is preferably applied to wastewater treatment, but may be used by drying at least a part of the water contained in the hydrogel, and once dried, re-use in water. It may be immersed for use. By removing at least a part of the water, the weight is reduced and the transportation becomes easy. Of course, the gel may be used not only in a hydrous state but also in a state other than a hydrous state. In the present invention, "water-containing" is not limited to only a state containing water,
It also includes conditions that include mixtures of water with other liquids and / or solids.

As described above, the PVA-based hydrogel of the present invention is preferably used for immobilizing microorganisms and treating wastewater as a biocatalyst. It also shows excellent effects as a carrier and a filter medium for a reactor, and also has an excellent effect as a packing material for chromatography since the surface area is remarkably increased. Further, since a crevasse-like microporous surface layer is formed and the number of voids is increased, high water retention is secured, and excellent effects as a cold insulating material and a water retaining material are exhibited.

The polymer (B polymer) which gels upon contact with a cation, preferably a polyvalent metal ion, includes:
Preferred are polyethylene glycol and its derivatives, water-soluble synthetic polymers such as water-soluble polyurethane, alginic acid and its salts, and water-soluble polymer polysaccharides such as carrageenan, mannan and chitosan. Of course, a plurality of these may be used in combination as long as the effects of the present invention are not impaired. Of these, water-soluble high molecular polysaccharides often have the property of gelling upon contact with cations,
It is particularly preferable because it has excellent moldability. Alternatively, itaconic acid-modified or maleic acid-modified PVA modified with a functional group having a coagulation ability for cations may be used as the B polymer. Of these, alkali metal salts of alginic acid, particularly sodium alginate, are suitable in terms of moldability and network structure formation.

The concentration of the A polymer in the polymer solution is preferably higher from the viewpoint of the strength of the gel base material, and is preferably lower from the viewpoint of microbial habitability. Therefore, the solution concentration of the A polymer is preferably 1 to 40% by weight, more preferably 3 to 20% by weight. From the viewpoint of gel moldability, the solution concentration of the B polymer is 0.2 to 4% by weight, further 0.5 to 2% by weight.
It is preferred that

The compounding ratio (weight ratio) of the A polymer and the B polymer should be 100 / 0.2 to 30, preferably about 100/1 to 20 in view of moldability, network structure forming property, gel strength and the like. Preferably, the polymer concentration is about 1 to 50% by weight. In the present invention, it is preferable to use a mixed solution containing the A polymer and the B polymer, but of course, a polymer other than the A polymer and the B polymer, an additive, and the like may be added as necessary. For example, a microorganism medium, a reinforcing material for increasing the strength of the gel, a filler for adjusting the specific gravity, and the like may be added.

As the solvent, water is usually used in terms of processability and the like, but various aqueous solutions of the solvent may be used depending on the case. Examples of such a solvent include alcohols such as ethylene glycol, glycerin and polyethylene glycol, dimethylsulfoxide, dimethylformamide, diethylenetriamine and the like.
Species or a mixture of two or more can be used. Further, an aqueous solution of a rhodanate may be used. When a solvent whose main component is water is used, it is preferable to use a water-soluble polymer as the B polymer, particularly a water-soluble high molecular polysaccharide.
The solution temperature is 1 in terms of the thermal stability of the polymer and the solution viscosity.
It is preferably about 0 to 100 ° C, particularly preferably about 20 to 80 ° C.

In forming the outer layer of the PVA-based hydrogel of the present invention, it is extremely important to phase-separate the mixed solution containing the A polymer and the B polymer. From the above, a substance (substance C) capable of phase-separating these polymers is added to the mixed liquid containing the A polymer and the B polymer to produce a phase separation liquid. The substance C is not particularly limited, but salts can be suitably used. Of these, salts containing a divalent or higher valent anion are preferred because a small amount of the polymer causes phase separation of the polymer and little influence on the moldability and acetalization. In this case, it is particularly preferable to use sodium alginate as the polymer B that gels upon contact with a polyvalent metal ion from the viewpoint of gel-forming properties and phase-separation liquid-forming properties.

Specific examples of salts include sodium carbonate,
Carbonates such as potassium carbonate, calcium carbonate, ammonium carbonate and magnesium carbonate; hydrogen carbonates such as sodium hydrogen carbonate, potassium hydrogen carbonate, ammonium hydrogen carbonate, calcium hydrogen carbonate and magnesium hydrogen carbonate; sodium sulfate, potassium sulfate, ammonium sulfate and sulfuric acid Sulfates such as magnesium; and phosphates such as sodium phosphate, potassium phosphate, ammonium phosphate and magnesium phosphate. A halide salt such as sodium chloride and potassium chloride may be used. These may be used in combination of two or more. Particularly, it is more preferable to use bicarbonate or sulfate in view of solubility, cost, and little residue after the molding step. When sodium alginate is used as the B polymer, it is preferable to use sodium hydrogen carbonate and / or sodium sulfate as the substance C.

