JP2021195418A - Porous hydrous gel molded article, method of producing the same, and application of the same - Google Patents

Abstract

To provide a porous hydrous gel molded article capable of diminishing a dead space without miniaturizing the carrier when using a molded article as a microorganism carrier.SOLUTION: A porous hydrous gel molded article includes acetalized polyvinyl alcohol, where the molded article has continuous pores having a diameter of 0.1-50 μm from the surface to the inside, the aspect ratio A1 defined by the following formula (1) is 1-5, and the aspect ratio A2 defined by the following formula (2) is 2-10. A1=a/b (1), and A2=a/c (2), where a is a major axis when observing from a vertical direction by placing the molded article on the horizontal plane, b is a minor axis when observing from a vertical direction by placing the molded article on the horizontal plane, and c is a minor axis when observing from a horizontal direction by placing the molded article on the horizontal plane.SELECTED DRAWING: None

Description

The present invention relates to a porous hydrogel molded product containing a polymer. The present invention also relates to a method and application for producing such a porous hydrogel molded product.

Hydrous-containing gel molded products made of polymer materials are being actively researched as carriers for biocatalysts, water-retaining agents, cold-retaining agents, alternatives to biological gels such as eyes, skin, and joints, and sustained-release agents for drugs. Examples of the polymer material used as a raw material for these hydrogel molded products include agar, alginate, carrageenan, polyacrylamide, polyvinyl alcohol (hereinafter, may be abbreviated as PVA), and a photocurable resin. The carrier used for water treatment, particularly wastewater treatment, is required to have a high water content, excellent permeability of oxygen and a substrate, and high affinity as a living body. PVA is particularly excellent as a material satisfying these conditions.

In the water treatment method using a hydrogel molded product made of PVA, the hydrogel molded product is put into a treatment tank, and organic substances and the like in the treated water are decomposed by the action of microorganisms immobilized on the hydrogel molded product. It is a thing.

The challenge for microbial carriers is how to improve their ability to carry microbial carriers. If the capacity is low, a large amount of carrier must be charged into the treatment tank in order to ensure the desired processability. In addition, the stirring power and the amount of aeration for sufficiently stirring the carrier are increased, and the initial cost and the running cost are also increased.

Microorganisms adhere to the surface of the carrier, but the microbial membrane on the surface of the carrier is detached due to the flow in the tank or contact with a stirrer, and it is difficult to stably retain the microorganisms. In order to stably secure the ability to carry microorganisms, it is most efficient to improve the ability to carry microorganisms in the carrier. From the viewpoint of increasing the habitat area of microorganisms, it is preferable that the carrier charged into the treatment tank has continuous pores, that is, communication pores from the surface of the carrier to the center.

In a carrier having communication holes, most of the substrate such as nutrients and oxygen is consumed near the surface layer of the carrier by the bacteria adhering to the carrier, and cannot diffuse to the center of the carrier. Therefore, even if the carrier has communication holes, microorganisms that contribute to water treatment exist only in the region of several hundred μm from the surface layer of the carrier, and the region closer to the center is not suitable for water treatment. It becomes an active area, the so-called dead space.

Patent Document 1 describes a tubular microbial-immobilized carrier made of a thermoplastic resin, in which a plurality of protrusions are provided on the outer peripheral portion of the carrier, and the width of the tip portion of the protrusion is set to the tip portion of the adjacent protrusions. Microbial-immobilized carriers with an interval of 0.8 times or more are described. In this carrier, useful bacteria such as bacteria adhere only to the surface of the carrier, but since protozoa and metazoans that prey on them also coexist on the surface of the carrier, the occupancy rate of the useful bacteria could not be kept high. Further, when the carrier is used for a long period of time, there is a problem that the carriers collide with each other or the carriers collide with the wall surface of the treatment tank, the carriers are worn, and the biofilm is detached. For high-concentration wastewater, it is necessary to add a relatively large amount of carrier to increase the filling rate of the carrier, but in order to ensure sufficient fluidity of the carrier, a larger amount of stirring power and aeration amount should be secured. There was also a problem that the running cost was increased.

Patent Document 2 describes a polyvinyl alcohol-based gel molded product having a particle size of 1 to 20 mm and an acetalization degree of 1 to 20 mol%, which is obtained by contacting a polyvinyl alcohol and dialdehyde-containing liquid with an acid having a pH of 3 or less. Has been described. Since this molded product does not have holes, there is a problem that the habitat area of microorganisms is limited to only the surface of the molded product.

Patent Document 3 describes a hydrogel molded product made of polyvinyl acetal. Further, Patent Document 4 describes a porous water-containing gel molded product containing polyvinyl alcohol acetalized with dialdehyde; the degree of acetalization is 1 to 15 mol%, and the water content is 90 to 98% by weight. The pore size is 0.1 to 50 μm, and the amount of polyvinyl alcohol eluted from the porous hydrous gel molded product is 1 g or less per 1 kg of the porous hydrous gel molded product. Hydrous gel moldings are described.

Since the molded products described in Patent Documents 3 and 4 have continuous pores, it is said that microorganisms can be stably supported in the carrier. It is also said to be a carrier with good productivity. However, since the shapes of the molded products are all spherical, there is a problem that the region where microorganisms can live in the carrier is limited, especially under aerobic conditions for supplying oxygen. To solve this problem, the molded product can be atomized, but if it is atomized, the carrier may pass through the screen or mesh and flow out to the subsequent tank, or the screen or mesh may be blocked in the water treatment plant. There was a problem of getting rid of it.

