WO1999036464A1 - Spongy porous spherical particles and process for producing the same - Google Patents

Abstract

Spongy porous spherical particles which are excellent in strength and handleability and have a polyvinyl acetal skeleton. The particles are characterized by (1) having spaces through which a microorganism, etc., is freely movable, (2) having inner walls to which a microorganism can adhere, (3) having flowability, (4) having excellent mechanical strength (wearing resistance), (5) having elasticity, and hence having a prolonged life when used as a carrier. The particles are further characterized in that (6) since they are restorable even after drying, they can be compressed in a dry state to attain a reduction in transportation cost, and that (7) since merely adding the particles as they are to drainage results in spontaneous adhesion of a microorganism thereto, microorganism immobilization is easy.

Description

 Description: Sponge-like porous spherical particles and method for producing the same

 The present invention relates to sponge-like porous spherical particles and a method for producing the same. More specifically, in particular, as a carrier for immobilizing microorganisms, a sponge-like porous spherical particle having a polyvinyl acetal skeleton excellent in strength and handling properties, a method for producing the same, and a microorganism immobilization comprising a sponge-like porous spherical particle And a method for treating wastewater. Background art

 Attempts have been made to use enzymes or microorganisms immobilized on a carrier, fill the reactor, and use them as a so-called bioreactor for the production of various useful substances or for wastewater treatment. Examples of the type of bioreactor using immobilized microorganisms include a fixed bed type in which microorganisms are immobilized in a reaction tank and a fluidized bed type in which immobilized microorganisms are used while flowing. In wastewater treatment, a fluidized bed type is used especially for the purpose of denitrification.

As a carrier for immobilized microorganisms used in the fluidized bed type, a carrier having a low specific gravity and easy to flow is desired. Therefore, an organic polymer carrier is generally used rather than an inorganic carrier. Examples of the organic polymer carrier include a gel carrier such as polyvinyl alcohol, acrylamide, and polyethylene glycol, and a porous body such as polyethylene, polyurethane, polyvinylidene chloride, and cellulose. However, although gel-like carriers have good affinity for microorganisms, they generally have poor mechanical strength (abrasion resistance). It is inferior, and is susceptible to wear due to friction between carriers in a fluidized bed and friction with the inner wall of the reaction tank, and has the disadvantage that the carrier life is short. In addition, the porous body has a problem that the weather resistance is low, and cellulose itself is susceptible to biodegradation, the carrier is easily broken down over a long period of use, and the life is short.

 Among the above organic polymer gel carriers, polyvinyl alcohol (hereinafter referred to as polyvinyl alcohol)

Gels are used as a carrier for wastewater treatment because they have excellent hydrophilicity and fluidity. However, as described above, PVA gel does not have sufficient mechanical strength and its productivity is not high. Therefore, in order to increase the mechanical strength of the PVA gel-like carrier and further increase the productivity, attempts have been made to make the PVA gel into a spherical shape or formally. For example, Japanese Patent Application Laid-Open No. 7-41516 discloses that a mixture of PVA and alginic acid is dropped into a calcium chloride solution, molded into a spherical shape, and then formalized with formaldehyde to form a spherical polyvinyl formal (hereinafter, referred to as "formal"). A method for obtaining a gel is disclosed. In addition, Japanese Patent Application Laid-Open No. 9-1124731 describes that spherical gel particles are obtained by the same method as in Japanese Patent Application Laid-Open No. 7-141516, which is frozen and thawed to form a network structure. The invention discloses a spherical gel particle having the same. This gel is formalized while suppressing the swelling of the gel by adding sodium sulfate.The degree of formalization is about 30%, and the network structure is small, so the gel itself has low elasticity and is dried. In such cases, it is considered brittle and easily collapsed. Therefore, although the mechanical strength is improved, it cannot be dried, and it must be transported in a water-containing state, resulting in a disadvantage that the transportation cost is high.

It is considered that there is no large opening on the surface of the PVF spheroidized by the above method. Therefore, although the above PVA spherical particles have improved strength, even if they have openings, the openings are considered to be small, so that the adhesion of microorganisms is limited to the surface, and the adhesion of microorganisms is limited. Ten The disadvantage of not being a minute is not eliminated. Disclosure of the invention

 An object of the present invention is to solve the above-described problems of gel particles having a skeleton of polyvinyl acetal resin. The present invention solves the problem of the gel-like polyvinyl acetal spherical resin by making the polyvinyl acetate resin into a sponge shape. According to the present invention, (1) not only the surface has an opening of an appropriate size but also a hole communicating with the opening, so that the inside of the hole is a microorganism and a medium.

(Or wastewater) can move freely. (2) As a result of having pores of an appropriate size, microorganisms can adhere not only on the surface but also inside the communication holes, for example, the efficiency of wastewater treatment greatly increases. (3) It has high porosity and has low apparent specific gravity, so it is easy to flow. (4) Despite high porosity, it has excellent mechanical strength (wear resistance) and elasticity. (5) Even when dried, it has high mechanical strength, so it can be compressed and can greatly reduce the transportation cost. (6) After drying, it is hydrated and returns to its original state, and the strength of the original hydrogel (7) Microorganisms spontaneously attach to (or bind to, or aggregate with) spherical particles by simply pouring wet or dry spherical particles into wastewater as they are, with sponge-like elasticity and high porosity. Have the very good property of doing Achieve the effects, Poribiniruase evening spongy spherical particles you a Ichiru resin as a skeleton and a method for producing the same.

The present invention includes “a hydrous sponge-like porous spherical particle having a skeleton of a polyvinyl acetal resin having at least one opening and a communicating hole connected to the opening” (hereinafter, simply referred to as a “hydrous sponge-like spherical particle of the present invention”) or “Spherical particles” are suitable for fluidized bed bioreactors, especially for wastewater treatment. And due to its characteristics, it can be used for hydroponic cultivation of crops. It is suitably used as a solution holding material, a plant support material, a carrier for immobilizing animal and plant cells, artificial water, a soil improvement material, a pipe cleaning member, a filtering material, a water absorbing material, and the like. It can also be used as a submersible fluid cleaning member or a submersible fluid massage member. In the underwater fluidized washing, spherical particles and an object to be washed (for example, vegetables) are put into water, bubbles are generated from the bottom of the water tank, and the entire object is published. This is a method of cleaning an object to be cleaned. This method is suitable for washing delicate vegetables or vegetables with many irregularities. Underwater fluidized massage is a method of stimulating the skin and obtaining a massage effect by bringing spherical particles into contact with the human body while flowing in a water tank such as a bathtub.

 The present invention relates to a water-containing sponge-like porous spherical particle having a skeleton of polyvinyl acetate resin and having at least one opening and an internal communicating hole connected to the opening.

