JP2023085581A - Molded product of porous hydrogel, production method thereof and use thereof - Google Patents

Abstract

To provide a molded product of porous hydrogel which has a good volume restoration property when dipped in water after storage in a reduced volume by compression, drying and the like.SOLUTION: Provided is a molded product of a porous hydrogel comprising polyvinyl alcohol acetalized with a monoaldehyde or a dialdehyde, where the degree of acetalization when acetalized with a monoaldehyde is 15-80 mol% or the degree of acetalization when acetalized with a dialdehyde is 0.1-15 mol%, the polyvinyl alcohol includes a monomer unit containing a carboxylic acid salt with the content of the monomer unit being 1-7 mol%, and the molded product (A) has continuous pores with a specific surface area of 2-15 m2/g.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to porous hydrogel moldings containing polyvinyl alcohol acetalized with monoaldehyde or dialdehyde. The present invention also relates to a method for producing such porous hydrogel moldings and uses thereof.

Hydrous gel moldings made of polymer materials have been extensively studied as biocatalyst carriers, water retention agents, cooling agents, substitutes for biogels for eyes, skin, joints, etc., and as base materials for sustained drug release agents. . Macromolecular materials used as raw materials for these hydrogel moldings include agar, alginate, carrageenan, polyacrylamide, polyvinyl alcohol (hereinafter sometimes abbreviated as PVA), photocurable resins, and the like. Carriers used for wastewater treatment are required to have a high water content, excellent permeability to oxygen and substrates, and high affinity with living organisms. PVA is particularly excellent as a material that satisfies these conditions.

The ability required in a PVA-containing hydrous gel molded article varies depending on the application. For example, in the case of agricultural water-retaining materials and artificial culture media, affinity for organisms and plants, water-retaining capacity such as water content, water discharge properties, handling properties such as being able to be transported in a reduced volume, light resistance, and the like can be mentioned.

Porous hydrogel moldings made of PVA are also used for wastewater treatment. In the wastewater treatment method using a porous hydrogel molded article made of PVA, the hydrogel molded article is put into a treatment tank, and the wastewater in the treatment tank is decomposed by the action of microorganisms supported in the hydrogel molded article. It is something to do.

The hydrous gel moldings used for biological treatment are first required to have a high affinity with living organisms, have continuous pores, and carry a large amount of microorganisms. In addition, after the volume of the water-containing gel molding is reduced by compression, drying, or the like, and stored, the volume recovery property is good when swollen with water. By having good volume restoring property, it is possible to transport the water-containing gel molding while reducing its volume. Therefore, it becomes unnecessary to enclose water together with the hydrous gel molding and transport it, so that the transportation cost can be reduced and the labor of putting the hydrous gel molding into the treatment tank can be simplified. When using a microbial carrier in a wastewater treatment plant, the amount of transport is from several tens of ^m3 to several hundreds of ^m3 in many cases. As well as improving efficiency, transportation costs can also be reduced.

Patent Literature 1 describes a method for producing a hydrous gel molded product made of polyvinyl acetal, characterized in that after molding a solution containing polyvinyl alcohol, the molded product is acetalized. The hydrous gel molded article obtained by this method is said to have high strength and excellent water resistance, and is useful for bioreactors, carriers for wastewater treatment, water retention materials, cold insulation materials, and the like.

Patent Document 2 discloses a porous hydrogel molding containing polyvinyl alcohol acetalized with dialdehyde; is 0.1 to 50 μm, and the amount of polyvinyl alcohol eluted from the porous hydrogel molded article is 1 g or less per 1 kg of the porous hydrogel molded article. Moldings are described. And, this porous hydrogel molding is said to be excellent in microbial habitability and agitation durability.

However, neither of the molded articles described in Patent Documents 1 and 2 has sufficient volume recovery when swollen with water after the volume of the molded article is reduced by compression, drying, etc. and stored. Therefore, it was difficult to store and transport the molded products described in Patent Documents 1 and 2 in a reduced volume state.

JP-A-7-41516 JP 2015-10215 A

The present invention has been made to solve the above-mentioned problems, and provides a porous hydrous gel molded article having good volume restoration property when immersed in water after being stored after being reduced in volume by squeezing, drying, or the like. It is intended to

The above object is a porous hydrogel molding (A) containing polyvinyl alcohol acetalized with monoaldehyde or dialdehyde; the degree of acetalization when acetalized with monoaldehyde is 15 to 80 mol%. Alternatively, the degree of acetalization when acetalized with a dialdehyde is 0.1 to 15 mol%, the polyvinyl alcohol contains a monomer unit containing a carboxylate, and the content of the monomer unit is 1 Solved by providing a porous hydrous gel molding (A), characterized in that the molding (A) has continuous pores and a specific surface area of 2 to 15 m ² /g. be done.

Particles having an equivalent spherical diameter of 2 to 10 mm are preferred.

At this time, the water content is preferably 90 to 98% by mass.

A preferred embodiment of the present invention is a microbial carrier comprising the shaped article (A).

The porous hydrogel molded product (A) is obtained by dropping an aqueous solution containing polyvinyl alcohol containing a monomer unit containing a carboxyl group or a derivative thereof and a water-soluble polysaccharide into an aqueous solution containing a polyvalent metal salt to form a gel. Step 1 of obtaining particles by allowing the obtained particles to have a pH of 3 or less, containing a metal salt, and having a value obtained by multiplying the cation concentration of the metal salt by a valence of 0.2 to 5 mol / L Step 2 of reacting with monoaldehyde or dialdehyde in addition to an aqueous solution to acetalize the polyvinyl alcohol in the particles, and Step 3 of contacting the particles obtained in Step 2 with an aqueous solution having a pH of 8 or higher. provided by a manufacturing method.

The above-mentioned problem is that the degree of acetalization when acetalized with monoaldehyde is 15 to 80 mol%, or the degree of acetalization when acetalized with dialdehyde is 0.1 to 15 mol%, and the polyvinyl alcohol contains a monomer unit containing a carboxylate, the content of the monomer unit is 1 to 7 mol%, the molded product (B) is a particle having an equivalent sphere diameter of 1 to 8 mm, and the molded product The problem can also be solved by providing a molding (B) in which (B) has continuous pores and has a water content of 0.2 to 70% by mass.

The shaped product (B) is obtained by removing moisture from the porous hydrogel shaped product (A) having a water content of 90 to 98% by mass by at least one method of pressurization, heating and air drying.

The molded product (B) can be packed in a container, and the packed product can be transported or stored.

A preferred embodiment of the present ^invention is a porous hydrogel shaped article (C ). A microbial carrier comprising this molding (C) is also a preferred embodiment of the present invention. A wastewater treatment method in which wastewater is treated with microorganisms supported on the carrier is also a preferred embodiment of the present invention.

According to the present invention, it is possible to provide a shaped article made of porous hydrogel that exhibits good volume restoration properties when it is immersed in water after being stored after being reduced in volume by compression, drying, or the like.

The porous hydrogel shaped article (A) of the present invention contains polyvinyl alcohol acetalized with monoaldehyde or dialdehyde.