The amount of the substance capable of phase-separating the polymer is as follows:
It is preferable that the amount is about 0.01 to 1% by weight based on the polymer solution. The phase separation referred to in the present invention refers to a phenomenon in which a substance C is added to a homogeneous solution containing at least an A polymer and a B polymer to separate into a plurality of solution phases having a specific composition. Such a mixture is called a phase separation liquid. In the phase separation, the absorbance in a state where the substance C is added to a solution containing at least the A polymer and the B polymer and sufficiently mixed is measured using an absorption spectrometer (660 nm), and the relationship between the added amount of the substance C and the absorbance is determined. When plotted, it can be confirmed by the sharp increase in the rate of increase in absorbance. In addition, it can be confirmed by visually observing that the mixture is separated into two or more layers after being left at 60 ° C. for 1 to 7 days. In terms of processability, etc.,
It is preferable to add the substance C to the mixed aqueous solution of the A polymer and the B polymer, but of course, the order of addition may be changed.

In order to adjust the size of the crevasse-shaped microporous material, the opening ratio, and the size of the fine pores in the inner layer, the degree of phase separation, the blending ratio / viscosity ratio of the polymer, the mixing conditions, the temperature of the mixed solution, What is necessary is just to adjust the kind and addition amount of the substance C, solidification temperature, etc. In addition, for example, when the A polymer is PVA (polymerization degree 4000, saponification degree 99.5 mol%) and the B polymer is sodium alginate,
A mixed phase of a polymer and a B polymer,
It consists of a substantially single phase of the polymer. At this time, it is presumed that by approximating the viscosity, interfacial energy, specific gravity, and the like between the separated phases, fine dispersion occurs and the diameter of the crevasse-like microporous material constituting the outer layer decreases.

Next, the obtained phase separation liquid is brought into contact with a cation-containing liquid, preferably a polyvalent metal ion-containing liquid. At this time, it is preferable to thoroughly mix the phase separation liquid to form a uniform dispersion and then contact the cation-containing liquid in order to make the gel structure uniform. Examples of the cation used include calcium ion, magnesium ion, strontium ion,
Examples thereof include alkaline earth metal ions such as barium ions, polyvalent metal ions such as aluminum ions, nickel ions, and cerium ions, potassium ions, and ammonium ions, and a plurality of these may be used.
As the solvent, water is usually used in view of processability.

From the viewpoints of cost, handleability, gel forming property, etc.
It is more preferable to use calcium chloride for the A polymer, and when the B polymer is used in combination with sodium alginate, a gel having excellent moldability and having crevasse-like microporous formed on the surface is obtained. It is particularly preferably used. The cation concentration is 0.05
From about 1 mol / l, especially about 0.1 to 0.5 mol / l, it is preferable in terms of gel moldability and the like.

By bringing the phase separation liquid into contact with the cation-containing liquid, at least the B polymer present on the surface of the phase separation liquid is solidified to form a gel. When it is desired to make the gel spherical, a spherical gel can be easily obtained by dropping or spraying the phase separation liquid on the cation-containing liquid due to surface tension. At this time, it is preferable that the solution is dropped using an extrusion nozzle. The diameter of the extrusion nozzle may be appropriately set, and a diameter of about 1 to 10 mm may be used.

Next, this is brought into contact with a coagulating liquid to gel the inside to obtain a desired gel. In the previous step, at least the surface B polymer was solidified,
The A polymer gels by contacting with the coagulating liquid to obtain a gel composed of the A polymer and the B polymer,
Preferably, the gel of the present invention can be obtained by removing part or all of the B polymer contained in the gel.

The method of removing the B polymer is not particularly limited as long as the A polymer is not dissolved, and may be treated with an aqueous solution containing an alkali metal salt or left for a long time to be decomposed by microorganisms. For example, the B polymer can be almost completely removed by immersing the molded product in an aqueous sodium hydroxide solution (1 mol / liter, 30 ° C.) for 24 hours.

By removing the B polymer, more crevasse-like microporous layers are formed in the outer layer, and the pore volume of a three-dimensional network structure in which micropores are interconnected also increases inside the gel, In addition, excellent effects can also be obtained in terms of microbial adhesion, habitability, liquid permeability, and the like. In order to sufficiently exhibit such effects, it is preferable to remove 50% by weight or more, particularly 80% by weight or more of the B polymer, but in some cases, the B polymer may be used without substantially removing it. Even if some or all of the B polymer remains at the beginning of use, the B polymer is removed by microorganisms or alkalis with the passage of time. It may be provided according to.