 In a preferred embodiment, the polyvinyl acetal is polyvinyl formal. In a preferred embodiment, the opening has an average pore diameter of about 1 to 50. In a preferred embodiment, the water contained in the communication vent is easily replaced with air.

 Further, in a preferred embodiment, the internal pores have an average pore diameter of 40 to 100 m and an average porosity of 50 to 98%. In a preferred embodiment, the degree of acetalization is 50 to 85 mol%, and in a preferred embodiment, the apparent specific gravity is 1.00 to 1.20.

Further, the present invention provides a dry sponge-like porous spherical particle which, when swollen, forms a sponge-like porous spherical particle having a skeleton of a polyvinyl acetal resin having at least one opening and an internal communicating hole connected to the opening. About. In a preferred embodiment, the polyvinyl acetal is polyvinyl formal. In a preferred embodiment, the dried sponge-like spherical particles have an average pore diameter of about 1 to 50 / im when swollen. In a preferred embodiment, the water contained in the communication vent is easily replaced with air.

 Further, in a preferred embodiment, when the dried sponge-like spherical particles are swollen, the average pore diameter of the internal communicating pores is 40 to 100 xm, and the average porosity is 50 to 98. %. In a preferred embodiment, the degree of acetalization is from 50 to 85 mol%, and in a preferred embodiment, the apparent specific gravity in a water-containing state is from 1.0 to 1.2. It is 0.

 Further, the present invention provides the following steps:

 (1) a step of obtaining a spherical polyvinyl alcohol molded product by dropping a mixture of polyvinyl alcohol, a high molecular polysaccharide capable of gelling with a cation, and a pore-forming agent into a solution containing a cation; and

 (2) a step of acetalizing the obtained spherical polyvinyl alcohol molded product; and a method of producing water-containing sponge-like porous spherical particles. Further, the present invention provides the following steps:

 (1) a step of obtaining a spherical polyvinyl alcohol molded product by dropping a mixture of a polyvinyl alcohol, a polysaccharide capable of gelling with a cation and a pore-forming agent into a solution containing a cation;

 (2) a step of acetalizing the obtained spherical polyvinyl alcohol molded product to obtain hydrous sponge-like porous spherical particles; and

 And (3) a step of drying the obtained water-containing sponge-like porous spherical particles.

In a preferred embodiment, in the above two methods, the pore-forming agent is It is a pore-forming agent that can swell at a high temperature, and the temperature of the cation-containing solution is a temperature equal to or higher than the temperature at which the pore agent swells. In a preferred embodiment, the pore-forming agent is a starch.

 In a preferred embodiment, in the above two methods, the high molecular weight polysaccharide is alginic acid or a salt thereof, and the cation is calcium ion.

 Further, in a preferred embodiment, in the above two methods, the -acetalization is performed with formaldehyde.

 In a preferred embodiment, the drying step includes a step of pressing the sponge-like porous spherical particles.

 Further, the present invention provides a hydrous sponge-like porous spherical particle, comprising the following steps:

 (1) a step of obtaining a spherical polyvinyl alcohol molded product by dropping a mixed solution of polyvinyl alcohol, a polysaccharide capable of gelling with cations, and a pore-forming agent into a solution containing cations;

 (2) a step of subjecting the obtained spherical polyvinyl alcohol molded product to an acylation step. In a preferred embodiment of the water-containing sponge-like porous spherical particles obtained by a method comprising the steps of: It is a pore-forming agent that can swell at a high temperature, and the temperature of the cation-containing solution is equal to or higher than the temperature at which the pore-forming agent swells.

 Furthermore, the present invention provides a dry sponge-like porous spherical particle, comprising the following steps:

(1) a step of obtaining a spherical polyvinyl alcohol molded product by dropping a mixture of a polyvinyl alcohol, a polysaccharide capable of gelling with a cation and a pore-forming agent into a solution containing a cation; (2) a step of subjecting the obtained spherical polyvinyl alcohol molded product to an acylation process to obtain water-containing sponge-like porous spherical particles;

 (3) a step of drying the obtained water-containing sponge-like porous spherical particles.

 In a preferred embodiment, the pore-forming agent is a pore-forming agent capable of swelling at a high temperature, and the temperature of the cation-containing solution is equal to or higher than the temperature at which the pore-forming agent swells.

In a preferred embodiment, it is a dried sponge-like porous spherical particle obtained through a pressing step after the drying step.

 Further, the present invention provides the following steps:

 (1) a step of extruding a mixed solution of polyvinyl alcohol, a polysaccharide capable of gelling with a cation, and a pore-forming agent into a solution containing a cation with a nozzle to obtain a string-shaped polyvinyl alcohol molded product; and

 (2) a step of subjecting the obtained string-like polyvinyl alcohol molded article to an acylation to obtain a string-like water-containing sponge-like porous polyvinyl acetal; And a method for producing acetal.

 Furthermore, the present invention provides: (1) a method of extruding a mixed solution of polyvinyl alcohol, a polysaccharide capable of gelling with a cation and a pore-forming agent by a nozzle into a solution containing a cation, and forming a string-shaped polyvinyl alcohol. Obtaining a product;

 (2) acetalizing the obtained string-like polyvinyl alcohol molded product to obtain a string-like water-containing sponge-like porous polyvinyl acetate;

(3) drying the obtained water-containing sponge-like porous polyvinyl acetal; The present invention relates to a method for producing a cord-like or granular dry sponge-like porous polyvinyl acetal.

 Furthermore, the present invention relates to a carrier for immobilizing microorganisms, comprising a water-containing sponge-like porous spherical particle, a dry sponge-like porous spherical particle, a string-like or granular water-containing or dry sponge-like porous polyvinyl acetal.

 And the present invention relates to a method for treating wastewater, comprising a step of adding the microorganism-immobilizing carrier to wastewater. BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the present invention will be described in detail.

 The present invention relates to a sponge-like spherical particle having a skeleton of polyvinyl acetal, which has at least one opening and an internal communicating hole connected to the opening. First, in the present invention, "sponge-like" means that the material has pores having a large pore diameter, such as a so-called synthetic sponge, and has elasticity that returns to its original state even when compressed. Mean different concepts.

 In general, gel is broadly defined as: (1) a state containing a large amount of water and in a uniformly dispersed state (eg, agar, konjac, jelly, etc.); and (2) low water and a void It is defined as having a network structure (eg, silica gel). In consideration of the content of the hydrogel molded article described in the above-mentioned Japanese Patent Application Laid-Open No. 7-41515 or Japanese Patent Application Laid-Open No. 9-124773, it is not (2) but (1) ) Is considered to be a gel.