Conventional hydrogel moldings have had the problem that when water is removed by compression or drying to reduce the volume, the hydrogel moldings do not swell even when immersed in water and are difficult to restore to the original hydrogel moldings. Therefore, the hydrous gel molded product must be transported in a state of being immersed in water, resulting in a large transportation cost. As a result of intensive studies by the present inventors, even if the volume is reduced by removing water by squeezing or drying, the porous hydrogel can be swelled by being immersed in water and restored to the original hydrogel molding. The molding (A) was invented. Moreover, it was also shown that the shaped porous hydrogel (A) and the restored shaped hydrogel (C) are useful as microorganism carriers.

The porous hydrogel molded article (A) of the present invention is a porous hydrogel molded article (A) containing polyvinyl alcohol acetalized with monoaldehyde or dialdehyde; The degree of acetalization is 15 to 80 mol%, or the degree of acetalization when acetalized with dialdehyde is 0.1 to 15 mol%, and the polyvinyl alcohol contains a monomer unit containing a carboxylate, The content of the monomer unit is 1 to 7 mol %, and the shaped porous hydrogel (A) has continuous pores and a specific surface area of 2 to 15 m ² /g. is.

The molded product (A) of the present invention can be obtained by acetalizing PVA as a raw material with monoaldehyde or dialdehyde. At this time, polyvinyl alcohol containing a monomer unit containing a carboxyl group or a derivative thereof (hereinafter sometimes referred to as raw material PVA) can be preferably used as the raw material PVA.

The production method of the raw material PVA is not particularly limited, but a preferred production method is to obtain a polyvinyl ester by polymerizing a vinyl ester in the presence of a monomer containing a carboxyl group or a derivative thereof, and then saponifying the polyvinyl ester. It is a way to By this method, raw material PVA can be suitably obtained.

Vinyl esters used in the production of raw material PVA include, for example, vinyl acetate, vinyl formate, vinyl propionate, vinyl caprylate, and vinyl versatate, among which vinyl acetate is preferred from an industrial point of view.

As the monomer containing a carboxyl group or a derivative thereof used in the production of raw material PVA, any monomer can be used as long as it can be copolymerized with a vinyl ester and forms a carboxylate by subsequent hydrolysis. Examples of monomers containing carboxyl groups include carboxyl group-containing monomers such as (meth)acrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid and itaconic acid. Examples of monomers containing derivatives of a carboxyl group include (meth)acrylic acids such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate. Ester; Salts of (meth)acrylic acid; Maleic acid esters such as monomethyl maleate, dimethyl maleate, monoethyl maleate, and diethyl maleate; Salts of maleic acid; Monomethyl fumarate, dimethyl fumarate, monoethyl fumarate, fumaric acid fumaric acid esters such as diethyl; fumaric acid salts; methyl crotonate, ethyl crotonate and other crotonic acid esters; crotonic acid salts; itaconic acid esters such as monomethyl itaconate, dimethyl itaconate, monoethyl itaconate and diethyl itaconate and salts of itaconic acid. Among them, acrylic acid esters are preferably used, and methyl acrylate is more preferably used, in consideration of reactivity during the modification reaction, availability, and the like. That is, the raw material PVA preferably contains a monomer unit derived from an acrylate ester, and more preferably contains a monomer unit derived from methyl acrylate.

As a method for incorporating a monomer unit containing a carboxyl group or a derivative thereof into the raw material PVA, as described above, a method of copolymerizing a monomer containing a carboxyl group or a derivative thereof with a vinyl ester and then saponifying the copolymer is used. Suitable methods include: Another method is to introduce a carboxyl group or a derivative thereof into vinyl alcohol units contained in unmodified PVA. At this time, a molded article may be produced after introducing a carboxyl group or a derivative thereof into unmodified PVA, or after producing a molded article using unmodified PVA, A carboxyl group or derivative thereof may be introduced.

In raw PVA, the content of monomer units containing a carboxyl group or a derivative thereof is preferably 1 to 7 mol %. The molded product (A) of the present invention can be obtained when the content is within the above range. Here, the derivatives of carboxyl group include salts and esters of carboxyl group. A carboxyl group may react with an adjacent hydroxyl group to form a lactone, and this lactone is also included in derivatives of the carboxyl group. The content of monomeric units containing a carboxyl group or a derivative thereof in raw material PVA can be measured using NMR.

The monoaldehyde used in the present invention includes formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and the like. Among them, formaldehyde is preferable from the viewpoint of cost and availability of the chemical solution.

The degree of acetalization of PVA contained in the molding (A) when acetalized with monoaldehyde is 15 to 80 mol %. If the degree of acetalization is less than 15 mol %, the required strength cannot be obtained in the molding (A). The degree of acetalization is preferably 25 mol % or more. On the other hand, when the degree of acetalization exceeds 80 mol %, the molded article (A) becomes more hydrophobized, resulting in significant volume shrinkage and reduced volume recovery after volume-reduced storage. The degree of acetalization is preferably 60 mol % or less.

On the other hand, the dialdehyde used in the present invention includes glyoxal, malonaldehyde, succinaldehyde, glutaraldehyde, adipaldehyde, malealdehyde, tartaraldehyde, citraldehyde, phthalaldehyde, isophthalaldehyde, terephthalaldehyde and the like. Among them, glutaraldehyde is preferable from the viewpoint of cost and availability of the chemical solution.

The degree of acetalization of PVA contained in the molding (A) when acetalized with dialdehyde is 0.1 to 15 mol %. If the degree of acetalization is less than 0.1 mol %, the required strength cannot be obtained in the molding (A). The degree of acetalization is preferably 0.2 mol % or more. On the other hand, if the degree of acetalization exceeds 15 mol %, the molded product (A) will be hydrophobized, causing significant volume shrinkage and impairing the swelling property. The degree of acetalization is preferably 10 mol % or less, more preferably 5 mol % or less.

If importance is placed on volume recovery after volume reduction, a porous hydrogel molding (A) containing polyvinyl alcohol acetalized with monoaldehyde is suitable. Moreover, when emphasizing the swelling property of the molded article, the porous hydrogel molded article (A) containing polyvinyl alcohol acetalized with dialdehyde is suitable.

It is important that the PVA contained in the molded product (A) contains a monomer unit containing a carboxylate, and the content of the monomer unit is 1 to 7 mol %. Since the PVA contained in the molded article (A) contains a monomer unit containing a carboxylate, the volume recovery property when immersed in water is improved. If the content is less than 1 mol%, good volume recovery cannot be obtained. The content is preferably 2 mol % or more. On the other hand, when the content exceeds 7 mol %, swelling of the molded article (A) becomes remarkable, shape retention of the molded article (A) is deteriorated, and strength is extremely lowered. The content is preferably 6 mol % or less.

Cationic species of carboxylates include alkali metal ions such as lithium, sodium, potassium, rubidium and cesium ions; alkaline earth metal ions such as magnesium, calcium, strontium and barium ions; aluminum ions and other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like.

The content of the carboxylate-containing monomeric unit in the moldings (A) to (C) can be determined based on the spectrum obtained by infrared spectroscopy (IR). In the measurement, an infrared spectrophotometer "Nicolet iS10" manufactured by Thermo SCIENCE can be used.