Although the reason why the crevasse-like microporosity is formed in the outer layer and the mechanism in which the three-dimensional network structure in which the micropores are interconnected in the inner layer cannot always be clearly explained, as described above. The phase separation liquid of A polymer and B polymer is composed of a mixed phase composed of A polymer and B polymer and a single phase composed of only A polymer.
The mixed phase consisting of about 1 wt% of A polymer and about 2 wt% of B polymer and the single phase consisting of about 10 wt% of A polymer, which is considered to affect the durability, continuously penetrate into each other and become in close contact with each other. However, by contact with the cation-containing liquid, the mixed phase is immobilized,
By the acetalization treatment, it is considered that each phase shrinks to form gaps, so that crevasse-like microporous or pores constituting a three-dimensional network structure are formed. Further, by removing the B polymer, It is presumed that the portion where the B polymer was present becomes a gap, and more micropores and pores are formed.

Examples of the coagulating liquid having a coagulating ability for the vinyl alcohol-based polymer include sodium sulfate, ammonium sulfate, potassium sulfate, magnesium sulfate, aluminum sulfate, sodium citrate, ammonium citrate, potassium citrate, magnesium citrate, and citric acid. Liquids containing at least one of compounds such as aluminum oxide, sodium tartrate, ammonium tartrate, potassium tartrate, magnesium tartrate, aluminum tartrate, etc. can be given. From the viewpoint of high coagulation ability, it is preferable to use an aqueous solution of sodium sulfate. preferable. The concentration is preferably 50 g / L or more, particularly preferably 100 g / L or more, and more preferably a saturated aqueous sodium sulfate solution.

In order to improve the water resistance of the PVA-based gel, a treatment such as a cross-linking treatment may be performed at any step in the production process. In particular, it is preferable to introduce an acetalization treatment in which the treatment operation is simple and the water resistance is greatly improved. The acetalization treatment may be performed in any step, but is preferably performed simultaneously with and / or after the coagulation (gelation) with the coagulation liquid. From the viewpoint of processability, it is preferable to perform the acetalization treatment simultaneously with the coagulation. preferable.

For the acetalization treatment, it is preferable to use an aqueous solution containing an aldehyde compound and an acid. However, from the viewpoint of processability, an aldehyde compound is blended in the coagulation liquid and the acetalization treatment is performed simultaneously with coagulation (gelation). Is preferred. In this case, the swelling or dissolution of the hydrogel in the presence of the aldehyde compound or the acid can be effectively prevented by the presence of the PVA coagulating liquid, so that a more excellent effect is obtained.

The aldehyde compounds include glyoxal, formaldehyde, benzaldehyde, succinaldehyde, malondialdehyde, glutaraldehyde,
Various aldehyde compounds such as adipaldehyde, terephthalaldehyde, nonandial, or acetalized products thereof can be suitably used, and formaldehyde, glyoxal, malondialdehyde or acetalized products thereof, and glutaraldehyde are particularly preferred.

As the acid, a strong acid such as sulfuric acid, hydrochloric acid and nitric acid, a weak acid such as acetic acid, formic acid, oxalic acid and phosphoric acid and an acid salt such as sodium hydrogen sulfate and ammonium hydrogen sulfate can be used. Among these, it is preferable to use a strong acid, especially sulfuric acid.

When the acetalization treatment is carried out, for example, with formaldehyde and sulfuric acid after coagulation, the concentration of the aldehyde compound in the reaction solution is preferably 0.01 g / l or more, and the acid concentration is preferably 0.5 to 300 g / l. When the acetalization treatment is performed simultaneously with coagulation, the concentration of the aldehyde compound is preferably 0.05 to 200 g / l and the acid concentration is preferably 1 to 100 g / l. In this case, when sodium sulfate is used as a coagulant, The concentration of sodium sulfate is preferably 10 to 300 g / liter, and the temperature of the treatment liquid is preferably 10 to 80 ° C.

When the PVA-based hydrogel of the present invention is used as a bioreactor carrier or the like, it is preferable to subject the coagulated (acetalized in some cases) gel to washing and neutralization. In particular, when the biocatalyst is used as a carrier for immobilization, it is preferable to sufficiently wash the biocatalyst since the presence of an aldehyde compound reduces the habitability of microorganisms.

The hydrogel of the present invention has a crevasse-like microporous surface formed on its surface, and has a large surface area and an excellent water retention effect, so that it can be used for all purposes. For example, filter media (solid suspension removal materials, etc.), water retention materials, cold insulation materials, substitutes for biogels such as eyes, skin, joints, etc., sustained release materials for drugs, base materials for actuators, packing materials for chromatography, sewage purification Can be used for materials. Above all, it is preferable to immobilize enzymes and microorganisms to form a biocatalyst and to use them in a wastewater treatment tank since they are excellent in capturing and inhabiting microorganisms.