By the way, both the hydrous sponge and the hydrous gel have a large number of pores and water filled in the pores. Generally, in the case of gel, these pores are as fine as several microns from the molecular level, and in sponge, they often refer to larger diameters. However, the pore size alone does not make a clear distinction. Water can easily flow out of this hole without any special operation, and Sponge is the one that can be restored to its original size by being replaced by air, and gel that can not be restored. Here, “water can easily flow out” means that the water flows out when deformed by applying external pressure. For example, spongy materials used for dishwashing, car washing, etc. are deformed by external pressure, the water held in the internal holes is squeezed out, and air instead of water flows into the internal holes. The sponge is a sponge because it can be made to be able to be removed.On the other hand, the jelly-like material such as the agar and the konjac is not able to squeeze out the water held in the internal hole even when external pressure is applied. On the other hand, air cannot flow into the holes instead of water, so it can be called a “gel”.

 As a means for removing water without changing the external pressure, there is a drying means. This means is to remove the water inside the hole by heating or the like. When the gel is dried, the volume shrinks significantly, probably due to the surface tension of the water. The surface tension increases as the pore size decreases. Then, when water (liquid) contained in the fine pores is directly vaporized at normal temperature and normal pressure, the surface tension of the water acts in the pores, so that the fine morphology of the pores is significantly impaired and crushed. Probably because of the state. On the other hand, the sponge has the high strength of the skeleton itself that forms the pores even if the same force acts on the surface tension, and can resist this surface tension, so that the shape of the pores is maintained and the volume shrinkage is suppressed. In the case of PVF, the higher the degree of formalization, the higher the skeletal strength.

As described above, there are differences between sponge and gel, such as different pore size, different deformation due to external pressure, and different behavior during drying. In the case of PVF, the smaller the pore size and the lower the degree of formalization, the stronger the properties as a gel. For example, in the case of PVF with an average pore diameter of about 60 // m, those with a degree of gasification of about 30% or more are sponge-like. Those less than this are gel-like. On the other hand, the average pore diameter is about

The degree of PVF does not become sponge unless the degree of assembling is 50% or more.

 The term “spherical” includes not only a true sphere but also a slightly deformed spherical shape, for example, an egg shape.

 In the present invention, the “opening and the internal communicating hole connected to the opening” means that one opening on the particle surface and the pore connected to the opening are connected inside to form a hollow shape (hollow shape). means.

 The average pore size of the openings of the sponge-like spherical particles of the present invention is about 1 to about 50 m, preferably 5 to 20 wm. The opening communicates with the internal pores. Therefore, the size and structure of the pores of the present invention are different from the network structure at the molecular level, which is usually considered. Therefore, the sponge-like spherical particles of the present invention are different from a mere gel having a network structure. In addition, the size of the pores is such that water and air can move freely.For example, in wastewater treatment, nutrients necessary for the growth of microorganisms and substances to be treated can move freely. The effect is that microorganisms proliferate and pollutants are quickly removed. Therefore, if the average pore size of the opening is smaller than about m, although the microorganisms will adhere, the movement of the substance may be hindered. If it is larger than about 50 / xm, a problem of sponge strength may occur in relation to the porosity.

 The average pore diameter of the internal continuous vent and the pore diameter of the opening can be measured by, for example, a mercury intrusion method using a porosimeter manufactured by POROUS MATERIAL S, INC based on ASTM (Designation: D4404-84).

The average porosity of the sponge-like spherical particles of the present invention in a water-containing state is preferably about 50 to 98%, more preferably about 70 to 95%, and most preferably about 85 to 93%. is there. If the porosity is less than about 50%, open cells When the porosity exceeds about 98%, the mechanical strength such as abrasion resistance of the particles is reduced, and there may be a problem that the use is restricted depending on the use.

 The average porosity is obtained by measuring the apparent volume (V a) and the true volume (V), and is obtained by the formula: ε = (1−V / V a) × 100 (%). The apparent volume (V a) is obtained, for example, as an average value of the diameter of a sample in a water-containing state measured at three points using calipers. The true volume (V) is measured using, for example, Shimadzu Dry Type Automatic Densitometer Acubic 133 (trade name).

 In the present invention, “having a polyvinyl acetal resin as a skeleton” means that the polyvinyl acetal resin maintains a spherical shape. Therefore, it means that all of the hydroxyl groups of the polyvinyl alcohol do not need to be converted into polyvinyl acetal, that is, the degree of acetylation need not be 100%.

The degree of acylation of the sponge-like spherical particles of the present invention is preferably about 50 to 85 mol%. More preferably, it is about 50-75 mol%, and still more preferably, it is 55-70 mol%. When the degree of acetalization is less than 50 mol%, the degree of molecular crosslinking is low, and therefore, the strength is not sufficient and the fastness to friction is low. Therefore, particularly when used as a fluidized bed type carrier, the carrier tends to be worn due to friction between the carriers and friction with the inner wall of the reaction tank, and the life of the carrier is shortened. If the degree of caseilation exceeds 85 mol%, the porosity decreases, the apparent specific gravity increases, and the water content decreases. Therefore, when it is used as a fluidized bed type carrier, it tends to settle down (is difficult to float), and the fluidity in the treatment tank is reduced. Furthermore, the decrease in the amount of hydroxyl groups in the spherical particles is not preferable because the hydrophilicity of the spherical particles is reduced. In addition, the rebound resilience when hydrated becomes low, which is not preferable. In particular, when forming dry spherical particles, In this case, it is difficult to restore the original shape.

 The degree of acylation can be determined by the following equation from measurement of proton NMR in deuterium chloroform and aqueous solution of trifluoroacetic acid.

 Case F = (a / c) X 100 (%)

 a represents the sum of the peak intensities of the methylene protons adjacent to the ether group (for example, 4.667, 5.150, 5.313, and 5.326 ppm), and c represents Represents the sum of the peak intensities of the methine protons (eg, 4.153, 4.44'2 ppm).

 The apparent specific gravity of the sponge-like spherical particles of the present invention in a water-containing state is preferably about 1.00 to 1.20 in order to exhibit good fluidity. Preferably, it is from 1.00 to 1.05. When the apparent specific gravity is smaller than 1.0, the carrier only floats even when used in a fluidized bed type, and lacks fluidity. For example, it becomes difficult to treat wastewater. When the apparent specific gravity exceeds 1.20, sedimentation is likely to occur, and also in this case, fluidity is lacking.