Japanese Unexamined Patent Publication No. 2003-117757 Japanese Unexamined Patent Publication No. 2010-116439 Japanese Unexamined Patent Publication No. 7-41516 Japanese Unexamined Patent Publication No. 2015-10215

The present invention has been made to solve the above problems, and provides a porous hydrogel molded product capable of reducing dead space without atomizing the carrier when the molded product is used as a microbial carrier. The purpose is to do that. Another object of the present invention is to provide a carrier in which microorganisms are supported on a molded product, and a water treatment method for treating water by the microorganisms supported on the carrier.

The subject is a porous hydrogel molded product containing acetalized polyvinyl alcohol; the molded product has continuous pores with a diameter of 0.1 to 50 μm from its surface to the inside, and has the following formula ( To provide a molded product having _{an aspect ratio A 1} defined in 1) of _{1 to 5 and an aspect ratio A 2} defined in the following formula (2) of 2 to 10. Will be resolved by.

A ₁ = a / b (1)
A ₂ = a / c (2)
a: Major axis when the molded product is placed on the horizontal plane and viewed from the vertical direction b: Small diameter when the molded product is placed on the horizontal plane and viewed from the vertical direction c: When the molded product is placed on the horizontal plane and viewed from the horizontal direction Short diameter

At this time, it is preferable that the polyvinyl alcohol is acetalized with monoaldehyde or dialdehyde, and the degree of acetalization with monoaldehyde is 30 to 60 mol% or the degree of acetalization with dialdehyde is 1 to 10 mol%.

A carrier made by supporting a microorganism on the molded product is a preferred embodiment of the present invention. A water treatment method for treating water with microorganisms carried on this carrier is also a preferred embodiment of the present invention.

The subject is the method for producing the molded product; an aqueous solution containing polyvinyl alcohol and a water-soluble polysaccharide is applied to a base material and brought into contact with a coagulating liquid containing a polyvalent metal salt to gel the molded product. It is also solved by providing a method for producing a molded product, which comprises a step 1 of obtaining and a step 2 of reacting the obtained molded product with aldehyde to acetalize polyvinyl alcohol in the molded product.

The subject is the method for producing the molded product; the step 1 of obtaining a molded product by dropping an aqueous solution containing polyvinyl alcohol and a water-soluble polysaccharide from a nozzle into a coagulating liquid containing a polyvalent metal salt and gelling the product. And the step 2 of reacting the obtained molded product with aldehyde to convert the polyvinyl alcohol in the molded product into acetal, the nozzle is installed at a high place, and the water surface of the coagulating liquid is formed from the tip of the nozzle. It is also solved by providing a method for manufacturing a molded product having a long distance to the part.

According to the present invention, when the molded product is used as a microbial carrier, the dead space can be reduced without atomizing the carrier. Further, it is possible to provide a carrier in which microorganisms are supported on a molded product, and a water treatment method for treating water by the microorganisms supported on the carrier. According to the water treatment method, the amount of pollutants and the amount of water in the water can be reduced, so that the load on the water treatment facility and the environment can be suppressed.

The present invention relates to a porous hydrogel molded product containing acetalized PVA. So far, the present inventors have produced a porous hydrogel-containing molded product containing acetalized PVA, and reported that this molded product is useful as a carrier for supporting microorganisms (Patent Document 4). Since this molded product has a high affinity with living organisms and has continuous pores, it carries a large amount of microorganisms.

However, in the microbial carrier, microorganisms that contribute to water treatment exist only in a region of several hundred μm from the surface to the center of the carrier, and the other regions are regions that do not contribute to water treatment, so-called dead spaces. As described above, it is possible to reduce the dead space by reducing the size of the carrier, but this causes a problem that the carrier passes through the screen or mesh of the treatment tank and flows out to the subsequent tank. On the other hand, if the opening of the screen or mesh is made small, there is a problem that the screen or mesh is blocked. As a result of diligent studies, the present inventors have invented a molded product capable of reducing dead space without atomization when the molded product is used as a microbial carrier.

The present invention is a porous hydrogel molded product containing acetalized PVA;
The molded product has continuous holes with a diameter of 0.1 to 50 μm from the surface to the inside thereof.
A molded product having _{an aspect ratio A 1} defined by the following formula (1) of _{1 to 5 and an aspect ratio A 2} defined by the following formula (2) of 2 to 10. be.
A ₁ = a / b (1)
A ₂ = a / c (2)
a: Major axis when the molded product is placed on the horizontal plane and viewed from the vertical direction b: Small diameter when the molded product is placed on the horizontal plane and viewed from the vertical direction c: When the molded product is placed on the horizontal plane and viewed from the horizontal direction Short diameter

The present invention relates to a porous hydrogel molded product containing acetalized PVA. It is important to use acetalized PVA from the viewpoint of affinity with microorganisms, the ability to increase the retention of microorganisms, and the ability to ensure durability in repeated use.

The acetalized PVA can be obtained by acetalizing PVA (raw material PVA) as a raw material with an aldehyde described later. By acetalizing with aldehyde, a crosslinked structure can be introduced and PVA can be insolubilized. The raw material PVA can be obtained by polymerizing a vinyl ester such as vinyl acetate to obtain a polyvinyl ester, and then saponifying the polyvinyl ester.

The average degree of polymerization of the raw material PVA or acetalized PVA is preferably 1000 or more, and more preferably 1500 or more, from the viewpoint of the strength of the molded product. The degree of saponification is preferably 95 mol% or more, more preferably 98 mol% or more, from the viewpoint of the strength of the molded product.