In the obtained IR spectrum, the area of the peaks (2990 to 2560 cm ^-1 ) derived from the vinyl alcohol unit and the methylene group and methine group of the monomer unit containing the carboxyl group or its derivative is determined. Also, the area of the peak (1625 to 1510 cm ⁻¹ ) derived from the carboxylate group of the monomer unit containing the carboxylate is determined. Then, the content (mol %) of monomeric units containing a carboxylate is calculated based on the following formula. 13.07 in the following formula is a coefficient for calculating the content of monomeric units including carboxylate. This coefficient is obtained from a calibration curve prepared in advance.
Content of monomer unit containing carboxylate (mol%) = 13.07 × (area of peak derived from carboxylate group)/(area of peak derived from methylene group and methine group)

It is important that the molding (A) has continuous pores. When the molded article (A) is used as a microorganism carrier, the molded article (A) having continuous pores can support many microorganisms. Here, the continuous holes do not mean that the holes exist independently, but that the holes communicate with each other. Continuous pores can be confirmed by observing the molding (A) using an electron microscope.

It is important that the molding (A) has a specific surface area of 2 to 15 m ² /g. The specific surface area includes the surface area of the molding (A) and the area of the PVA skeleton that forms the internal continuous pores. If the specific surface area is less than 2 m ² /g, when used as a microorganism carrier, the amount of microorganisms adhered is reduced, and the biological treatment capacity per apparent volume of the carrier is reduced. The specific surface area is preferably 5 m ² /g or more. On the other hand, when the specific surface area exceeds 15 m ² /g, the continuous pores of the molding (A) become dense, and the energy and cost for volume reduction by dehydration and drying become excessive. The specific surface area is preferably 12 m ² /g or less.

The specific surface areas of the moldings (A) to (C) were measured by freeze-drying each molding as a pretreatment and using the Kr (krypton) adsorption method in the BET method. In the measurement, a specific surface area/pore distribution measuring device "BELSORP-MAX" manufactured by Microtrack Bell Co., Ltd. can be used.

The molded article (A) of the present invention is preferably particles having an equivalent spherical diameter of 2 to 10 mm. Equivalent sphere diameter is the diameter of a sphere having a volume equal to that of the particle. When treating wastewater using a microbial carrier, a treatment tank is usually provided with a screen (filtration section). In this case, the opening of the screen must be smaller than the sphere equivalent diameter of the carrier in order to prevent the carrier from flowing out. Therefore, when the shaped article (A) is used as a microorganism carrier, if the equivalent sphere diameter of the shaped article (A) is small, the opening of the screen must also be small. Therefore, sludge and foreign matter may easily clog the screen. From this point of view, the molded product (A) is preferably particles having an equivalent sphere diameter of 2 mm or more. More preferably, the molded article (A) is particles having an equivalent sphere diameter of 3 mm or more. On the other hand, if the equivalent sphere diameter is too large, the specific surface area of the carrier may decrease, and the biological treatment capacity per apparent volume of the carrier may decrease. Further, when the equivalent sphere diameter is large, the fluidity of the carrier in the treatment tank is lowered, so there is a possibility that the amount of aeration and the stirring power must be increased. From this point of view, it is preferable that the molded article (A) is particles having an equivalent sphere diameter of 10 mm or less. More preferably, the molded article (A) is particles having an equivalent sphere diameter of 6 mm or less.

The shape of the molded article (A) is not particularly limited, and examples thereof include a spherical shape, a disk shape, a rod shape, an ellipsoidal shape, a contact lens shape having irregularities, and a dome shape. Among them, a spherical shape is preferable from the viewpoint of excellent fluidity in the treatment tank.

It is preferable that the molded product (A) has a water content of 90 to 98% by mass. When used as a microbial carrier, if the water content is less than 90% by mass, the molded article (A) shrinks and the volume becomes smaller, the pore diameter of the continuous pores becomes smaller, and the volume recovery after volume-reduced storage decreases. There is a risk. More preferably, the water content is 92% by mass or more. When used as a water-retaining material including water-retaining material for agriculture, it is preferably at least 95% by mass from the viewpoint of water absorption. On the other hand, if the water content exceeds 98% by mass, the molded product (A) may be deteriorated in shape retention and strength. More preferably, the water content is 97% by mass or less.

The water content can be measured by sampling the drained molding (A), measuring its mass, placing it in a dryer, and calculating from the mass after drying and the mass before drying.
Moisture content (mass%) = [(mass of molded article (A) before drying - mass of molded article (A) after drying) / mass of molded article (A) before drying] x 100

The method for producing the molded article (A) of the present invention is not particularly limited, but a preferred production method is to prepare an aqueous solution containing polyvinyl alcohol containing a monomer unit containing a carboxyl group or a derivative thereof and a water-soluble polysaccharide in a polyhydric Step 1: dropwise addition to an aqueous solution containing a metal salt to cause gelation to obtain particles; Step 2 of adding to an aqueous solution having a pH of 0.2 to 5 mol/L and reacting with monoaldehyde or dialdehyde to acetalize the polyvinyl alcohol in the particles; and a step 3 of contacting with 8 or more aqueous solutions.

In step 1, an aqueous solution containing polyvinyl alcohol containing a monomer unit containing a carboxyl group or a derivative thereof and a water-soluble polysaccharide is added dropwise to an aqueous solution containing a polyvalent metal salt for gelation to obtain particles. Hereinafter, polyvinyl alcohol containing a monomer unit containing a carboxyl group or a derivative thereof may be referred to as raw material PVA. Modified PVA produced by the method described above can be suitably used as the raw material PVA.

In step 1, a mixed aqueous solution containing raw material PVA and water-soluble polysaccharide is prepared. Examples of water-soluble polysaccharides include alkali metal salts of alginic acid, carrageenan, mannan, and chitosan. Sodium alginate is preferred from the viewpoint of availability. Sodium alginate is a type of polysaccharide mainly produced from brown algae (such as kelp), and is formed from sodium salts of monosaccharides having carboxyl groups, α-L-guluronic acid and β-D-mannuronic acid.

The starting PVA concentration of the mixed aqueous solution in step 1 is preferably 2 to 15% by mass. The higher the concentration of raw material PVA, the stronger the gel formed, but if the necessary gel strength is obtained, the lower the concentration of raw material PVA, the more advantageous from the raw material cost point of view. The concentration of the water-soluble polysaccharide in the aqueous solution in step 1 is preferably 0.2 to 4% by mass, more preferably 0.5 to 2% by mass, from the viewpoint of gel moldability.

By bringing the mixed aqueous solution prepared as described above into contact with an aqueous solution containing a polyvalent metal salt, it is possible to obtain particles of various shapes. In this specification, the aqueous solution when the mixed aqueous solution is brought into contact with the aqueous solution containing the polyvalent metal salt to be coagulated is referred to as the coagulating liquid.

Cationic species of polyvalent metal salts include alkaline earth metals such as calcium, magnesium, strontium, and barium; aluminum, nickel ions, cerium, and the like. Among them, alkaline earth metals are suitable as the cationic species of the polyvalent metal salt. The concentration of the polyvalent metal salt in the coagulation liquid is preferably 0.03-0.5 mol/L.