The apparent specific gravity in a water-containing state was determined by the following formula. Apparent specific gravity D ₂ in wet condition. = (W / V) X (S _T / S ₂₀ )

D _2. = Completely hydrous polyvinyl acetate at a water temperature of 20 ° C

 Specific gravity of porous spherical particles (gZm l)

 W: Polyvinyl acetal in water condition at T ° C

 Weight of porous spherical particles (g)

 V: Polyvinyl acetal in a completely hydrated state at water temperature T ° C

 Volume of porous spherical particles (m 1)

S _τ : Specific gravity of distilled water at water temperature T ° C (gZm l)

S _2. : Specific gravity of distilled water at a water temperature of 20 ° C (gZm 1) The sponge-like porous spherical particles of the present invention preferably have a size in a water-containing state of about 1 mm to 20 mm. Particles of this size have good fluidity and can exert their treatment capacity in wastewater treatment and the like. If the particle size exceeds about 2 O mm, not only the fluidity of the particles will decrease, but also the effective surface area will decrease, making it difficult to maintain a high concentration of microorganisms and reducing the processing capacity. . If the particle size is smaller than 1 mm, the recovery filter may be clogged when used in a sewage treatment device with a recovery filter installed at the outlet. The size of the sponge-like spherical particles of the present invention can be arbitrarily adjusted as described later.

The dry sponge-like porous spherical particles obtained by removing water from the water-containing sponge-like porous spherical particles of the present invention (hereinafter, referred to as “dry sponge-like porous spherical particles”) have sponge-like elasticity. As a result, the resilience is excellent. This is also a major difference from conventional gels. That is, the dried sponge-like porous spherical particles of the present invention swell when brought into a water-containing state, and when swelled, have a skeleton of a polyvinyl acetal resin having at least one opening and a communicating hole connected thereto. Form porous spherical particles. The dried sponge-like porous spherical particles of the present invention have an appropriate hydroxyl group to facilitate the absorption of moisture, and after swelling, have the opening, average pore diameter, It has characteristics such as apparent specific gravity in a water-containing state. Needless to say, the dried sponge-like porous spherical particles include compressed dry sponge-like porous spherical particles obtained by drying and then compressing. The sponge-like porous spherical particles of the present invention having the above characteristics have the following features. (1) Since not only the surface has an opening of an appropriate size but also a hole communicating with this opening, the inside of the hole contains microorganisms. And (2) have moderately sized pores so that microorganisms can be removed from the surface. And can also adhere to communication holes, for example, greatly increasing the efficiency of wastewater treatment

(3) It has high porosity and low apparent specific gravity, so it is easy to flow. (4) Despite high porosity, it has excellent mechanical strength (wear resistance) and elasticity. (5) Even when dried, it has high mechanical strength, so it can be compressed and can greatly reduce the transportation cost. (6) After being dried, it is hydrated and returns to its original state, and the original hydrogel is removed. (7) Microorganisms naturally adhere to (or bind to, or bind to) spherical particles simply by throwing wet or dry spherical particles into wastewater as they are, having high sponge-like elasticity, high porosity. (Aggregation). Therefore, the sponge-like porous spherical particles and the dry sponge-like porous spherical particles of the present invention are extremely excellent as carriers for immobilizing microorganisms.

 Further, the water-containing sponge-like porous spherical particles or the dry sponge-like porous spherical particles of the present invention can be used as a carrier for entrapping and immobilizing depending on the use. Comprehensive immobilization can (1) maintain microorganisms at high concentration and achieve high-speed treatment of wastewater. (2) Immobilize specific microorganisms to process specific substances or recover organic matter. It has the characteristic of taking.

 In order to entrap and immobilize microorganisms on the water-containing sponge-like porous spherical particles or dried sponge-like porous spherical particles of the present invention, for example, a sponge-like porous spherical particle of the present invention is added to a mixed solution containing microorganisms and a microorganism fixing agent. This can be achieved by impregnating the conductive spherical particles or the dried sponge-like porous spherical particles to insolubilize the microorganism immobilizing agent.

Although there is no particular limitation on the microorganism immobilizing agent, sodium alginate is preferably used because it is compatible with the polyvinyl acetate resin used in the present invention and is easy to fill and immobilize. The hydrated or dried sponge-like porous spherical particles of the present invention are mixed with a mixed solution of sodium alginate containing microorganisms. And then reacted with an aqueous solution of a polyvalent metal salt such as an aqueous solution of calcium chloride, and gelled sodium alginate on the surface of the porous spherical particles and / or in the through-holes. Thus, spherical porous particles can be obtained. In order to allow the microorganism immobilizing agent to flow into the communication hole, it is desirable to perform a decompression treatment.

 As described above, the sponge-like porous spherical particles of the present invention can be used as a carrier for an adsorption method (including adhesion, aggregation, biofilm formation, and the like) and an immobilization method, and as a flow-bed / fixed-bed bioreactor. It can also be used as a single carrier. The fluidized bed type bioreactor is particularly suitable for wastewater treatment, etc., and performs not only decomposition of organic substances and the like, but also oxidation reduction such as nitrification denitrification and chemical reactions such as addition, substitution, conversion, and desorption. Can be.

 Further, by applying the method of the present invention, hydrated sponge-like porous particles and dried sponge-like porous particles having a shape other than a spherical shape can be produced. Examples of the form of the particle include a dice (cube) shape, a rectangular shape, and the like. These particles have substantially the same properties, characteristics and effects as the hydrous sponge-like porous spherical particles and the dry sponge-like porous spherical particles of the present invention, and are used in a fluidized-bed bioreactor. Can be Of course, taking advantage of this configuration, it can also be used in fixed-bed bioreactors. Spherical particles can also be produced from these sponge-like porous particles. Next, a method for producing the sponge-like porous spherical particles of the present invention will be described. Its manufacturing method includes

 The following steps:

 (1) a step of obtaining a spherical polyvinyl alcohol molded product by dropping a mixture of polyvinyl alcohol, a high molecular polysaccharide capable of gelling with a cation, and a pore-forming agent into a solution containing a cation; and

(2) Acetalizing the obtained spherical polyvinyl alcohol molded product Step;

 That is, in the method of the present invention, first, a mixed solution of PVA, a polysaccharide capable of gelling with a cation, and a pore-forming agent is prepared. Next, by dropping this mixed solution into a solution containing cations, the high-molecular-weight polysaccharides in the droplets are gelled in a spherical form, thereby producing a polyvinyl alcohol molded product.

 As the PVA, PVA having an average degree of polymerization of 500 to 380 is desirable-. PVA may be completely saponified, partially saponified, or may be a mixture of low-polymerized products. When the average degree of polymerization is less than 500, it is difficult to obtain sponge-like porous spherical particles having a high porosity. The viscosity is too high, which makes handling difficult in the kneading process. Polyvinyl alcohol raw materials having different degrees of polymerization can be blended and used, and the present invention is not limited to the above-mentioned PVA having a degree of polymerization of, for example, PVA having a degree of polymerization of 150 and PVA having a degree of polymerization of 300. May be used in combination.