As the raw material PVA used for producing the porous water-containing gel molded product, non-modified PVA can be used, and various modified PVA may be used as long as the effects of the present invention are not impaired. For example, carboxyl group-containing monomers such as (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, and itaconic acid or salts thereof; acrylamide-2-methylpropanesulfonic acid sodium, allylsulfonic acid sodium, vinyl. Vinyl sulfonic acid group-containing monomer such as sodium sulfonic acid or a salt thereof; Cationic monomer such as quaternary ammonium salt-containing monomer such as (meth) acrylamide-propyl-trimethylammonium chloride; ethylene, propylene and the like α-olefin; (meth) acrylate: acrylamide, dimethylacrylamide, N-methylolacrylamide, N-vinyl-2-pyrrolidone and other amide group-containing monomers; alkyl vinyl ether; trimethoxyvinylsilane and other silyl group-containing monomers Monomer; hydroxyl group-containing monomer such as allyl alcohol, dimethyl allyl alcohol, isopropenyl alcohol; acetyl group-containing monomer such as allyl acetate dimethyl allyl acetate and isopropenyl allyl acetate; halogen-containing such as vinyl chloride and vinylidene chloride Monomer; Examples thereof include a copolymer with an aromatic monomer such as styrene. From the viewpoint of availability, a homopolymer of PVA is preferably used.

The acetalized PVA is obtained by acetalizing the raw material PVA. As a method of acetalization, a method of acetalizing using a monoaldehyde having one carbonyl group in the molecule such as formaldehyde, or a dialdehyde having two carbonyl groups in the molecule such as glutaaldehyde is used. The method of acetalization is preferable. At this time, examples of the monoaldehyde include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and the like. Examples of the dialdehyde include glyoxal, malonaldehyde, succinaldehyde, glutaaldehyde, adipaldehyde, malealdehyde, tartaraldehyde, citraldehyde, phthalaldehyde, isophthalaldehyde, terephthalaldehyde and the like. From the viewpoint of availability, formaldehyde or glutaraldehyde is preferably used.

When the raw material PVA is acetalized using monoaldehyde, the degree of acetalization of the obtained PVA is preferably 30 to 60 mol%. When the raw material PVA is acetalized using dialdehyde, the degree of acetalization of the obtained PVA is preferably 1 to 10 mol% because the insolubilization rate of the raw material PVA is high. If the degree of acetalization is less than the lower limit of the above range, the strength required for the molded product may not be obtained. When the degree of acetalization exceeds the upper limit of the above range, the volume may be reduced due to shrinkage, the communication holes may be blocked, and the habitat area of microorganisms may be reduced.

The water content of the porous water-containing gel molded product is preferably 83 to 97% by mass. If the water content is less than 83% by mass, the molded product may shrink and the volume may become smaller, and the pore diameter of the continuous hole may become smaller. The water content is more preferably 85% by mass or more. On the other hand, if the water content exceeds 97% by mass, the shape retention and strength of the molded product may decrease. The water content is more preferably 95% by mass or less. In the present invention, unlike a foam such as a sponge, a molded product containing acetalized PVA does not easily release water even if it is deformed by an external force, and can provide an environment suitable for bacterial habitat. can.

The molded product of the present invention has continuous holes having a diameter of 0.1 to 50 μm from the surface to the inside. The molded product has continuous pores having a diameter of 0.1 to 50 μm from the surface to the inside, so that many microorganisms can be supported. The continuous holes can be confirmed by observing the cross section of the molded product using an electron microscope.

The diameter of the hole in the present invention is the diameter of the hole of the freeze-dried product of the molded product. The freeze-dried product can be obtained by freezing the molded product in liquid nitrogen and then vacuum-drying it at −50 ° C. The pore diameter is the peak value of the pore diameter distribution measured by a mercury porosimeter. The peak value of the pore size distribution measured by the mercury porosimeter is 0.1 to 50 μm, which means that the logarithmic pore diameter frequency distribution curve with the pore diameter on the horizontal axis and the logarithmic differential pore volume on the vertical axis is the pore diameter of 0.1. It means having a peak in the range of ~ 50 μm. When the diameter is less than 0.1 μm, when the molded product is used as a microbial carrier, the habitat area of the microorganism is reduced. The diameter is preferably 0.2 μm or more. Further, from the viewpoint of mass transfer, the diameter is more preferably 0.5 μm or more. On the other hand, when the diameter exceeds 50 μm, when the molded product is used as a microbial carrier, protozoa and metazoans that prey on bacteria can freely enter the carrier, so that the microorganisms that contribute to water treatment in the carrier It is not preferable because it lowers the occupancy rate and reduces the water treatment capacity. The diameter is preferably 10 μm or less, and more preferably 5 μm or less.

In the present invention, it is important that the _{aspect ratio A 1} defined by the following formula (1) is _{1 to 5, and the aspect ratio A 2} defined by the following formula (2) is 2 to 10. be.
A ₁ = a / b (1)
A ₂ = a / c (2)
a: Major axis when the molded product is placed on the horizontal plane and viewed from the vertical direction b: Small diameter when the molded product is placed on the horizontal plane and viewed from the vertical direction c: When the molded product is placed on the horizontal plane and viewed from the horizontal direction Short diameter

Here, the dead space in each shape is illustrated below on the premise that the fungus is present in a region of about 200 μm from the surface layer of the carrier toward the center. The dead space when the shape of the molded product is spherical (A ₁ = 1.0, A ₂ = 1.1, a = 4.3 mm, b = 4.2 mm, c = 3.9 mm) of Comparative Example 1. By calculation, about 74% of the volume of the molded product is dead space. On the other hand, when the shape of the molded product is the flat shape of Example 1 (A ₁ = 1.1, A ₂ = 3.0, a = 5.1 mm, b = 4.6 mm, c = 1.7 mm). When the dead space is calculated, about 64% of the volume of the molded product is the dead space. By thus changing the aspect ratio A ₁ and A _2, when comparing the carrier to each other to be captured by the mesh comparable dimensions, it is possible to reduce the dead space in the carrier.