The method of contacting is not particularly limited, but a method of dropping the mixed aqueous solution into the coagulation liquid from the air or a method of contacting in the liquid may be used, and a commonly used contact method can be appropriately selected and used. By dropping the mixed aqueous solution into the coagulation liquid, an ionic bond is formed between the water-soluble polysaccharide and the cation of the polyvalent metal salt, and the particles become spherical. At this time, most of the raw material PVA and water-soluble polysaccharide in the mixed aqueous solution are taken into the gelled particles, and the amount of them eluted into the coagulation liquid is small.

Next, in step 2, the particles obtained in step 1 have a pH of 3 or less, contain a metal salt, and have a cation concentration of the metal salt multiplied by a valence of 0.2 to 5 mol/L. and reacted with monoaldehyde or dialdehyde to acetalize the polyvinyl alcohol in the particles. In this specification, an aqueous solution having a pH of 3 or less and containing a metal salt is referred to as an acetalization reaction solution.

In step 2, an acetalization reaction solution having a pH of 3 or less and containing a metal salt is prepared. Examples of the acid contained in the acetalization reaction solution include acids such as sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, acetic acid and oxalic acid, and acid salts such as sodium hydrogensulfate and ammonium hydrogensulfate. Among them, sulfuric acid is preferable in terms of versatility and cost. If the acid concentration is low, the reaction takes a long time and the amount of PVA eluted from the particles increases.

Examples of metal salts include sulfates, hydrochlorides, phosphates, nitrates, acetates, oxalates, and tartrates, among which sulfates and hydrochlorides are preferred. Examples of cationic species include alkali metals and alkaline earth metals. In the acetalization reaction solution, the value obtained by multiplying the concentration of the metal cation by the valence is preferably 0.2 to 5 mol/L. If the value obtained by multiplying the concentration of the metal cation by the valence is less than 0.2 mol/L, there is a risk that a porous structure will not be formed in the molded article, or that the amount of PVA eluted into the reaction solution will increase. It is more preferably 4 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, when the metal salt contained in the acetalization reaction solution is sodium sulfate (Na ₂ SO ₄ ), the value obtained by multiplying the concentration of sodium ion by 1. It's about. 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 sodium ion concentration by 1. Therefore, when the sodium chloride concentration is 1 mol/L, the value is 1 mol/L. When the metal salt is magnesium sulfate (MgSO 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 liquid when the particles are brought into contact with the acetalization reaction liquid is preferably 20 to 80°C. If the temperature is less than 20° C., the reaction time becomes long, and there is a risk that the raw material PVA may be eluted into the acetalization reaction solution. On the other hand, if the temperature exceeds 80° C., corrosion of the plant by acid is severe, which is not preferable.

By bringing the particles obtained in step 1 into contact with the acetalization reaction solution, the PVA in the particles is acetalized. As the acetalization reaction progresses, phase separation is induced between the polyvinyl alcohol-rich region and the water-rich region. A porous structure is formed in the

In the above production method, when producing a molded product having continuous pores with a large pore size, cornstarch, tapioca starch, potato starch, various modified starches, etc. are added to the mixed aqueous solution as necessary, and in step 2, It is also possible to increase the temperature at which the particles are brought into contact with the acetalization reaction solution to the gelatinization temperature or higher to promote phase separation by gelatinization, thereby producing a molding having continuous pores with a large pore size.

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 simultaneously. After gelling to obtain particles, they may be acetalized. Alternatively, gelation may be performed after acetalization. Above all, it is preferable to perform Step 1 and Step 2 in this order.

When acetalization is performed using monoaldehyde, the concentration of monoaldehyde in the acetalization reaction solution is preferably 0.01 to 1.5 mol/L. When the monoaldehyde concentration is less than 0.01 mol/L, the acetalization reaction does not proceed efficiently, and there is a risk that a large amount of raw material PVA will be eluted from the molded product (A) obtained. More preferably, the monoaldehyde concentration is 0.3 mol/L or more. On the other hand, if the concentration of monoaldehyde exceeds 1.5 mol/L, the molded product (A) obtained becomes brittle, and there is a possibility that the shrinkage during the production process will increase and the moisture content will decrease. Moreover, when the molding (A) is used as a microorganism carrier, the shrinkage of the molding (A) may reduce the habitability of microorganisms. Therefore, when the waste water is decomposed, there is a possibility that the decomposition efficiency is lowered. More preferably, the monoaldehyde concentration is 1.0 mol/L or less. By setting the concentration of monoaldehyde in such a range, it is possible to obtain a molding (A) having excellent microbial habitability.

In the case of acetalization using dialdehyde, the dialdehyde concentration in the acetalization reaction solution is preferably 0.001 to 0.02 mol/L. When the dialdehyde concentration is less than 0.001 mol/L, the acetalization reaction does not proceed efficiently, resulting in insufficient cross-linking, which may increase the elution of raw material PVA from the obtained molding (A). More preferably, the dialdehyde concentration is 0.003 mol/L or more. On the other hand, if the dialdehyde concentration exceeds 0.02 mol/L, the molded article (A) to be obtained becomes brittle, and there is a possibility that the shrinkage during the manufacturing process will increase and the moisture content will decrease. Moreover, when the molding (A) is used as a microorganism carrier, the shrinkage of the molding (A) may reduce the habitability of microorganisms. Therefore, when the waste water is decomposed, there is a possibility that the decomposition efficiency is lowered. More preferably, the dialdehyde concentration is 0.015 mol/L or less. By setting the dialdehyde concentration in such a range, it is possible to obtain a molding (A) having excellent microbial habitability.

Next, in step 3, the particles obtained in step 2 are brought into contact with an aqueous solution having a pH of 8 or higher. By bringing the particles into contact with the aqueous solution, the carboxyl group or derivative thereof contained in PVA becomes a carboxylate. That is, free carboxyl groups form salts, and esters are hydrolyzed to carboxyl groups to form salts. As the aqueous solution used at this time, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferably used.

The shaped product (A) thus obtained has high biocompatibility, has continuous pores, and can carry a large amount of microorganisms, and is suitably used as a microorganism carrier. In addition, when the volume is reduced by removing moisture by pressing or drying, the volume can be sufficiently increased by immersing it in water, so that the volume recovery property is good.

Further, the molding (B) of the present invention is a porous gel molding (B) containing polyvinyl alcohol acetalized with monoaldehyde or dialdehyde; the degree of acetalization when acetalized with monoaldehyde is 15 to 80 mol%, or the degree of acetalization when acetalized with a dialdehyde is 0.1 to 15 mol%, the polyvinyl alcohol contains a monomer unit containing a carboxylate, and the monomer The body unit content is 1 to 7 mol%, the molded article (B) is a particle having an equivalent sphere diameter of 1 to 8 mm, the molded article (B) has continuous pores, and the molded article (B) has a water content of 0.2 to 70% by mass.