 The concentration of PVA is not particularly limited, but is generally preferably 5 to 15% by weight, more preferably 7 to 10% by weight, and still more preferably 7 to 9% by weight. If the PVA concentration exceeds 15% by weight, the viscosity of the solution will be too high, making it difficult to handle, as well as the drip-like shape of a thread when it is dropped to form a sphere. Particles are generated, making it difficult to form a true sphere or a spherical particle close to a true sphere. Further, the porosity decreases, and the spherical particles become hard. On the other hand, if the PVA concentration is lower than 5% by weight, the amount of the polyvinyl acetal resin forming the skeleton of the spherical particles is small, and the strength of the spherical particles decreases, which is not preferable.

Polymer polysaccharides that can gel with cations include, for example, alginic acid Water-soluble polysaccharides such as, but not limited to, sodium alginate, carrageenan, and sodium polyacrylate. Sodium alginate is most suitable in consideration of the gelation speed and the state of the gel. The molecular weight of sodium alginate is not particularly limited. However, when high molecular weight sodium alginate is used, the gelation rate is high and neat particles are easily produced. If the molecular weight of sodium alginate is too high, the viscosity when it is made into a solution becomes too high, so that it becomes easy to form droplet-like particles, which is not preferable. For example, sodium alginate having a viscosity of about 30 dPA'sec at a concentration of 20 ° C and a concentration of 4% is preferably used, but is not limited thereto.

 When the concentration of the high molecular weight polysaccharide that can be gelled by the cation is high, the viscosity of the solution increases, which often hinders dripping of the mixed solution. On the other hand, when the concentration is low, the reaction rate of gel formation becomes low, and it becomes difficult to obtain spherical particles. In the case of sodium alginate, it is preferably about 0.3 to 3% by weight, particularly about 0.5 to 1.5% by weight, depending on the molecular weight. If the concentration of sodium alginate is less than 0.3% by weight, the dispersing power becomes stronger than the surface tension of the water-soluble polymer polysaccharide itself on the water surface or in water, and the polymer polysaccharide removes water. It becomes trapped and spreads on water. On the other hand, if the concentration of sodium alginate exceeds about 3% by weight, it is difficult to obtain spherical particles having a uniform diameter as a result of injecting into a solution with a string pulled upon dropping.

The pore-forming agent is not directly involved in the molding of spherical particles, but is removed later to form cavities. As a result, sponge-like porous spherical particles having communication holes are obtained. Since the acetalization reaction is performed under acidic conditions, a pore-forming agent that is dissolved and removed under acidic conditions is suitable for production. Desirably, the pore former is capable of swelling at elevated temperatures. For example, PVA, cation In the mixture with the gelling polymer polysaccharide, the pore-forming agent is in the form of particles, but if it is swollen when molded into a sphere with a cation-containing solution, the space containing the pore-forming agent expands. It becomes continuous, and a communication hole is easily formed. Further, the mixture may be prepared at a temperature at which the pore-forming agent swells, but is preferably not swelled.

 Starch is suitable as such a pore-forming agent. Starches can be of any type. For example, evening starch, corn starch and the like can be mentioned. A suitable starch concentration is about 3 to 8%. If it is higher than about 8%, the formalization reaction rate will be reduced, and the resilience of the formed water-containing sponge-like porous spherical particles will decrease.If it is lower than about 3%, shrinkage during the formalization reaction will occur. There is a problem that the porosity of the formed water-containing sponge-like porous spherical particles is reduced. The reaction temperature is usually preferably 35 ° C or higher. When the pore-forming agent is used after being expanded, the temperature should be equal to or higher than the expansion start temperature. Therefore, it is preferable to study the swelling temperature of the pore-forming agent in advance. For example, evening Pio power starch begins to swell (gelatinize) at about 60 ° C and peaks at about 70 ° C (highest viscosity). At this time, the volume increases about 2 to 10 times. Corn starch starts to swell (gelatinize) at about 75 ° C, peaks at about 88 ° C, and increases in volume by a factor of about 2 to a dozen. Further, the gelatinization temperature can be further reduced by using acetylated starch or the like.

The mixed solution of the PVA, the polysaccharide capable of gelling with cations, and the pore-forming agent can be prepared as follows. First, water is added to PVA so as to have an appropriate concentration, and the mixture is treated at a high temperature, for example, at 12 It: for 30 minutes to obtain an aqueous solution of PVA. If necessary, PVA that has been previously washed with hot water at an appropriate temperature may be used. This PVA solution and high concentration An aqueous solution of a molecular polysaccharide (eg, sodium alginate) and a dispersion of a pore-forming agent (eg, starch) are mixed.

 Next, the obtained mixed liquid is formed into a spherical shape. By dropping this mixed solution from a nozzle having an appropriate diameter into a solution containing cations, the polysaccharide in the mixed solution is gelled and formed into a spherical shape in the cation solution, A polyvinyl alcohol molded product is obtained. The size of the spherical polyvinyl alcohol molded product particles is adjusted by the size of the nozzle. The cation-containing solution used for gelling the high molecular polysaccharide is not particularly limited, but a metal salt solution such as calcium chloride, zinc chloride, and aluminum sulfate is preferably used. The concentration of these metal salts varies slightly depending on the type of metal salt and the temperature of the aqueous solution, but in the case of calcium chloride, it is about 1 to 10 weight.

%. If the concentration is too high, it will react with an acid during the acetalization reaction in a later step to form a salt, which is not preferable.

 In order to make it easier to form the communication pores of the sponge-like porous spherical particles of the present invention and to increase the porosity, it is preferable to set the temperature of the cation solution to a temperature not lower than the temperature at which the pore-forming agent swells. . When starch is used as the pore-forming agent, it is preferable that the temperature be equal to or higher than the temperature at which the inside of the spherical gel rapidly gelatinizes the starch.

 The polyvinyl alcohol molded product obtained by the above reaction is then subjected to acylation to obtain spherical particles having a polyacetal skeleton. First, the obtained molded product is isolated and reacted with an aldehyde under acidic conditions. When a small amount of a polyvalent metal salt such as calcium chloride is added to an acidic aqueous solution, spherical particles having a uniform diameter can be produced without collapsing the spherical particles.

The acidic condition is used to promote the base reaction. For example, inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid, and organic acids such as maleic acid are used. During ~ However, a strong acid is preferred, and a 5 to 25% sulfuric acid solution, preferably a 10 to 20% sulfuric acid solution is used.

 Examples of the aldehyde used for the acylation include an aliphatic or aromatic aldehyde such as formaldehyde, benzaldehyde, acetoaldehyde, butyraldehyde, acrylaldehyde or daryloxal. An acetate that can be easily converted to an aldehyde by a coexisting acid may be used. Formaldehyde is preferably used in consideration of reactivity with PVA, water solubility, price, handleability, strength and resilience of the reaction product, and ease of processing after the reaction.