In the present invention, _{it is important that the aspect ratio A 1} is 1 to 5 and A ₂ is 1 to 10. When both the aspect ratios A ₁ and A ₂ are close to 1, the shape of the molded product is close to a true sphere and the dead space ratio is increased. On the other hand, _{if the values of the aspect ratios A 1} and A ₂ are both large, the shape of the molded product becomes close to a string shape or a rod shape, and when the molded product is used as a microbial carrier, the separability on the screen deteriorates. It may cause clogging.

Here, if the aspect ratio A ₁ is too large, it easily passes through the screen or the mesh. From this point of view, the aspect ratio A ₁ is preferably 4 or less, more preferably 3 or less, and even more preferably 2 or less. On the other hand, if the aspect ratio A ₂ is too small, the dead space ratio increases. From this point of view, the aspect ratio A ₂ is preferably 2 or more, and more preferably 3 or more. The aspect ratio A ₂ is preferably 9 or less, and more preferably 7 or less.

In the above formulas (1) and (2), a is preferably 3 to 20 mm. If a is less than 3 mm, the carrier may pass through the screen or mesh and flow out to the subsequent tank in the water treatment plant, or the fluidity may deteriorate. It is more preferable that a is 4 mm or more. On the other hand, if a exceeds 20 mm, the fluidity in the tank may deteriorate. a is preferably 15 mm or less.

The method for producing the porous hydrogel molded product of the present invention is not particularly limited, but in _{order to obtain a molded product having desired aspect ratios A 1} and A ₂ , an aqueous solution containing a raw material polymer is applied to a base material to form a flat shape. Or an aqueous solution containing a raw material polymer may be dropped from a nozzle to increase the dropping distance to obtain a flat shape.

The base material to which the raw material polymer is applied may be a resin base material such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylic resin, fluororesin, acrylonitrile-styrene resin, acrylonitrile-butadiene-styrene resin, methacrylic resin, and polyethylene terephthalate. It can be a metal such as stainless steel, iron, copper, aluminum, nickel or titanium. In particular, from the viewpoint of handleability and availability, a resin base material, particularly polypropylene and vinyl chloride, is preferable.

In order to obtain a flat shape, the nozzle may be installed at a high place, an aqueous solution containing a raw material polymer may be dropped from the tip of the nozzle, and the dropping distance may be lengthened to obtain a flat shape. The dropping distance cannot be unequivocally determined because the appropriate range varies depending on the composition, viscosity, and temperature conditions of the raw material polymer, but an appropriate dropping distance is set from the viewpoint of the flatness and the variation in the shape of the molded product.

The shape of the molded product is not particularly limited as long as it satisfies the above aspect ratio A ₁ and A _2, flat, disc-shaped, ellipsoidal, shape such as contact lenses is uneven portions, such as a dome shape Can be mentioned.

In step 1, it is preferable to apply an aqueous solution containing PVA and a water-soluble polysaccharide to an aqueous solution containing a raw material polymer on a base material, bring it into contact with a coagulating solution containing a polyvalent metal salt, and gel it to obtain a molded product. .. At this time, the obtained molded product may be cut. Examples of the water-soluble polysaccharide include alkali metal salts of alginic acid, carrageenan, mannan, and chitosan. Sodium alginate is preferred from the standpoint of availability. Sodium alginate is a kind of polysaccharide mainly produced from brown algae (kelp and the like), and is formed from sodium salts of monosaccharides called α-L-gluronic acid and β-D-mannuronic acid having a carboxyl group.

The PVA concentration of the aqueous solution in step 1 is preferably 4 to 12% by mass. The higher the concentration of PVA, the stronger the gel is formed. However, if the required gel strength is obtained, the lower the concentration of PVA is advantageous in terms of raw material cost. The concentration of the water-soluble polysaccharide in the aqueous solution of Step 1 is preferably 0.2 to 3% by mass, more preferably 0.5 to 2% by mass, from the viewpoint of gel formability.

Examples of the cationic species of the polyvalent metal salt include alkaline earth metals such as calcium, magnesium, strontium and barium; aluminum, nickel ion and cerium. Among them, alkaline earth metals are preferable as the cationic species of the polyvalent metal salt. The concentration of the polyvalent metal salt in the coagulation liquid is preferably 0.03 to 0.5 mol / L.

The production method for obtaining a porous hydrogel molded product containing acetalized PVA is not particularly limited, but an aqueous solution containing PVA and water-soluble polysaccharide is brought into contact with a coagulating liquid containing a polyvalent metal salt to gel. It has a step of obtaining a molded product and a step of reacting the obtained molded product with an aldehyde to acetalize polyvinyl alcohol in the molded product.

Step 1 is as described above. Then, the molded product obtained in step 1 is brought into contact with the acetalization reaction liquid in step 2 to acetalize the PVA in the molded product. As the acetalization reaction progresses, phase separation is induced in the polyvinyl alcohol-rich region and the water-rich region, the polyvinyl alcohol-rich region becomes the skeleton portion of the gel molded product, and the water-rich region becomes continuous pores. A porous structure is formed inside.