When the microorganisms are immobilized on the PVA-based hydrogel of the present invention, the immobilization method is not particularly limited, and an inclusive immobilization method in which the microorganisms are mixed in a mixed solution in advance may be employed. When a treatment that adversely affects the biocatalyst such as an acetalization treatment is performed later, it is preferable to attach the biocatalyst after the gel is produced. The type of microorganism is not particularly limited, and may be any of bacteria, actinomycetes, molds, yeasts, and the like, and includes pure culture, mixed culture, and activated sludge.

As a specific example of the microorganism, Mucor (Mucc
or) genus, Fusarium genus, Cladoturix (Cl
adothrix) genus, Sphaerotilus genus, Zooglea genus, Leptomitus genus, Leptomitus genus, Aspergillus genus, Rhizopus
Genus, Pseudomonas, Acetobacter
(Acetobacter) genus, Streptomyces
Genus, Escherichia, Saccharomyces
Examples include microorganisms belonging to genera such as the genus (Saccharomyces) and the genus Candida. In addition, sulfur bacteria,
Examples also include methane bacteria, butyric bacteria, lactic acid bacteria, Bacillus subtilis, deformed bacteria, incomplete bacteria, nitrate bacteria, nitrite bacteria, and denitrifying bacteria.

When the PVA-based hydrogel of the present invention is used for wastewater treatment, it is preferable to immobilize a bacterium that produces a protease, a carbohydrate-decomposition enzyme, or a lipolytic enzyme on the hydrogel. Specific examples of such bacteria include nitrifying bacteria and the like as aerobic bacteria, and denitrifying bacteria, sulfate-reducing bacteria, and methane bacteria as anaerobic bacteria. Regardless of the origin of the enzyme, an enzyme derived from an animal or a microorganism may be appropriately selected.

FIG. 6 shows a wastewater treatment apparatus according to the present invention, which comprises at least a wastewater treatment tank into which a biocatalyst in which microorganisms are immobilized is charged and organic and / or inorganic substances in the wastewater are decomposed and removed. Acetalated PVA of the present invention
It is an example of a wastewater treatment apparatus using a substance in which microorganisms are immobilized on a system hydrogel as a biocatalyst, and is a flowchart in the case of decomposing and removing organic substances in wastewater under aerobic conditions. First, waste water 1 is supplied to a waste water treatment tank 2 from a first sedimentation tank (not shown). In the wastewater treatment tank 2, acetalized PVA hydrogel 3 is previously charged into wastewater at the lower limit of operation, and is fluidized by the air diffuser 4 provided at the bottom of the wastewater treatment tank 2. Reference numeral 5 denotes a blower connected to the diffuser 4, which is a driving unit for the diffuser 4. The wastewater is biologically treated in a wastewater treatment tank 2.

When air is blown out from the air diffuser 4 while introducing the wastewater 1 into the wastewater treatment tank 2, oxygen is supplied to the mixed liquid in the wastewater treatment tank 2, and the mixed liquid in the wastewater treatment tank 2 is raised by the rising bubble flow at this time. A circulating flow is generated in the processing tank. With this circulating flow,
In the process of the acetalized PVA hydrogel 3 flowing in the wastewater treatment tank 2, microorganisms that decompose and remove organic substances are attached to and bound to the hydrogel 3. Therefore, as a result of sufficient contact between the microorganisms and the organic matter, the organic matter in the mixed solution is decomposed and removed extremely efficiently and at a high speed. In addition, the microorganisms immobilized inside the carrier hardly peel off when the acetalized PVA hydrogel 3 flows in the mixed solution. Various screens or the like may be appropriately provided in the treatment tank in order to prevent the acetalized PVA-based hydrogel from overflowing.

The biologically treated water is sent to the final sedimentation tank 6 where the sediment is removed from the sludge discharge pipe 8,
The supernatant water 7 is discharged. The wastewater treatment tank used in the wastewater treatment apparatus of the present invention can increase the efficiency of wastewater treatment by using an acetalized PVA-based hydrogel. The use of gel can dramatically increase the wastewater treatment effect.

FIG. 7 is a flow chart showing another embodiment of the present invention in which a denitrification tank and a nitrification tank are arranged in this order from the water introduction side. 9 is a denitrification tank, and 12 is a nitrification tank. Drainage 1
Is supplied to the denitrification tank 9, the wastewater 1 is biologically denitrified by microorganisms in the denitrification tank under anaerobic conditions (anoxic conditions), and sent to the nitrification tank 12 as denitrification treatment water 11. The denitrification treatment water sent to the nitrification tank 12 is biologically nitrified by microorganisms in the nitrification tank under aerobic conditions. Part of the nitrification water 13 is circulated and returned to the denitrification tank 9 by the nitrification water return line 14, and the remaining nitrification water is sent to the final sedimentation tank 6, where the sediment is removed and the supernatant water 7 is removed.
Released as The rate of returning the nitrified water 13 to the denitrification tank 9 is about 1 to 5 times the supernatant water. The generated sludge is drawn out of the system by the sludge discharge pipe 8.