 The concentration of the aldehyde used in the reaction may be determined in consideration of the desired degree of acetalization, but it is necessary to appropriately select the concentration according to the concentration of the coexisting acid catalyst, the reaction temperature and the reaction time. The higher the aldehyde concentration, the faster the reaction rate, but it is difficult to control the degree of acetalization. In general, the strength of spherical particles having a high degree of acetalization is improved, but if the degree of acetalization is too high, the porosity of the obtained sponge-like porous spherical particles decreases, and the apparent specific gravity increases, and the water content tends to decrease. And the remaining hydroxyl groups decrease, so that the hydrophilicity decreases. Also, the rebound resilience of the particles decreases. The degree of acetalization can be adjusted by adjusting the amount of aldehydes in the reaction solution, the temperature of the reaction solution, and the reaction time. The reaction temperature is usually about 30 ° to 80 ° (preferably, about 60 ° (: to 80 ° C.) During the acetal reaction under the above acidic conditions, sodium sulfate may be added. Sodium sulfate is used to prevent the elution of PVA In the present invention, sodium sulfate is not usually added to increase the pore size as much as possible.

The pore-forming agent, particularly starch, is eluted and removed and washed after the acetal reaction under acidic conditions, so that the opening and the hole communicating with the opening are removed. It is formed.

 Through the above steps, the sponge-like porous spherical particles of the present invention are produced. By adjusting the blending ratio of PVA, a polysaccharide that gels with cations and a pore-forming agent, the diameter of a nozzle into which a mixture of these is dropped, and the degree of acetalization of PVA, a true sphere is obtained. A variety of sponge-like spherical particles having a skeleton of a vinyl acetate resin having a uniform particle size close to that of a single particle can be easily and mass-produced.

 Since the obtained sponge-like porous spherical particles are in a water-containing state and are inconvenient for transportation and the like, they can be dried to obtain dried sponge-like porous spherical particles. Examples of the drying method include normal-pressure heat drying, freeze-dry drying, standing drying, and fluidized drying. The normal-pressure heated fluidized drying method is preferable from the viewpoint of preventing adhesion of sponges or treating ability. After drying, it is preferable to further compress (press). Even if it is compressed in a wet state, it will soon be restored. Therefore, after drying until the water content becomes 10% or less, the spherical particles are pressed, and the gas contained in the porous spherical particles is extruded and compressed. When the dried sponge-like porous spherical particles obtained by compression are put into water, they quickly absorb water, restore their original shape and size, and can immediately flow. On the other hand, the sponge-like porous spherical particles that are dried without being compressed are difficult for the taken-in air to separate, remain floating on the water surface, and take time until they can be flown. In addition, by compressing and drying, the water content becomes 10% by weight or less, the volume and weight of the porous body can be significantly reduced, and the transportation cost can be remarkably reduced.

The higher the compression ratio, the better, and preferably 1/2 to 1 Z10. Compressed particles compressed to 1/2 to 1/10 swell quickly to 2 to 10 times when injected into water, and restore their original size and shape. When the water-containing sponge-like porous particles and the dry sponge-like porous particles of the present invention are added to wastewater as they are, microorganisms adhere to the surface of these particles, and wastewater is efficiently treated. In this case, it is more effective to use the pressed dry sponge-like porous spherical particles because the microorganisms can quickly penetrate and immobilize inside the particles.

 As described above, the water-containing and dry porous spherical particles of the present invention have been described. However, the water-containing or dry sponge-like porous polyvinyl acetal having a shape other than the spherical shape obtained by applying the method of the present invention is PVA, positive PVA. Production is also performed using substantially the same method as the above-mentioned spherical particles, except that a mixture of a high-molecular-weight polysaccharide and a pore-forming agent that can be gelled by ions is contacted with a solution containing a cation without being dropped. Is done.

 For example, the above mixture is directly injected into a cation-containing solution without dripping from a nozzle with a circular, rectangular, or square injection port, so that the cut end has a cylindrical or square shape. It is formed into a string and then acetalized, and the obtained water-containing sponge-like porous polyvinyl acetal is cut to obtain water-containing sponge-like porous polyvinyl acetate particles. Further, after drying, it may be spherical.

 Further, the obtained water-containing sponge-like porous particles can be dried and compressed to obtain dried sponge-like porous particles. Alternatively, the hydrated sponge-like porous resin may be dried and compressed, and then cut. The dried sponge-like porous resin has appropriate elasticity and can be cut without losing its shape. After cutting, the corners may be sharpened to make them spherical. The string-like water-containing sponge-like porous polyvinyl acetal thus obtained can be used as it is as a fixed-bed type bioreactor, and these granular materials are used as a fluidized-bed type bioreactor. Used.

Hereinafter, the present invention will be described with reference to examples. It is needless to say that the present invention is not limited to this. The pore diameter, porosity and degree of acetalization were measured based on the above-mentioned methods, and% in the following Examples and Comparative Examples means% by weight.

 (Example 1: Production of water-containing sponge-like porous spherical particles)

 A completely saponified PVA resin having an average degree of polymerization of 1500 was dissolved in hot water and then cooled. Separately, prepare an aqueous solution of sodium alginate and an aqueous dispersion of evening Pio power starch, and finally reach a concentration of 8.0% PVA, 1.0% 'alginic acid and 6% evening Pio power starch. These solutions were mixed as described. The temperature of the mixture was 40 ° C. The mixture is extruded from a nozzle with a diameter of 4 mm to form droplets, and the droplets are slowly dripped into 5000 ml of a 3% aqueous solution of hydrochloric acid at 70 ° C. At the same time as the starch began to solidify, the starch gelatinized, and after about 15 minutes, colorless and translucent spherical particles were formed. The obtained spherical particles were added to an aqueous solution of 10.0% formaldehyde and 15.0% sulfuric acid at 70 ° C. and reacted for about 15 minutes to obtain white spherical particles. The obtained white spherical particles were alternately repeatedly compressed and opened in water, and washed with water to remove starch, alginic acid, and unreacted acid and formaldehyde. The particle diameter of the spherical particles thus obtained was about 4 to 5 mm, close to a true sphere, sponge-like, and was rich in flexibility and elasticity.