The molded article (B) is different from the molded article (A) in that the molded article (B) is a particle having an equivalent sphere diameter of 1 to 8 mm and a water content of 0.2 to 70% by mass. The rest of the structure is the same as that described above for the molded article (A). The molded article (B) has a smaller equivalent sphere diameter and a smaller water content than the molded article (A), and has a reduced volume, so that the storage space can be reduced and the handling property is also excellent. From this point of view, the molded article (B) is preferably particles having an equivalent sphere diameter of 5 mm or less, more preferably particles having an equivalent sphere diameter of 3 mm or less. The moisture content of the molding (B) is preferably 50% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. On the other hand, when water is removed from the molded product (A) to produce the molded product (B), energy is required to remove the water. From the viewpoint of energy saving, the molded article (B) is preferably particles having an equivalent spherical diameter of 1.5 mm or more, and more preferably has a moisture content of 0.5% by mass or more. .

The method for producing the molding (B) is not particularly limited, but a preferred production method is a method of removing water from the porous hydrogel molding (A) having a water content of 90 to 98% by mass. Although the method for removing moisture from the molded product (A) is not particularly limited, it is preferable to remove moisture from the molded product (A) by at least one method of pressurization, heating, and air drying. Examples of pressurization methods include a method of physically applying pressure using a compressor and a method of using a centrifugal separator. Examples of the heating method include a method using a fluidized bed dryer and a hot air blower dryer. A blow dryer can be used for blow drying. These methods can be used in combination so as to obtain the desired equivalent sphere diameter and water content, and they are appropriately selected in consideration of costs and the like.

A preferred embodiment of the present invention is a packed product in which the molding (B) is placed in a container. As a container for packing a relatively large amount of molding (B), an IBC container, a flexible container bag, and the like can be mentioned. Examples of a container for packing a relatively small amount of molded product (B) include polyethylene bags and corrugated cardboard. Further, in the transportation method described later, for example, when using a tank truck (vehicle) or a tank car (railway), the tank itself may serve as a container.

Also, a preferred embodiment of the present invention is a transportation method for transporting the above packed goods. Examples of the transportation method include a method of manually transporting by a worker, and a method of transporting by truck, railroad, ship, or aircraft. A storage method for storing the above packed goods is also a preferred embodiment of the present invention. The storage method is not particularly limited, and a plurality of containers can be stacked and stored. The temperature during transportation and storage is preferably 10 to 40°C.

The molded article (B) of the present invention has good volume recovery when swollen with water. Therefore, a porous hydrogel molding (C) having a specific surface area of 2 to 15 m ² /g and a water content of 90 to 98% by mass, which is obtained by swelling the molding (B) with water, is a preferred embodiment. . The method for producing the molding (C) is not particularly limited, but a preferred production method is to immerse the molding (B) in water to swell it. At this time, the molded article (B) may be immersed in water and left to stand, or the molded article (B) may be immersed in water and then allowed to flow. From the viewpoint of sufficiently swelling the molded article (B), it is preferable to immerse the molded article (B) in water and then allow it to stand and flow for at least one day.

The molded product (C) thus obtained can be suitably used as a microbial carrier for wastewater treatment or a carrier for a biocatalyst. Furthermore, it can be used as a water-retaining material including agricultural water-retaining material, an artificial culture medium, a cooling agent, an alternative to biogels for eyes, skin, joints, etc., a sustained-release material for drugs, and a base material for actuators.

A preferred embodiment of the present invention is a microbial carrier consisting of a molding (C). A wastewater treatment method in which wastewater is treated with microorganisms supported on the carrier is also a preferred embodiment. As a treatment method at this time, the molded product (B) is put into a tank or tank containing water, the molded product (B) is swollen with water to obtain a molded product (C), and then the molded product (C ) is transported to a wastewater treatment tank by a pump. Alternatively, the molded article (B) may be directly put into a wastewater treatment tank, and the molded article (B) may be swollen with water in the treatment tank to obtain the molded article (C).

The molding (C) obtained by swelling with water and the sludge as the inoculum are mixed in a wastewater treatment tank, and the water to be treated is continuously introduced into the molding (C) to support the microorganisms. be able to. By doing so, the molding (C) can function as a microorganism carrier.

Microorganisms carried on the carrier may be anaerobic microorganisms or aerobic microorganisms. The type of microorganisms may be appropriately selected according to the dirt and type of wastewater to be treated.

As described above, the molded article (A) of the present invention is useful as a microbial carrier, a water-retaining material such as an agricultural water-retaining material, or an artificial culture medium, and can be reduced in volume by removing water by pressing, drying, or the like. It is excellent in transportability and storage because it can be done. Then, the molded article (B) from which moisture has been removed can be restored to the hydrous gel molded article (C) by swelling with water. The molded article (C) thus obtained is useful as a microorganism carrier, a water-retaining material including agricultural water-retaining material, and an artificial culture medium.

Example 1
602 g of vinyl acetate, 1.21 g of methyl acrylate, and 254 g of methanol were charged into a reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, and an initiator addition port, and the reactor was stirred for 30 minutes with nitrogen bubbling. It was replaced with active gas. A water bath was heated to start raising the temperature of the reactor, and when the internal temperature reached 60° C., 0.16 g of azobisisobutyronitrile (AIBN) was added as an initiator to initiate polymerization. Appropriate sampling was performed to confirm the progress of polymerization from the solid content concentration. asked for a rate. When the consumption rate reached 4%, the polymerization was terminated by cooling to 30°C. A vacuum line was connected and residual vinyl acetate was distilled off under reduced pressure together with methanol at 30°C. While visually confirming the inside of the reactor, when the viscosity increased, methanol was added as appropriate while distillation was continued to obtain polyvinyl acetate having a methyl acrylate unit content of 5.2 mol %. The content was measured using NMR. Next, 1 g of the obtained methyl acrylate unit-containing polyvinyl acetate and 18.2 g of methanol were added and dissolved in the same reactor as above. The water bath was heated and the mixture was heated and stirred until the internal temperature of the reactor reached 70°C. 0.78 g of a methanol solution of sodium hydroxide (concentration: 15% by mass) was added thereto, and saponification was performed at 70° C. for 2 hours. The resulting solution was filtered to obtain polyvinyl alcohol 1 (PVA1) having a methyl acrylate unit content of 5.2 mol %.

Water was added so that the PVA1 content was 7% by mass, and the mixture was treated in hot water for 50 minutes to dissolve the PVA1. To this PVA1 aqueous solution, sodium alginate was added so as to make it 0.9% by mass, and the mixture was stirred and dissolved for 30 minutes to prepare a mixed aqueous solution. 300 g of this mixed aqueous solution was fed by a roller pump equipped with a silicon tube hose with an inner diameter of 3.2 mm and a nozzle with an inner diameter of 3 mm attached to the tip, and stirred with a stirrer to form a solidified calcium chloride aqueous solution with a concentration of 0.3 mol / L. Dropped into 1 L bath. The dropped droplets were spherically gelled and precipitated in the aqueous calcium chloride solution.