A stirring device 10 is provided in the denitrification tank 9, and a spherical acetalized PVA hydrogel 3 is charged into a mixed solution containing microorganisms in the denitrification tank 9. An organic carbon source is supplied to the denitrification tank as needed. Nitrification tank 12
An air diffuser 4 for supplying a gas such as air containing oxygen is connected to the blower 5 at the bottom of the inside, and is installed.
The same spherical acetalized PVA hydrogel 3 used in the denitrification tank is charged into the mixed liquid containing the microorganisms in the nitrification tank 12. The acetalized PVA-based hydrogel may be used by charging both the denitrification tank and the nitrification tank, or may be used by charging either one of them. However, it is more efficient to use it by charging both. Usually, it is used by charging both tanks. Different types of acetalized PVA may be charged into each tank.

In this apparatus, when the stirrer 10 is operated in a state where the denitrification treatment water 11 flows out to the nitrification tank 12 while introducing the wastewater 1 into the denitrification tank 9, Is generated, and this circulation stream causes acetalized PVA.
The hydrogel 3 flows in the denitrification tank 9, during which the microorganisms mainly composed of denitrifying bacteria present in the mixed solution adhere to and bind to the hydrogel 3. The mixed solution in the tank is denitrified by the immobilized denitrifying bacteria and floating denitrifying bacteria. The organic matter in the mixed solution is used as a respiratory substrate for denitrifying bacteria or a carbon source for cell synthesis. However, as described above, a carbon source may be added from outside the system as needed.

In the nitrification tank 12, the denitrification water 11 is supplied from the denitrification tank 9, and the nitrification water 1 in the nitrification tank 12 is supplied.
When air is blown out from the air diffuser 4 in a state where 3 flows out,
Oxygen is supplied to the mixed solution in the nitrification tank 12, and at the same time, while the circulating flow of the mixed solution is generated by the rising bubble flow, microorganisms mainly composed of nitrifying bacteria present in the mixed solution are acetalized PVA-containing water. It is attached and fixed to the gel 3. The liquid mixture in the tank is biologically nitrified by the immobilized nitrifying bacteria and the suspended nitrifying bacteria.

As a result, the microorganisms adhere and bind to and immobilize on the surface and / or inside the acetalized PVA hydrogel 3, whereby the component to be treated and the microorganisms come into sufficient contact. In addition, the microorganisms immobilized inside the carrier hardly peel off when the acetalized PVA hydrogel 3 flows in each tank. As a result, nitrogen in the water to be treated is decomposed and removed very efficiently and at a high speed. It is a matter of course that a screen or the like may be provided in the denitrification tank and / or the nitrification tank in order to prevent the hydrogel from overflowing out of the tank.

FIG. 8 is another flowchart of the present invention in which a nitrification tank and a denitrification tank are arranged in this order from the drain introduction side. The wastewater 1 is biologically nitrified by microorganisms in a nitrification tank under aerobic conditions, and then the nitrified water 13 is biologically denitrified by microorganisms in a denitrification tank under anaerobic conditions. The denitrification treatment water 11 is sent to the final sedimentation tank 6 and is discharged as supernatant water 7 after removing the sediment. The generated sludge is drawn out of the system by the sludge discharge pipe 8. Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

[0064]

EXAMPLES Gel Structure SEM photographs of the gel surface and a cross section cut at the center of the gel were taken to observe the microporosity of the outer layer surface and the structure of the inner layer.

Acetalization degree (%) A 0.2 g sample of the acetal-treated PVA hydrogel dried at 105 ° C. for 2 hours was precisely weighed and placed in a distillation apparatus charged with a 25% sulfuric acid solution. Next, the mixture is heated while sending steam, and the liberated formalin is distilled off together with water, and 2% N
a Absorbed in aqueous HSO ₃ solution. Excess NaHSO ₃ is converted to I ₂
The amount of free formalin was determined by back titration according to, and the degree of acetalization was calculated from the ratio (molar ratio) of the amount of free formalin to the amount of hydroxyl groups in the PVA gel.

Water content (%) After immersing the water-containing gel in water at 25 ° C. for 24 hours, the wet weight (W 1) of the gel from which water adhering to the surface was removed was measured and then dried at 105 ° C. for 4 hours. Thereafter, the dry weight (W2) of the gel was measured and calculated by the following equation. Water content (%) = (W1 -W2) / W1 × 100

TOC removal rate (mg-TOC / liter-gel · h) Since a gel having a higher microbial habitability has a higher TOC removal rate, the TOC removal rate was measured as an index of the microbial habitability. Specifically, 500 g of the hydrated gel was
After immersing for one month in a wastewater treatment tank at the Kuraray Okayama Plant, 100
g was taken out, put into 1 liter of drainage adjusted to TOC5OOmg / liter, and aerated, and T
The OC removal rate was determined.