The obtained spherical particles were dried by t-butyl alcohol freeze-drying method, and a scanning electron micrograph of the inside of the particles was taken and observed. The spherical particles were porous bodies having a large number of communication holes inside a sponge-like interior. The size of the opening was about 5 to 30 / m, with an average of about 10m. The size of the communication hole was about 30 to 100111, with an average of about 60 m. Further, the obtained particles had an acetalization degree of about 80%, an average porosity of 90%, and an apparent specific gravity in a water-containing state of 1.04. When the spherical particles of the obtained porous body were dried at 60 ° C. and normal pressure, the volume thereof hardly changed. The size of the opening was about 5 to 30 m, averaged about 10 m, and the size of the communication hole was about 20 to 100 m, averaged about 50 m. The average porosity was 90%.

 (Comparative Example 1)

 White spherical particles were obtained in the same manner as in Example 1 except that the acetalization reaction was performed at 50 ° C. without adding a pore-forming agent. The degree of acetalization of the white spherical particles was about 40%, and the apparent specific gravity in a water-containing state was 1.05.

 When the obtained white spherical particles were dried at 60 ° C. and normal pressure, the volume shrank significantly, and the size of the opening could not be measured.

 (Example 2)

 White spherical particles were obtained in the same manner as in Example 1 except that corn starch was used as a pore-forming agent at 7.5% and corn starch was reacted at 75 ° C. In this example, the pore-forming agent corn starch swelled during the acetalization reaction.

 The pore size of the obtained spherical particles was about 20 to 80 / m, and the average was about δθ ^ ιη. The obtained particles had an acetalization degree of about 65%, a porosity of about 85%, and an apparent specific gravity in a water-containing state of about 1.05.

 (Example 3)

Example 1 was repeated except that PVA was 7.5%, corn starch was 5% as a pore-forming agent, the temperature of a 3% calcium chloride aqueous solution was 60 ° C, and the acetalization reaction was performed at 60 ° C for 30 minutes. In the same manner as in the above, white spherical particles were obtained. In this experiment, corn starch, a foam-forming agent, did not swell during the acetalization reaction. The pore size of the obtained spherical particles was about 5 to 20 / im, and the average was about 15 / im. The obtained particles had a degree of acetalization of about 67%, a porosity of about 75%, and an apparent specific gravity in a water-containing state of about 1.07.

(Example 4: Production of dry sponge-like porous spherical particles)

Next, the sponge-like porous spherical particles having a diameter of about 4 mm obtained in Example 1 were dried at 60 ° C for 1 hour. The water content was 3.0%. When this was pressed at a pressure of 1-0.07 × 10 ⁷ NZm ² , it was compressed into a disk with a thickness of about 0.75-1.5 mm. Twenty compressed samples were put into water and shaken. They quickly absorbed water and swollen, and sank below the surface in 8 seconds. The sinking particles were removed and measured in a wet state with a water content of 50%, and all were restored to the size and shape (spherical) before compression. The size of the opening, the size of the internal communication hole, and the average porosity were also equal to those before compression.

 The water content was determined by the following equation.

 Moisture content = (1-1 W2 / W 1) X I 00 (%)

 W 1 = weight of wet sponge

 W 2 = Weight of dry sponge (Weight of water-containing sponge after drying at 105 ° C for 2 hours)

 In contrast, 20 samples that were dried but not compressed were placed in water and shaken, and all particles floated on the water surface. Although the surface of the particles was absorbing water, the air inside the particles did not escape, and thus remained floating even after 2 hours.

 (Example 5: Durability test 1)

As a simulation test assuming the flow in the bioreactor, a container with a diameter of 150 mm and a height of 400 mm When the sponge-like porous spherical particles of Example 1 were added and flowed with aeration, the spherical particles were uniformly dispersed and flowed. This aeration and flow

It was carried out continuously for one month, and the particles were taken out and observed. These particles did not show any wear or breakage due to friction, and were confirmed to be rich in wear resistance. The polyurethane sponge, cellulose sponge, and calcium alginate spherical gel used for comparison were worn. The gel-like spherical particles obtained in the comparative example also exhibited abrasion, but not as much as the polyurethane sponge, the cellulose sponge, and the calcium alginate spherical gel.

 (Example 6: Durability test 1 2)

 A water-resistant sandpaper (100th count) was stuck to the inner surface of the side wall of the container similar to that in Example 4, and the stirring blade was rotated at a speed of 300 rpm to mechanically flow the particles, thereby forming the particles and the inner wall. It was set so that friction occurred between. The same amount of sponge-like porous spherical particles of Example 1, a commercially available polyurethane sponge having a diameter of 3 mm, a commercially available cellulose sponge, and a commercially available cellulose sponge and calcium alginate spherical gel of the same amount as in Example 4 were added to each container, and stirred. Flow was performed. The polyurethane sponge, the cellulose sponge, and the calcium alginate spherical gel were all confirmed to have their surfaces scraped and worn after 24 hours, but the sponge-like porous spherical particles of the present invention were found after one week. No wear due to friction was observed at all, and it was confirmed that the steel had excellent wear resistance. The calcium alginate gel was prepared by drop-solidifying a 1% aqueous sodium alginate solution into a 2% aqueous calcium chloride solution.

 (Example 7: Microbial degradation test of sponge-like porous spherical particles)

The sponge-like porous spherical particles obtained in Example 1 were filled to about 10% of the volume of a polypropylene container having a size of 2 mm and having many holes. The entire container was immersed in an activated sludge aeration tank. Six months later, the container was taken out, and the sponge-like porous spherical particles in the container were observed.Aerobic microorganisms adhered to the surface of the sponge-like porous spherical particles at a high density. No erosion of the particles was observed.

 (Example 8: Production of inclusive immobilized microorganism)

 A mixture of activated sludge concentrated to about 50 g / liter by centrifugation and 2% sodium alginate at a volume ratio of 1: 1 was prepared, and this was obtained in Example 1. The resulting sponge-like porous spherical particle carrier was impregnated. The mixed solution was introduced under reduced pressure to increase the amount of impregnation, and a spherical particle carrier impregnated with microorganisms was obtained.

 The obtained spherical particle carrier was further added to a 5% calcium chloride aqueous solution, stirred, and reacted for about 3 hours. As a result, sodium alginate in the spherical particle carrier was insolubilized, and the microorganisms were included and immobilized.

 The same spherical carrier having the entrapped and immobilized microorganisms was filled in the same container as in Example 4 with the same amount as in Example 4, and allowed to flow while being aerated.The spherical particles were uniformly dispersed and flowed. did. After one month of continuous flow, the particles were taken out and observed. No wear or breakage due to friction was observed, and it was confirmed that the particles had high wear resistance. In addition, the porous spherical particles did not undergo any erosion degradation by microorganisms, confirming that the life of the spherical particles as a carrier was long. Industrial applicability

According to the present invention, (1) not only a surface has an opening of an appropriate size but also a hole communicating with the opening, so that microorganisms and a culture medium (or wastewater) can move freely in the hole. 2) As a result of having pores of an appropriate size, microorganisms can adhere not only on the surface but also inside the communication holes. (3) High porosity, low apparent density and easy to flow, (4) Despite high porosity, low mechanical strength (wear resistance) (5) It has high mechanical strength even when dried, so it can be compressed and can greatly reduce the transportation cost.