This spherical molded product was separated from the calcium chloride aqueous solution and immersed in 1 L of the acetalization reaction solution at 40° C. for 45 minutes. Here, the acetalization reaction solution is an aqueous solution containing 250 g/L of sulfuric acid, 100 g/L of sodium sulfate, and 50 g/L of formaldehyde. After that, the molded article was separated from the acetalization reaction solution, put into an aqueous sodium hydroxide solution (concentration: 24% by mass), washed while controlling the pH of the liquid at 12, and then washed with water. When the surface and cross section of the obtained hydrous gel molding were observed with an SEM, it was confirmed that continuous pores were present from the outer surface toward the center. This hydrous gel molding was spherical particles with a specific surface area of 6.9 m ² /g and an equivalent spherical diameter of 5.2 mm, and the water content was 95% by mass. The degree of acetalization of PVA in the hydrous gel molding was 56 mol %, and the content of sodium acrylate units was 4.8 mol %. The obtained sample was placed in a 1 L rectangular tank, and after aeration and fluidization for 1 hour at an air flow rate of 6 L/min, it was checked for damage, but no damage was observed and the shape retention of the molded product was good. (Evaluation A in Table 1). The results are summarized in Table 1.

Example 2
Water was added so that the PVA1 content was 7% by mass, and the mixture was treated in hot water for 50 minutes to dissolve the PVA1. To this PVA1 aqueous solution, sodium alginate was added so as to make it 0.9% by mass, and the mixture was stirred and dissolved for 30 minutes to prepare a mixed aqueous solution. 300 g of this mixed aqueous solution was fed by a roller pump equipped with a silicon tube hose with an inner diameter of 3.2 mm and a nozzle with an inner diameter of 2 mm attached to the tip, and stirred with a stirrer to form a solidified aqueous solution of calcium chloride with a concentration of 0.3 mol / L. Dropped into 1 L bath. The dropped droplets were spherically gelled and precipitated in the aqueous calcium chloride solution.

This spherical molded product was separated from the calcium chloride aqueous solution and immersed in 1 L of the acetalization reaction solution at 40° C. for 45 minutes. Here, the acetalization reaction solution is an aqueous solution containing 10 g/L of sulfuric acid, 100 g/L of sodium sulfate, and 0.8 g/L of glutaraldehyde. After that, the molded article was separated from the acetalization reaction solution, put into an aqueous sodium hydroxide solution (concentration: 24% by mass), washed while controlling the pH of the liquid at 12, and then washed with water. When the surface and cross section of the obtained hydrous gel molding were observed with an SEM, it was confirmed that continuous pores were present from the outer surface toward the center. This hydrous gel molding was spherical particles with a specific surface area of 9.3 m ² /g and an equivalent spherical diameter of 4.8 mm, and the water content was 97% by mass. The degree of acetalization of PVA in the hydrous gel molding was 0.9 mol %, and the content of sodium acrylate units was 4.9 mol %. The obtained sample was placed in a 1 L rectangular tank, and after aeration and fluidization for 1 hour at an air flow rate of 6 L/min, the presence or absence of damage was checked, but no damage was observed and the shape retention was good. (Evaluation A in Table 1). The results are summarized in Table 1.

Comparative example 1
Water was added to unmodified PVA2 (average degree of polymerization: 1700, degree of saponification: 99.8 mol%), and the mixture was treated in hot water for 50 minutes to dissolve PVA2 (concentration: 7 mass%). Sodium alginate was added to this PVA2 aqueous solution so as to be 0.9% by mass, and the mixture was stirred for 30 minutes to dissolve. Furthermore, 100 g of this mixed aqueous solution was fed by a roller pump equipped with a silicon tube hose with an inner diameter of 3.2 mm and a nozzle with an inner diameter of 4 mm at the tip, and stirred with a stirrer to form an aqueous solution of calcium chloride with a concentration of 0.3 mol / L. Dropped into 1 L of coagulation bath. The dropped droplets were spherically gelled and precipitated in the aqueous calcium chloride solution.

This spherical molded product was separated from the calcium chloride aqueous solution and immersed in 1 L of the acetalization reaction solution at 40° C. for 90 minutes. Here, the acetalization reaction solution is an aqueous solution containing 200 g/L of sulfuric acid, 100 g/L of sodium sulfate, and 50 g/L of formaldehyde. After that, the molded article was separated from the acetalization reaction liquid, put into an aqueous sodium hydroxide solution (concentration: 24% by mass), washed while controlling the pH of the liquid at 12, and then washed with water. When the surface and cross section of the obtained hydrous gel molding were observed with an SEM, it was confirmed that continuous pores were present from the outer surface toward the center. The hydrous gel molding was spherical particles with a specific surface area of 16 m ² /g and an equivalent spherical diameter of 4.0 mm, and the water content was 88% by mass. The degree of acetalization of PVA in the hydrous gel molding was 54 mol %, and the content of sodium acrylate units was 0 mol %. The obtained sample was placed in a 1 L rectangular tank, and after aeration and fluidization for 1 hour at an air flow rate of 6 L/min, the presence or absence of damage was checked, but no damage was observed and the shape retention was good. (Evaluation A in Table 1). The results are summarized in Table 1.

Comparative example 2
Water was added so that the PVA2 content was 7% by mass, and the mixture was treated in hot water for 50 minutes to dissolve the PVA2. Sodium alginate was added to this PVA2 aqueous solution so as to be 0.9% by mass, and the mixture was stirred for 30 minutes to dissolve. Furthermore, 100 g of this mixed aqueous solution was fed by a roller pump equipped with a silicon tube hose with an inner diameter of 3.2 mm and a nozzle with an inner diameter of 2 mm at the tip, and stirred with a stirrer to form an aqueous solution of calcium chloride with a concentration of 0.3 mol / L. It was added dropwise to 1 L of coagulation bath. The dropped droplets were spherically gelled and precipitated in the aqueous calcium chloride solution.

This spherical molded product was separated from the calcium chloride aqueous solution and immersed in 1 L of the acetalization reaction solution at 40° C. for 90 minutes. Here, the acetalization reaction solution is an aqueous solution containing 10 g/L of sulfuric acid, 100 g/L of sodium sulfate, and 0.8 g/L of glutaraldehyde. After that, the molded article was separated from the acetalization reaction liquid, put into an aqueous sodium hydroxide solution (concentration: 24% by mass), washed while controlling the pH of the liquid at 12, and then washed with water. When the surface and cross section of the obtained hydrous gel molding were observed with an SEM, it was confirmed that continuous pores were present from the outer surface toward the center. The hydrous gel molding was spherical particles with a specific surface area of 17 m ² /g and an equivalent spherical diameter of 3.9 mm, and the water content was 91% by mass. The degree of acetalization of PVA in the hydrous gel molding was 1.5 mol %, and the content of sodium acrylate units was 0 mol %. The obtained sample was placed in a 1 L rectangular tank, and after aeration and fluidization for 1 hour at an air flow rate of 6 L/min, the presence or absence of damage was checked, but no damage was observed and the shape retention was good. (Evaluation A in Table 1). Table 1 summarizes the results.