Volume retention (%) The PVA-based hydrogel was found to have an apparent volume (volume in water) of 10%.
0 ml was collected, put into a 2 liter tall beaker (113 mm in diameter, 250 mm in height) with # 80 sandpaper adhered to the inner wall, and added with pure water to make 1 liter.
When a stirrer having a stainless steel stirring blade shown in FIG. 9 was set and stirred at 20 ° C. and 300 rpm,
The ratio of the volume of the hydrogel to the initially charged hydrogel, excluding the portion worn by the stirring for 14 days from the hydrogel initially charged.

Example 1 5% by weight of PVA (average degree of polymerization: 4,000, degree of saponification: 99.5 mol%), 1% by weight of sodium alginate ("Duck Algin NSPL" manufactured by Kibun Food Chemifa), 0.25% of sodium hydrogen carbonate A mixed aqueous solution of 70% by weight was prepared at 70 ° C. The mixed aqueous solution was phase-separated in suspension and was cloudy. The phase-separated liquid was fed at a rate of 5 ml / min using a roller pump equipped with a silicon tube having an inner diameter of about 5 mm and having a nozzle having an inner diameter of 4 mm at the tip, and stirred at a concentration of 0.1 mol / min with a stirrer. It was added dropwise to 1 liter of an aqueous solution of calcium chloride at 22 ° C. At least the sodium alginate on the surface solidified and settled in the aqueous solution of calcium chloride. The obtained solid was spherical.

This spherical solid was converted to formaldehyde 20
By immersing in an aqueous solution containing g / liter, sulfuric acid 200 g / liter, and sodium sulfate 100 g / liter at 40 ° C. for 210 minutes, it was coagulated and gelled, and was simultaneously subjected to acetalization. The obtained acetalized gel was washed with water to produce a highly flexible spherical hydrogel having a diameter of 3.8 mm.

When the obtained hydrogel was freeze-dried and the surface of the gel was observed with a 50.3 × SEM, crevasse-like microporosity was observed on the surface as shown in FIG. 1 or FIG. Were present in a square having a side of 500 μm.
When the aperture ratio was determined by image analysis, it was 2.3%. When the pore diameter inside the gel was measured by a mercury intrusion method, it was less than 15 μm, and the pore distribution showed a maximum at 8 μm. Further, the gel was cut at the center, and the cross section was observed with an SEM photograph. As a result, the gel had a three-dimensional network structure as shown in FIG. The thickness of the inner layer was about 99% / maximum diameter of the gel, and the thickness of the outer layer was about 1% / maximum diameter of the gel.

Next, in order to confirm the durability and microbial habitability of the hydrogel, a measurement of the volume retention rate and a nitrification test of ammonia were performed. The measurement of the volume retention was performed in accordance with the measurement of the volume retention described above. In the nitrification test, the hydrous gel which had been seeded with nitrifying sludge for one week was subjected to an ammonia concentration of 5%.
The rats were continuously acclimated at 0 mg / l and evaluated based on the rise in nitrification rate, and the habitability of microorganisms was examined. Table 1 shows the results.

COMPARATIVE EXAMPLE 1 A mixed aqueous solution of 5% by weight of PVA (average degree of polymerization: 4000, saponification degree: 99.5 mol%), 1% by weight of sodium alginate and 0.25% by weight of sodium hydrogen carbonate (phase separation into suspension) In the same manner as in Example 1 except that the acetalization time was set to 60 minutes, and a spherical structure having a diameter of 4.3 mm having a mesh layer structure formed by intertwining fibrous materials as a surface layer. Was obtained. The obtained hydrogel was freeze-dried, and the surface of the gel was observed with a SEM in the same manner as in Example 1. As a result, the surface as shown in FIG.
A net-like structure formed by entanglement of the fibrous materials was observed. Table 1 shows the evaluation results of the gel.

Example 2 5% by weight of PVA (average degree of polymerization: 3300, degree of saponification: 99.5% by mole), 1% by weight of sodium alginate ("Duck Algin NSPL" manufactured by Kibun Food Chemifa), 0.25% by weight of sodium sulfate % Mixed aqueous solution was prepared. The mixed aqueous solution was phase-separated in suspension and was cloudy. In the same manner as in Example 1, a highly flexible spherical hydrogel having a diameter of 3.8 mm was produced. Table 1 shows the results.

Comparative Example 2 Same as Example 1 except that a mixed aqueous solution of 5% by weight of PVA (average degree of polymerization 4000, saponification degree 99.5 mol%) and 1% by weight of sodium alginate was used instead of the phase separation liquid. A hydrogel having a diameter of 3.9 mm was produced. The obtained gel had a smooth surface because no phase separation liquid was used. Table 1 shows the evaluation results.