In step 2, it is preferable that the obtained molded product is brought into contact with an acetalization reaction solution consisting of an aqueous solution having a pH of 3 or less and reacted with monoaldehyde or dialdehyde to acetalize the PVA in the molded product. Examples of the acid contained in the acetalization reaction solution include acids such as sulfuric acid, hydrochloric acid, phosphoric acid, nitrate, acetic acid and oxalic acid, and acid salts such as sodium hydrogensulfate and ammonium hydrogensulfate. Among them, sulfuric acid is preferable from the viewpoint of versatility and cost. When the acid concentration is low, the reaction time is long and the amount of PVA eluted from the molded product is large. When monoaldehyde is adopted, the pH of the acetalization reaction solution is preferably 1.0 or less, more preferably 0.6 or less. Further, when dialdehyde is adopted, the pH of the acetalization reaction solution is more preferably 2.5 or less, and further preferably 2 or less. In the case of dialdehyde, if the pH is too low, continuous pores may not be formed in the molded product or volume shrinkage may become significant. The pH of the acetalization reaction solution is preferably 1.0 or higher. The pH is usually 0 or higher.

It is also preferable that the acetalization reaction solution used in step 2 contains a metal salt. Examples of the metal salt at this time include sulfates, hydrochlorides, phosphates, nitrates, acetates, oxalates, tartrates and the like, and among them, sulfates and hydrochlorides are preferable. Further, examples of the cation species include alkali metals and alkaline earth metals. At this time, in the acetalization reaction solution, the value obtained by multiplying the concentration of the metal cation by the valence is preferably 0.1 to 5 mol / L. If the value obtained by multiplying the concentration of the metal cation by the valence is less than 0.1 mol / L, the porous structure may not be formed in the molded product or the amount of PVA eluted in the reaction solution may increase. It is more preferably 2 mol / L or more. On the other hand, if the value obtained by multiplying the concentration of the metal cation by the valence exceeds 5 mol / L, scale may occur, and it is more preferably 3 mol / L or less.

Here, the value obtained by multiplying the concentration of the metal cation by the valence is, for example, the value obtained by multiplying the concentration of sodium ion by 1 when the _{metal salt contained in the acetalization reaction solution is sodium sulfate (Na 2} SO _4). That is. Therefore, when the concentration of sodium sulfate is 1 mol / L, the value is 2 mol / L. When the metal salt is sodium chloride (NaCl), it is the value obtained by multiplying the concentration of sodium ions by 1. Therefore, when the concentration of sodium chloride is 1 mol / L, the value is 1 mol / L. When the metal salt is magnesium sulfate (ו ₄ ), it is the value obtained by multiplying the concentration of magnesium ions by 2. Therefore, when the concentration of magnesium sulfate is 1 mol / L, the value is 2 mol / L.

The temperature of the acetalization reaction solution when the molded product is brought into contact with the acetalization reaction solution is preferably 20 to 80 ° C. If the temperature is lower than 20 ° C., the reaction time becomes long, so that PVA and aldehyde may be eluted in the acetalization reaction solution. Further, if the temperature exceeds 80 ° C., corrosion due to acid in the plant is severe, which is not preferable.

In the above production method, when producing a molded product having continuous pores having a large diameter, cornstarch, tapioca starch, potato starch, various modified starches and the like are added to the aqueous solution in step 1 as needed, and step 2 is performed. In the above, it is also possible to raise the temperature at which the molded product is brought into contact with the acetalization reaction liquid to the gelatinization temperature or higher and gelatinize the molded product to promote phase separation and produce a molded product having continuous holes having a large diameter. ..

The order of steps 1 and 2 is not particularly limited. The step of gelling to obtain particles and the step of acetalizing may be performed at the same time. It may be gelled to obtain particles and then acetalized. Further, it may be acetalized and then gelled. Above all, it is preferable to perform step 1 and step 2 in this order.

When acetalizing with monoaldehyde, the concentration of monoaldehyde in the acetalization reaction solution is preferably 0.01 to 1.5 mol / L with respect to the number of mols of all the monomer units in PVA. If the monoaldehyde concentration is less than 0.01 mol / L, the acetalization reaction does not proceed efficiently, and the elution of the raw material PVA from the obtained molded product may increase. The monoaldehyde concentration is more preferably 0.3 mol / L or more. On the other hand, if the monoaldehyde concentration exceeds 1.5 mol / L, the obtained molded product may become brittle, shrinkage in the manufacturing process may increase, and the water content may decrease. Further, when the molded product is used as a microbial carrier, the shrinkage of the molded product may reduce the habitatability of the microorganism. Therefore, when the wastewater is decomposed, the decomposition efficiency may decrease. The monoaldehyde concentration is more preferably 1.0 mol / L or less. By setting the monoaldehyde concentration in such a range, it is possible to obtain a molded product having excellent habitat of microorganisms.

When acetalizing with dialdehyde, the concentration of dialdehyde in the aqueous solution is preferably 0.001 to 0.02 mol / L with respect to the number of mols of all the monomer units in PVA. If the dialdehyde concentration is less than 0.001 mol / L, the acetalization reaction does not proceed efficiently, the cross-linking becomes insufficient, and the elution of PVA from the obtained molded product may increase. The dialdehyde concentration is more preferably 0.003 mol / L or more. On the other hand, when the dialdehyde concentration exceeds 0.02 mol / L, the obtained molded product becomes brittle, shrinkage in the manufacturing process becomes large, the water content decreases, and pores are too small or not formed. There is a risk of Further, when the molded product is used as a microbial carrier, the shrinkage of the molded product may reduce the habitatability of the microorganism. Therefore, when the wastewater is decomposed, the decomposition efficiency may decrease. The dialdehyde concentration is more preferably 0.015 mol / L or less. By setting the dialdehyde concentration in such a range, it is possible to obtain a molded product having excellent habitat of microorganisms.