Comparative example 3
602 g of vinyl acetate, 1.21 g of methyl acrylate, and 254 g of methanol were charged into a reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, and an initiator addition port, and the reactor was stirred for 30 minutes with nitrogen bubbling. It was replaced with active gas. A water bath was heated to start raising the temperature of the reactor, and when the internal temperature reached 60° C., 0.16 g of azobisisobutyronitrile (AIBN) was added as an initiator to initiate polymerization. Appropriate sampling was performed to confirm the progress of polymerization from the solid content concentration. asked for a rate. When the consumption rate reached 7%, the polymerization was stopped by cooling to 30°C. A vacuum line was connected and residual vinyl acetate was distilled off under reduced pressure together with methanol at 30°C. While visually confirming the inside of the reactor, when the viscosity increased, methanol was added as appropriate while distillation was continued to obtain polyvinyl acetate having a methyl acrylate unit content of 8.4 mol %. The content was measured using NMR. Next, 1 g of the obtained methyl acrylate unit-containing polyvinyl acetate and 18.2 g of methanol were added and dissolved in the same reactor as above. A water bath was heated to heat and stir until the internal temperature reached 70°C. 0.78 g of a methanol solution of sodium hydroxide (concentration: 15% by mass) was added thereto, and saponification was performed at 70° C. for 2 hours. The resulting solution was filtered to obtain polyvinyl alcohol 3 (PVA3) having a methyl acrylate unit content of 8.4 mol %.

Water was added so that the PVA3 content was 7% by mass, and the mixture was treated in hot water for 50 minutes to dissolve the PVA3. Sodium alginate was added to this PVA3 aqueous solution so as to make it 0.9% by mass, and the mixture was stirred and dissolved for 30 minutes to prepare a mixed aqueous solution. 300 g of this mixed aqueous solution was fed by a roller pump equipped with a silicon tube hose with an inner diameter of 3.2 mm and a nozzle with an inner diameter of 4 mm attached to the tip, and stirred with a stirrer to form an aqueous solution of calcium chloride with a concentration of 0.3 mol / L. Dropped into 1 L bath. The dropped droplets were spherically gelled and precipitated in the aqueous calcium chloride solution.

This spherical molded product was separated from the calcium chloride aqueous solution and immersed in 1 L of the acetalization reaction solution at 40° C. for 45 minutes. Here, the acetalization reaction solution is an aqueous solution containing 250 g/L of sulfuric acid, 100 g/L of sodium sulfate, and 50 g/L of formaldehyde. After that, the molded product was separated from the acetalization reaction solution, put into an aqueous sodium hydroxide solution (concentration: 24% by mass), washed while controlling the pH of the solution at 12, and then washed with water. However, the volume expansion of the water-containing gel molding became extremely remarkable, the shape retention property deteriorated, the strength decreased, and the water-containing gel molding broke due to stirring (Evaluation B in Table 1). The content of sodium acrylate units was 7.5 mol %. The results are summarized in Table 1.

Comparative example 4
Water was added so that the PVA3 content was 7% by mass, and the mixture was treated in hot water for 50 minutes to dissolve the PVA3. Sodium alginate was added to this PVA3 aqueous solution so as to make it 0.9% by mass, and the mixture was stirred and dissolved for 30 minutes to prepare a mixed aqueous solution. 300 g of this mixed aqueous solution was fed by a roller pump equipped with a silicon tube hose with an inner diameter of 3.2 mm and a nozzle with an inner diameter of 2 mm attached to the tip, and stirred with a stirrer to form a solidified aqueous solution of calcium chloride with a concentration of 0.3 mol / L. Dropped into 1 L bath. The dropped droplets were spherically gelled and precipitated in the aqueous calcium chloride solution.

This spherical molded product was separated from the calcium chloride aqueous solution and immersed in 1 L of the acetalization reaction solution at 40° C. for 45 minutes. Here, the acetalization reaction solution is an aqueous solution containing 10 g/L of sulfuric acid, 100 g/L of sodium sulfate, and 0.8 g/L of glutaraldehyde. After that, the molded product was separated from the acetalization reaction solution, put into an aqueous sodium hydroxide solution (concentration: 24% by mass), washed while controlling the pH of the solution at 12, and then washed with water. Similarly, in Comparative Example 4, the volume expansion of the water-containing gel molded product during washing with water was extremely remarkable, the shape retention property deteriorated, the strength decreased, and the water-containing gel molded product broke due to stirring (Table 1). Evaluation B). The content of sodium acrylate units was 7.6 mol %. The results are summarized in Table 1.

Comparative example 5
Water was added so that the PVA1 content was 7% by mass, and the mixture was treated in hot water for 50 minutes to dissolve the PVA1. To this PVA1 aqueous solution, sodium alginate was added so as to make it 0.9% by mass, and the mixture was stirred and dissolved for 30 minutes to prepare a mixed aqueous solution. 300 g of this mixed aqueous solution was fed by a roller pump equipped with a silicon tube hose with an inner diameter of 3.2 mm and a nozzle with an inner diameter of 2 mm attached to the tip, and stirred with a stirrer to form a solidified aqueous solution of calcium chloride with a concentration of 0.3 mol / L. Dropped into 1 L bath. The dropped droplets were spherically gelled and precipitated in the aqueous calcium chloride solution.

This spherical molded product was separated from the calcium chloride aqueous solution and immersed in 1 L of the acetalization reaction solution at 40° C. for 45 minutes. Here, the acetalization reaction solution is an aqueous solution containing 200 g/L of sulfuric acid, 10 g/L of sodium sulfate, and 0.8 g/L of glutaraldehyde. After that, the molded product was separated from the acetalization reaction solution, put into an aqueous sodium hydroxide solution (concentration: 24% by mass), washed while controlling the pH of the solution at 12, and then washed with water. When the surface and cross section of the obtained hydrous gel molding were observed by SEM, no holes were confirmed on the outer surface or inside. The hydrous gel molding was spherical particles having a specific surface area of 0.4 m ² /g and an equivalent spherical diameter of 3.3 mm, and the water content was 88% by mass. The degree of acetalization of PVA in the hydrous gel molding was 15 mol %, and the content of sodium acrylate units was 4.7 mol %. The obtained sample was placed in a 1 L rectangular tank, and after aeration and fluidization for 1 hour at an air flow rate of 6 L/min, the presence or absence of damage was checked, but no damage was observed and the shape retention was good. (Evaluation A in Table 1). The results are summarized in Table 1.

[Volume reduction test]
The water-containing gel moldings obtained in Examples 1 and 2 and Comparative Examples 1, 2 and 5 were each reduced in volume by the following method.

method (a)
A pressure of 10 kPa was applied to the water-containing gel molding for 30 seconds to dehydrate it and reduce its volume.
method (b)
The water-containing gel molding was placed in a dryer and dried at 60°C for 4 hours to reduce the volume.
method (c)
After dehydrating the water-containing gel molding for 30 seconds by applying a pressure of 10 kPa for 30 seconds to reduce the volume, the obtained molding was placed in a dryer and dried at 90° C. for 30 minutes to further reduce the volume.