Comparative Example 3 A mixed aqueous solution of 7% by weight of PVA (average degree of polymerization: 2400, saponification degree: 99.8% by mole), 1% by weight of sodium alginate and 0.3% by weight of sodium hydrogen carbonate (phase separation into suspension) Example 1 except that turbidity was produced and used.
In the same manner as in the above, a spherical hydrogel having a diameter of 3.7 mm was obtained. Table 1 shows the evaluation results.

Example 3 A mixed aqueous solution of 3.7% by weight of PVA (average degree of polymerization: 8000, degree of saponification: 99.3% by mole), 1% by weight of sodium alginate and 0.3% by weight of sodium sulfate (phase in suspension) Example 1 except that white turbidity was prepared and used.
In the same manner as in the above, a spherical hydrogel having a diameter of 3.6 mm was obtained.
Table 1 shows the evaluation results.

[0078]

[Table 1]

Example 4 The acetalized P prepared in Example 1 was placed in a 1 m ³ aerobic tank.
VA water-containing gel was charged at 20% by volume, and a wastewater treatment apparatus as shown in FIG. 6 was configured by combining with a final settling tank of 0.6 m ³ . BOD 2500 mg / L (L) wastewater was supplied to the aerobic tank at 1 m ³ / day and treated continuously for 6 months. The BOD of the treated water was 200-300 mg / L, S
S was stable at 20 to 30 mg / L.

[0080] Example 5 0.2 m ³ and that used in Example 4 to nitrification denitrification tank and 0.2 m ³ of the same PVA hydrogel was charged 20% by volume, and a final sedimentation tank of 0.6 m ³ A wastewater treatment device as shown in FIG. 7 was configured in combination. BOD 200mg /
L, wastewater with a total nitrogen of 50 mg / L was supplied to the denitrification tank at 1.3 m ³ / day, and the nitrification-treated water was returned to the denitrification tank at a flow rate three times as high as that of the supernatant water. Jesui B
The OD was stable at 8 to 10 mg / L, and the SS was stable at 10 to 15 mg / L.

Example 6 A nitrification tank, a denitrification tank, and a final sedimentation tank were arranged in this order from the wastewater introduction side to constitute a wastewater treatment apparatus as shown in FIG. When 200 mg / L total nitrogen wastewater was supplied to the nitrification tank at a rate of 0.4 m ³ / day and treated continuously for one year, the total nitrogen of the treated water was 10 to 15 mg / L and SS was 10 to 20 mg / L.
mg / L.

Example 7 One liter of the carrier obtained in Example 2 was placed in a 10 L aeration tank and aerated, and TOC 100 ppm wastewater was continuously introduced at a rate of 42 mL / min. A wire mesh having an aperture of 2 mm was attached to the outlet of the aeration tank to prevent the carrier from flowing out. The TOC of the treated water after lapse of 10 days was 8.6 ppm and 7.5 ppm, respectively, indicating that sufficient treatment was performed. After that, the carrier was taken out, placed in a 20 L closed container, and further charged with 5 L of water.
In the gas phase of this vessel, 1 air containing 10 ppm of hydrogen sulfide was added.
After flowing at 0 L / min, the ventilation was stopped after 5 minutes and the container was sealed. Fifteen
After standing for one minute, the gas phase was collected with a microsyringe and analyzed by gas chromatography. The hydrogen sulfide concentration was below the detection limit.

[0083]

According to the present invention, it is possible to obtain a PVA-based hydrogel comprising an outer layer having a crevice-like microporous surface and an inner layer having a dense three-dimensional network structure. Such a hydrogel is excellent in the ability to capture microorganisms and inhabit the microorganisms, and is also excellent in durability such as abrasion resistance and mechanical strength, so it is preferable for wastewater treatment used under severe conditions such as vigorous stirring and deep tanks. Applied. Further, it is suitable as a filter medium, a packing material for chromatography, a cold insulator, a water retaining material, a carrier for a bioreactor, and the like.

[Brief description of the drawings]

FIG. 1 is a 50.3 × SEM photograph showing an example of the surface of a PVA-based hydrogel of the present invention.

FIG. 2 is a 458 × SEM photograph showing one example of the surface of the PVA-based hydrogel of the present invention.

FIG. 3 shows the results of measuring the pore size of the PVA-based hydrogel of the present invention by a mercury intrusion method.

FIG. 4 is a 50.3 × SEM photograph showing an example of a cross section of the PVA-based hydrogel of the present invention.

FIG. 5 shows the surface of the PVA-based hydrogel of Comparative Example 1.
It is a 0.3 times SEM photograph.

FIG. 6 is a flowchart illustrating an example of a wastewater treatment apparatus according to the present invention.