The molded product of the present invention can also be used as a carrier for supporting microorganisms, a carrier for a biocatalyst, a water-retaining agent, a cold-retaining agent, a substitute for a biological gel such as eyes, skin and joints, and a sustained-release agent for a drug. Among them, a preferred embodiment of the present invention is a carrier in which a microorganism is carried on a molded product. It is also a preferred embodiment of the present invention to treat water containing a substance to be treated such as wastewater with a microorganism carried on the carrier. At this time, the microorganism supported on the carrier may be an anaerobic microorganism or an aerobic microorganism. The type of microorganism may be selected according to the stain and type of water to be treated.

The method of supporting the microorganism on the carrier is not particularly limited, and examples thereof include a method of mixing the carrier and activated sludge in the reaction vessel of the water treatment apparatus. By mixing the carrier and the activated sludge in this way, microorganisms such as bacteria contained in the activated sludge are supported on the carrier.

A method may be adopted in which the carrier is added to an aqueous solution containing microorganisms and nutritional components, and the carrier on which the microorganisms are supported in advance is added to the reaction vessel of the water treatment apparatus. However, even if such a method is not adopted, the carrier of the present invention is sufficiently supported with microorganisms. Therefore, a method of adding the carrier to the reaction tank of the water treatment apparatus in which the carrier already supported by the microorganism is present can be preferably adopted without carrying the microorganism on the carrier in advance.

The type of water to be treated is not particularly limited as long as it contains a substance that can be decomposed by microorganisms, but it is not particularly limited, but it is sewage discharged from toilets, miscellaneous wastewater discharged from cooking or washing, and factories. It is possible to exemplify industrial wastewater discharged from a business establishment or the like. The water to be treated may be muddy mainly composed of solid components or liquid mainly composed of dissolved components.

Since the microbial carrier of the present invention has a high processing capacity per carrier, the stirring power or aeration amount required for the input amount and flow of the carrier is reduced when operating the water treatment device, which leads to reduction of initial cost and running cost. be able to.

Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
Water was added to PVA (average polymerization degree 1700, saponification degree 99.8 mol%) so that PVA was 7% by mass, and treated in hot water for 50 minutes to dissolve PVA. Sodium alginate was added to this PVA aqueous solution so as to be 1% by mass, and the mixture was stirred and dissolved for 30 minutes to prepare a mixed aqueous solution. The upper surface of the mixed aqueous solution was released, and the mixed aqueous solution was dropped into a 6 mm × 5.7 mm rectangular acrylic container having a partition plate on the side surface with a dropper and placed up to a height of 3 mm. After allowing to stand for 10 minutes, the whole rectangular acrylic container was submerged in 1 L of a coagulation bath composed of a calcium chloride aqueous solution having a concentration of 0.3 mol / L. The mixed aqueous solution in the rectangular acrylic container was gelled flat in the calcium chloride aqueous solution.

This flat molded product was separated from the calcium chloride aqueous solution, taken out from the container, and then immersed in 1 L of the acetalization reaction solution at 40 ° C. for 60 minutes. Here, the acetalization reaction solution is an aqueous solution having a pH of 1.7 containing 0.012 mol / L of glutaraldehyde, 9 g / L of sulfuric acid, and 100 g / L of sodium sulfate. Then, the molded product was separated from the acetalization reaction solution and washed with water to obtain a flat water-containing gel molded product. The obtained molded product was allowed to stand on a horizontal plate. When observed from the horizontal direction, the shape of the molded product was rectangular and flat. When a, b, and c were measured according to the method described above and the aspect ratio A ₁ and the aspect ratio A ₂ were calculated, the aspect ratio A ₁ was 1.1 and the aspect ratio A ₂ was 3.0 (a = 5. 1 mm, b = 4.6 mm, c = 1.7 mm). When the surface and cross section of the obtained hydrogel molded product were observed by SEM, it was confirmed that continuous holes existed from the outer surface toward the center. It was confirmed that the hydrogel molded product of Example 1 had holes having a diameter of 3 μm. The degree of acetalization of PVA in this water-containing gel molded product was 2.0 mol%, and the water content was 93%. The results are shown in Table 1.

This hydrogel molded product was frozen in liquid nitrogen and then vacuum dried at −50 ° C. to obtain a freeze-dried sample. This sample was measured for pore distribution using an automatic mercury porosimeter pore distribution measuring device AutoPore V series manufactured by Shimadzu Science East Japan Co., Ltd., and the peak value is described as the pore diameter in this example and subsequent comparative examples.

Using the hydrogel molded product thus obtained, an ammonia nitrification test was conducted with an ammonia removal wastewater treatment device by nitrification. As the aeration tank, an aeration tank having a water tank volume of 1 liter was used, and a carrier (molded product) having a bulk volume of 100 mL, which was 10% by volume of the volume, was filled. Further, the sewage treatment sludge was put into the same tank so that the MLSS (Mixed Liquor Suspended Solid) was 4000 mg / L. For aeration, 3.5 L / min of air was supplied by a porous air diffuser, and the aeration was continuously operated at a water tank temperature in the range of 25 to 30 ° C. Continuously feeding ammonium chloride 270 mg / L, the simulated wastewater containing sodium bicarbonate 2800 mg / L from 400 ml / day, giving ammonia volumetric loading from 0.03kg / ^(m 3 · d) in that tank, tank sludge The volumetric load was gradually increased while flowing out, the treatability for 70 days was confirmed, and the upper limit of the amount of ammonia removed and the number of bacteria in the carrier at that time were measured.