Then, the volume ratio (% by volume) after volume reduction was measured according to the following formula. In addition, according to the above formula, the moisture content of the compact after volume reduction was also measured. Table 2 shows the results.
Volume ratio after volume reduction (% by volume) = [(true volume of molded product after volume reduction) / (true volume of hydrous gel molded product before volume reduction)] × 100

After the molded product before volume reduction and the molded product obtained by methods (a) to (c) were placed in an aluminum inner bag and sealed, the aluminum inner bag was subjected to a pressure of 10 kPa and heated to 60 ° C. Stored in the dryer for 3 weeks. These storage conditions are conditions assuming storage of a 1-ton molded product in a flexible container bag. After 3 weeks had passed, the molded article was taken out from the flexible container bag, immersed in a sufficient amount of water, and allowed to stand at room temperature. After 24 hours, the molding was taken out from the water, the volume and particle size were measured, and the volume recovery rate was calculated. Here, the volume recovery rate (% by volume) is a value determined by the following formula. Table 2 shows the results.
Volume recovery rate (% by volume) = [(true volume of molded product after immersion in water) / (true volume of hydrous gel molded product before volume reduction)] × 100

As shown in Table 2, the hydrogel moldings of Examples 1 and 2 were immersed in water and restored to approximately the same volume as before volume reduction even after volume reduction and storage. On the other hand, the water-containing gel shaped articles of Comparative Examples 1 and 2 did not restore to the same volume as before volume reduction, and had poor volume restoring properties. At this time, the result was that the smaller the volume of the molded product after volume reduction, the lower the volume recovery property. In addition, although the hydrous gel molding of Comparative Example 5 did not have continuous pores, the volume restoring property was not bad.

[Wastewater treatment test]
The water-containing gel moldings of Examples 1 and 2 and Comparative Examples 1, 2 and 5 were used as carriers for microorganisms to treat waste water. In addition, as Example 3, the water-containing gel molded product of Example 1 was reduced in volume by the method (c), and then stored and restored in the same manner as in Example 1. processed. Conditions for wastewater treatment are as follows.

An ammonia nitrification test was conducted using a nitrification-based ammonia removal wastewater treatment system. As the aeration tank, an aeration tank having a tank volume of 1 liter was used, and the carrier was filled with a bulk volume of 100 ml corresponding to 10% of the capacity. Further, sewage sludge was put into the same tank so that MLSS (Mixed Liquor Suspended Solid) was 4000 mg/L. Aeration was carried out continuously with a water bath temperature in the range of 25-30° C., supplying 3.5 L/min of air from a porous air diffuser. Simulated wastewater containing 270 mg/L of ammonium chloride and 2800 mg/L of sodium bicarbonate was continuously supplied starting from 400 ml/day, and the ammonia volume load was started from 0.03 kg/(m ³ d). It was given to the same tank, and while the sludge was discharged out of the tank, the volumetric load was gradually increased, and the treatment was carried out for 60 days, and the removal amount of ammonia was observed.

The removal amount of ammonia is calculated by the following formula using the raw water ammonia concentration (mg/L), treated water ammonia concentration (mg/L), wastewater flow rate (L/d), and tank volume (L).
Ammonia removal amount = (Ammonia concentration in raw water - Ammonia concentration in treated water) x Wastewater flow rate x 10 ^-9 / (Tank volume x 10 ^-3 )

The number of bacteria in the carrier was measured by the following method. After 60 days from the start of the test, several carriers were sampled from the aeration tank, purified water was added, and the carrier was washed several times until no floating matter was left. Sterilized water was added to the carrier, the carrier was pulverized with a homogenizer, and the supernatant was collected. Lumitester K-200 manufactured by Kikkoman Biochemifa was used to perform emission spectrometry on the supernatant, and ATP (adenosine triphosphate) extracted in 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 the carrier and sterilized water) and the bulk specific gravity data of the carrier.

Table 3 shows the results of the amount of ammonia removed. For Examples 1 and 2 and Comparative Examples 1 and 2, after about 40 days, the amount of ammonia removed reached 0.6 kg/(m ³ ·d), and a sufficient amount of bacteria in the carrier adhered. rice field. Example 3 also had the same processability and the same amount of bacteria as Examples 1 and 2 and Comparative Examples 1 and 2, and it was also shown that the restored hydrous gel molding is also useful as a microorganism carrier. .

In Comparative Example 5, the amount of ammonia removed after 60 days was 0.3 kg/(m ³ ·d), which was about half that of other Examples and Comparative Examples. The number of microbes supported on the carrier after 60 days was clearly lower than that of other carriers. It is considered that this is because continuous pores are not formed from the surface to the inside, thereby reducing the adhesion area of microorganisms.

Claims (14)

A porous hydrogel molding (A) containing polyvinyl alcohol acetalized with monoaldehyde or dialdehyde;
The degree of acetalization when acetalized with monoaldehyde is 15 to 80 mol%, or the degree of acetalization when acetalized with dialdehyde is 0.1 to 15 mol%,
The polyvinyl alcohol contains a monomer unit containing a carboxylate, and the content of the monomer unit is 1 to 7 mol%,
A shaped article (A) of porous hydrogel, characterized in that the shaped article (A) has continuous pores and a specific surface area of 2 to 15 m ² /g. The shaped article (A) of porous hydrogel according to claim 1, which is a particle having an equivalent spherical diameter of 2 to 10 mm. 3. The porous hydrogel molding (A) according to claim 1 or 2, which has a water content of 90 to 98% by mass. A microorganism carrier comprising the shaped article (A) according to claim 3. A method for producing a molded article (A) according to any one of claims 1 to 3;
Step 1 of obtaining particles by dropping an aqueous solution containing polyvinyl alcohol containing a monomer unit containing a carboxyl group or a derivative thereof and a water-soluble polysaccharide into an aqueous solution containing a polyvalent metal salt to gel the solution;
The obtained particles are added to an aqueous solution having a pH of 3 or less, containing a metal salt, and having a value obtained by multiplying the cation concentration of the metal salt by the valence of 0.2 to 5 mol/L. step 2 of reacting with an aldehyde to acetalize the polyvinyl alcohol in the particles;
A method for producing a molding (A), comprising a step 3 of bringing the particles obtained in step 2 into contact with an aqueous solution having a pH of 8 or higher. A porous gel molding (B) comprising polyvinyl alcohol acetalized with monoaldehyde or dialdehyde;
The degree of acetalization when acetalized with monoaldehyde is 15 to 80 mol%, or the degree of acetalization when acetalized with dialdehyde is 0.1 to 15 mol%,
The polyvinyl alcohol contains a monomer unit containing a carboxylate, and the content of the monomer unit is 1 to 7 mol%,
The molding (B) is particles having an equivalent sphere diameter of 1 to 8 mm,
A molded article (B) having continuous pores and having a water content of 0.2 to 70% by mass. 7. The method for producing a molding (B) according to claim 6, wherein water is removed from the porous hydrogel molding (A) having a water content of 90 to 98% by mass. 8. The method for producing a molded article (B) according to claim 7, wherein moisture is removed from the molded article (A) by at least one method of pressurization, heating and air drying. A packaged product in which the molded article (B) according to claim 6 is placed in a container. A transport method for transporting the packaged goods according to claim 9 . A storage method for storing the packaged goods according to claim 9 . A porous hydrogel molding (C) having a specific surface area of 2 to 15 m ² /g and a water content of 90 to 98% by mass, which is obtained by swelling the molding (B) according to claim 6 with water. A microorganism carrier comprising the shaped article (C) according to claim 12. A wastewater treatment method for treating wastewater with the microorganism supported on the carrier according to claim 13.