FIG. 7 is an example in which the wastewater treatment tanks of the wastewater treatment apparatus of the present invention are arranged in the order of a denitrification tank and a nitrification tank from the wastewater introduction side.

FIG. 8 is an example in which the wastewater treatment tanks of the wastewater treatment apparatus of the present invention are arranged in the order of a nitrification tank and a denitrification tank from the wastewater introduction side.

FIG. 9 is a stirring blade attached to a stirrer used to measure the volume retention of the PVA-based hydrogel of the present invention.

[Explanation of symbols]

 Reference Signs List 1 drainage 2 wastewater treatment tank 3 acetalized PVA-based hydrogel 4 diffuser 5 blower 6 final sedimentation tank 7 supernatant water 8 sludge discharge pipe 9 denitrification tank nitrification treatment water 10 stirrer 11 denitrification treatment water 12 nitrification tank 13 nitrification treatment Water 14 Nitrified water return line

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 29/04 C08L 29/04 G C12M 1/00 C12M 1/00 H C12N 1/00 C12N 1/00 S 11/08 11/08 B // C08J 3/12 CEP C08J 3/12 CEPZ C08L 29:04 C08L 29:04 (72) Inventor Takanori Kitamura 1-2-1, Kaigandori, Okayama City, Okayama Prefecture Kuraray Co., Ltd.

Claims (13)

[Claims] 1. A polyvinyl alcohol-based hydrogel comprising an outer layer having a crevasse-like microporous surface and an inner layer having a dense three-dimensional network structure. 2. The polyvinyl alcohol-based hydrogel according to claim 1, wherein the pore size of the micropores of the hydrogel is less than 20 μm as measured by a mercury intrusion method. 3. The polyvinyl alcohol-based hydrogel according to claim 1, wherein the hydrogel is a carrier for immobilizing microorganisms. 4. The polyvinyl alcohol-based hydrogel according to claim 1, wherein the hydrogel is a biocatalyst in which microorganisms are immobilized. 5. The polyvinyl alcohol-based hydrogel according to claim 1, wherein the hydrogel has a spherical shape with a diameter of 1 to 10 mm. 6. The polyvinyl alcohol-based hydrogel according to claim 1, wherein the volume retention after 14 days is 50% or more. 7. A polyvinyl alcohol molded product obtained by removing at least a part of water contained in the hydrogel according to any one of claims 1 to 6. 8. A polymer solution containing a vinyl alcohol-based polymer (A polymer) having a degree of polymerization of 3000 or more and a polymer (B polymer) which gels upon contact with a cation, can be subjected to phase separation. Substance (Substance C)
To prepare a phase-separated liquid, and contacting the phase-separated liquid with a cation-containing liquid to solidify at least the B polymer on the surface of the phase-separated liquid. The gel is brought into contact with a coagulating liquid having a solidifying ability to be gelled, and at the same time as the gelation and / or the acetalization after the gelation, the acetalization treatment is performed for a time longer than the time at which the degree of acetalization of 50% or more is obtained. A method for producing a polyvinyl alcohol-based hydrogel to be applied. 9. The method for producing a polyvinyl alcohol-based hydrogel according to claim 8, wherein part or all of the B polymer is removed after the acetalization treatment. 10. The method for producing a gel according to claim 8, wherein the polymer (B polymer) which gels upon contact with a cation is sodium alginate. 11. A wastewater treatment device comprising at least a wastewater treatment tank into which biocatalyst particles immobilized with microorganisms are charged and organic matter and / or inorganic matter in wastewater is decomposed and removed, wherein a carrier for immobilizing microorganisms is provided. A wastewater treatment device that is a polyvinyl alcohol-based hydrogel that is composed of an outer layer having a crevice-shaped microporous surface on the surface and an inner layer having a dense three-dimensional network structure. 12. A wastewater treatment tank into which a biocatalyst in which denitrifying bacteria are immobilized is charged and brought into contact with wastewater under anaerobic conditions, and a carrier gas in which nitrifying bacteria are immobilized is charged in aerobic conditions. A nitrification tank to be brought into contact with the wastewater underneath, these wastewater treatment tanks are arranged in this order from the introduction side of the wastewater, and a part of the nitrification treatment water flowing out of the nitrification tank is returned and circulated to the denitrification tank. The wastewater treatment apparatus according to claim 11, wherein the wastewater treatment apparatus is configured as follows. 13. A wastewater treatment tank into which a biocatalyst in which nitrifying bacteria are immobilized is charged and brought into contact with wastewater under aerobic conditions, and an anaerobic condition in which a biocatalyst in which denitrifying bacteria are immobilized is charged. 12. The wastewater treatment device according to claim 11, wherein the wastewater treatment device is a denitrification tank that is brought into contact with wastewater below, and the wastewater treatment tanks are arranged in this order from a wastewater introduction side.