The amount of ammonia removed [kg / m ³ · d] uses the ammonia concentration of raw water [mg / L], the ammonia concentration of treated water [mg / L], the drainage flow rate [L / day], and the tank volume [L]. It is calculated by the following formula.
Ammonia removal amount = (Ammonia concentration of raw water-Ammonia concentration of treated water) x Wastewater flow rate x 10 ^-9 / (Tank volume x 10 ^-3 )

The number of bacteria in the carrier was measured as follows. Several carriers were sampled, purified water was added and washed several times until there were no suspended matter. Sterilized water was added to the carrier, the carrier was crushed with a homogenizer, and the supernatant was collected. Using a Kikkoman Biochemifa Lumitester K-200, luminescence analysis of the supernatant was performed, and ATP (adenosine triphosphate) extracted from the supernatant was measured. The number of bacteria per unit volume of the carrier was measured from the weight of the measurement sample (mixture of carrier and sterile water) and the bulk specific gravity data of the carrier. The results of the ammonia nitrification test are shown in Table 2.

Example 2
Water was added to PVA (average polymerization degree 1700, saponification degree 99.8 mol%) so that PVA was 7% by mass, and treated in hot water for 50 minutes to dissolve PVA. Sodium alginate was added to this PVA aqueous solution so as to be 1% by mass, and the mixture was stirred and dissolved for 30 minutes to prepare a mixed aqueous solution. 100 g of this mixed aqueous solution is sent by a roller pump equipped with a silicon tube hose having an inner diameter of 3.2 mm with a nozzle having an inner diameter of 3 mm attached to the tip, and a calcium chloride aqueous solution having a concentration of 0.3 mol / L is stirred by a stirrer. The mixture was added dropwise to 1 L of a coagulation bath consisting of a dry zone of 25 cm. The dry zone is the distance between the nozzle and the liquid level of the coagulation bath, that is, the distance until the mixed aqueous solution lands on the coagulation bath. The dropped droplets gelled flat in the calcium chloride aqueous solution and settled.

This flat molded product was separated from the calcium chloride aqueous solution, taken out from the container, and then immersed in 1 L of the acetalization reaction solution at 40 ° C. for 90 minutes. Here, the acetalization reaction solution is an aqueous solution having a pH of 0.3 containing 1 mol / L of formaldehyde, 150 g / L of sulfuric acid, and 100 g / L of sodium sulfate. Then, the molded product was separated from the acetalization reaction solution and washed with water to obtain a flat water-containing gel molded product. The obtained molded product was allowed to stand on a horizontal plate. When observed from the horizontal direction, the shape of the molded product was dome-shaped. When a, b, and c were measured and the aspect ratio A ₁ and the aspect ratio A ₂ were calculated according to the above method, the aspect ratio A ₁ was 1.0 and the aspect ratio A ₂ was 3.3 (a = 5. 0 mm, b = 4.9 mm, c = 1.5 mm). When the surface and cross section of the obtained hydrogel molded product were observed by SEM, it was confirmed that continuous holes existed from the outer surface toward the center. It was confirmed that the hydrogel molded product of Example 2 had holes having a diameter of 4 μm. The degree of acetalization of PVA in this water-containing gel molded product was 48 mol%, and the water content was 87%. The results are shown in Table 1. Further, using the obtained molded product, an ammonia nitrification test by nitrification was carried out in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 1
Water was added to PVA (average polymerization degree 1700, saponification degree 99.8 mol%) so that PVA was 7% by mass, and treated in hot water for 50 minutes to dissolve PVA. Sodium alginate was added to this PVA aqueous solution so as to be 1% by mass, and the mixture was stirred and dissolved for 30 minutes to prepare a mixed aqueous solution. 100 g of this mixed aqueous solution is sent by a roller pump equipped with a silicon tube hose having an inner diameter of 3.2 mm with a nozzle having an inner diameter of 1.5 mm attached to the tip, and stirred with a stirrer to a concentration of 0.1 mol / L chloride. It was added dropwise to 1 L of a coagulation bath composed of an aqueous calcium solution. The dropped droplets gelled into a spherical shape in an aqueous calcium chloride solution and settled.

This spherical molded product was separated from an aqueous calcium chloride solution and immersed in 1 L of an acetalization reaction solution at 40 ° C. for 60 minutes. Here, the acetalization reaction solution is an aqueous solution having a pH of 1.7 containing 0.012 mol / L of glutaraldehyde, 10 g / L of sulfuric acid, and 120 g / L of sodium sulfate. Then, the molded product was separated from the acetalization reaction solution and washed with water. As a result, _{a spherical hydrogel molded product having an aspect ratio A 1} of 1.0 and an aspect ratio A ₂ of 1.1 (a = 4.3 mm, b = 4.2 mm, c = 3.9 mm) was obtained. Further, the hole diameter was measured in the same manner as in Example 1. The results are shown in Table 1. Further, using the obtained molded product, an ammonia nitrification test by nitrification was carried out in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 2
Water was added to PVA (average polymerization degree 1700, saponification degree 99.8 mol%) so that PVA was 7% by mass, and treated in hot water for 50 minutes to dissolve PVA. Sodium alginate was added to this PVA aqueous solution so as to be 1% by mass, and tapioca starch aqueous solution was added so as to be 5% by mass, and the mixture was stirred and dissolved for 30 minutes to prepare a mixed aqueous solution. 100 g of this mixed aqueous solution is sent by a roller pump having an inner diameter of 3.2 mm with a nozzle having an inner diameter of 4.0 mm attached to the tip and equipped with a silicon tube hose, and stirred with a stirrer to a concentration of 0.1 mol / L calcium chloride. It was added dropwise to 1 L of a coagulation bath made of an aqueous solution heated to 80 ° C. The dropped droplets were gelled into a spherical shape in an aqueous calcium chloride solution, and the starch in the gel was gelatinized and swollen, and settled in a colorless and translucent state.

This spherical molded product was separated from an aqueous calcium chloride solution and immersed in 1 L of an acetalization reaction solution at 80 ° C. for 15 minutes. Here, the acetalization reaction solution is an aqueous solution containing 100 g / L of formaldehyde and 150 g / L of sulfuric acid. Then, the molded product was separated from the acetalization reaction solution and washed with water. As a result, _{a spherical hydrogel molded product having an aspect ratio A 1} of 1.1 and an aspect ratio A ₂ of 1.1 (a = 4.2 mm, b = 4.0 mm, c = 4.0 mm) was obtained. Further, the hole diameter was measured in the same manner as in Example 1. The results are shown in Table 1. Further, using the obtained molded product, an ammonia nitrification test by nitrification was carried out in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 3
Water was added to PVA (average polymerization degree 1700, saponification degree 99.8 mol%) so that PVA was 7% by mass, and treated in hot water for 50 minutes to dissolve PVA. Sodium alginate was added to this PVA aqueous solution so as to be 1% by mass, and the mixture was stirred and dissolved for 30 minutes. Further, glutaraldehyde was added to this aqueous solution so as to be 10 mol% based on the mol number of all the monomer units in PVA, and then sufficiently mixed to prepare a mixed aqueous solution. 100 g of this mixed aqueous solution was sent from a calcium chloride aqueous solution having a concentration of 0.1 mol / L, which was sent by a roller pump having an inner diameter of 3.2 mm with a nozzle having an inner diameter of 1.5 mm attached to the tip and equipped with a silicon tube hose, and stirred with a stirrer. It was dropped into 1 L of the coagulation bath. The dropped droplets gelled into a spherical shape in an aqueous calcium chloride solution and settled.

This spherical molded product was separated from an aqueous calcium chloride solution and immersed in 1 L of an acetalization reaction solution at 40 ° C. for 60 minutes. Here, the acetalization reaction solution is an aqueous solution having a pH of 0.6 containing 0.025 mol / L, 100 g / L sulfuric acid, and 100 g / L sodium sulfate. Then, the molded product was separated from the acetalization reaction solution and washed with water. As a result, _{a spherical hydrogel molded product having an aspect ratio A 1} of 1.1 and an aspect ratio A ₂ of 1.1 (a = 3.3 mm, b = 3.1 mm, c = 3.0 mm) was obtained. When this molded product was observed by SEM, no holes were formed. The results are shown in Table 1. Further, using the obtained molded product, an ammonia nitrification test by nitrification was carried out in the same manner as in Example 1. The results are shown in Table 2.

As shown in Table 2, when Examples 1 and 2 and Comparative Example 1 are compared, the porous hydrogel molded product having a high aspect ratio has an improved number of bacteria held by the carrier and the upper limit of the amount of ammonia removed. The value has improved.

In the example in which the pore size is larger than the preferable range as in Comparative Example 2, the number of bacteria retained by the carrier is smaller than that of the carrier of the example having the pore size in the preferable range, and the upper limit of the amount of ammonia removed is also the example. The result was inferior to that of the carriers 1 and 2. In the state without continuous pores as in Comparative Example 3, the number of bacteria retained by the carrier was smaller than that of the other Examples and Comparative Examples, and the upper limit of the amount of ammonia removed was the smallest.

Claims (6)

A porous hydrogel molded product containing acetalized polyvinyl alcohol;
The molded product has continuous holes with a diameter of 0.1 to 50 μm from the surface to the inside thereof.
A molded product having _{an aspect ratio A 1} defined by the following formula (1) of _{1 to 5 and an aspect ratio A 2} defined by the following formula (2) of 2 to 10.
A ₁ = a / b (1)
A ₂ = a / c (2)
a: Major axis when the molded product is placed on the horizontal plane and viewed from the vertical direction b: Small diameter when the molded product is placed on the horizontal plane and viewed from the vertical direction c: When the molded product is placed on the horizontal plane and viewed from the horizontal direction Short diameter The molding according to claim 1, wherein the polyvinyl alcohol is acetalized with monoaldehyde or dialdehyde, and the degree of acetalization with monoaldehyde is 30 to 60 mol% or the degree of acetalization with dialdehyde is 1 to 10 mol%. thing. A carrier obtained by supporting a microorganism on the molded product according to claim 1 or 2. A water treatment method for treating water with a microorganism carried on the carrier according to claim 3. The method for producing a molded product according to claim 1 or 2.
Step 1 of applying an aqueous solution containing polyvinyl alcohol and a water-soluble polysaccharide to a substrate, contacting it with a coagulating liquid containing a polyvalent metal salt, and gelling it to obtain a molded product.
A method for producing a molded product, which comprises a step 2 of reacting the obtained molded product with an aldehyde to acetalize polyvinyl alcohol in the molded product. The method for producing a molded product according to claim 1 or 2.
Step 1 to obtain a molded product by dropping an aqueous solution containing polyvinyl alcohol and a water-soluble polysaccharide from a nozzle into a coagulating solution containing a polyvalent metal salt and gelling the solution.
It has a step 2 of reacting the obtained molded product with an aldehyde to acetalize the polyvinyl alcohol in the molded product.
A method for manufacturing a molded product in which the nozzle is installed at a high place and the distance from the tip of the nozzle to the water surface of the coagulating liquid is lengthened.