(6) After drying, it is hydrated and returns to its original state, and has the strength, sponge-like elasticity, and high porosity of the original hydrogel, and (7) hydrated or dried spherical particles as waste water Sponge-shaped spherical particles having a skeleton of polyvinyl acetate resin, which has an extremely excellent property that microorganisms naturally adhere to (or bind to or aggregate with) spherical particles simply by being introduced, and exhibit excellent effects. A manufacturing method is provided.

Claims

Scope of the claim 1. Hydrous sponge-like porous spherical particles having a skeleton of polyvinyl acetal resin and having at least one opening and an internal communicating hole connected to the opening. 2. The hydrous sponge-like porous spherical particles according to claim 1, wherein the polyvinyl acetal is polyvinyl formal.  3. The hydrous sponge-like porous spherical particles according to claim 1 or 2, wherein the opening has an average pore diameter of 1 to 50 m.  4. The water-containing sponge-like porous spherical particles according to any one of claims 1 to 3, wherein water contained in the interconnected pores is easily replaced with air. 5. The method according to any one of claims 1 to 4, wherein the internal pores have an average pore diameter of 40 to 100 zm and an average porosity of 50 to 98%. Hydrous sponge-like porous spherical particles.  6. The hydrous sponge-like porous spherical particles according to any one of claims 1 to 5, wherein the degree of acylation is 50 to 85 mol%.  7. The water-containing sponge-like porous spherical particle according to any one of claims 1 to 6, wherein an apparent specific gravity in a water-containing state is 1.00 to 1.20.  8. Dry sponge-like porous spherical particles which, when swollen, form sponge-like porous spherical particles having a skeleton of a polyvinyl acetal resin having at least one opening and an internal communicating hole connected to the opening. 9. Dry sponge-like porous spherical particles according to claim 8, wherein the polyvinyl acetal is polyvinyl formal. 10. The dry sponge-like porous spherical particles according to claim 8 or 9, wherein when swelled, the opening has an average pore diameter of about 1 to 50 / xm. 1 1. The dry sponge-like porous spherical particles according to any one of claims 8 to 10, wherein water contained in the interconnected pores is easily replaced with air when swollen.  1 2. Any of claims 8 to 11 wherein when swollen, the average pore diameter of the internal continuous pores is 40 to 100 m and the average porosity is 50 to 98%. Dry sponge-like porous spherical particles according to the above item.  13. The dry sponge-like porous spherical particles according to any one of claims 8 to 12, wherein the degree of acetalization is 50 to 85 mol%.  14. The dry sponge-like porous spherical particles according to any one of claims 8 to 13, wherein the apparent specific gravity in a water-containing state is 1.0 to 1.20.  1 5. The following steps:  (1) a step of obtaining a spherical polyvinyl alcohol molded product by dropping a mixed solution of polyvinyl alcohol, a polysaccharide capable of gelling with a cation, and a pore-forming agent into a solution containing a cation; and  (2) a process of acetalizing the obtained spherical polyvinyl alcohol molded product, comprising: a step of producing water-containing sponge-like porous spherical particles.  16. The pore-forming agent is a pore-forming agent capable of swelling at a high temperature, and the temperature of the solution containing a cation is equal to or higher than the temperature at which the pore-forming agent swells. Method.  1 7. The method according to claim 15 or 16, wherein the pore-forming agent is a starch.  1 8. The method according to any one of claims 15 to 17, wherein the high molecular polysaccharide is alginic acid or a salt thereof, and the cation is calcium ion. 1 9. Claim 15 wherein the acetalization is carried out with formaldehyde Or a method according to any one of Items 18 to 18. 20. The following steps:  (1) a step of obtaining a spherical polyvinyl alcohol molded product by dropping a mixture of a polyvinyl alcohol, a polysaccharide capable of gelling with a cation and a pore-forming agent into a solution containing a cation;  (2) a step of acetalizing the obtained spherical polyvinyl alcohol molded product to obtain water-containing sponge-like porous spherical particles; and  (3) a step of drying the obtained water-containing sponge-like porous spherical particles;  21. The pore forming agent according to claim 20, wherein the pore forming agent is a pore forming agent capable of swelling at a high temperature, and the temperature of the solution containing a cation is equal to or higher than the temperature at which the pore forming agent swells. Method.  22. The method according to claim 20 or 21, wherein the pore-forming agent is a starch.  23. The method according to any one of claims 20 to 22, wherein the high molecular polysaccharide is alginic acid or a salt thereof, and the cation is calcium ion.  24. The method according to any one of claims 20 to 23, wherein the acetalization is carried out with formaldehyde.  25. The method according to any one of claims 20 to 24, wherein the step of drying includes a step of pressing the hydrous sponge-like porous spherical particles. 26. Hydrous sponge-like porous spherical particles, comprising the following steps:  (1) a step of obtaining a spherical polyvinyl alcohol molded product by dropping a mixed solution of polyvinyl alcohol, a polysaccharide capable of gelling with cations, and a pore-forming agent into a solution containing cations; (2) Acetalizing the obtained spherical polyvinyl alcohol molded product A water-containing sponge-like porous spherical particle obtained by a method comprising:  27. The pore forming agent according to claim 26, wherein the pore forming agent is a pore forming agent capable of swelling at a high temperature, and the temperature of the solution containing a cation is equal to or higher than the temperature at which the pore forming agent swells. Hydrous sponge-like porous spherical particles. 2 8. Dried sponge-like porous spherical particles comprising the following steps:  (1) a step of obtaining a more spherical polyvinyl alcohol molded article by dropping a mixture of polyvinyl alcohol, a polysaccharide capable of gelling with cations, and a pore-forming agent into a solution containing cations;  (2) a step of subjecting the obtained spherical polyvinyl alcohol molded product to an acylation process to obtain water-containing sponge-like porous spherical particles;  (3) a step of drying the obtained water-containing sponge-like porous spherical particles.  29. The pore forming agent according to claim 28, wherein the pore forming agent is a pore forming agent capable of swelling at a high temperature, and the temperature of the solution containing a cation is equal to or higher than the temperature at which the pore forming agent swells. Dry sponge-like porous spherical particles.  30. Claims obtained through a pressing step after the drying step 29. The dry sponge-like porous spherical particles according to item 28 or 29.  31. From the hydrous sponge-like porous spherical particles according to any one of claims 1 to 7 or the hydrous sponge-like porous spherical particles according to claim 26 or 27. A carrier for immobilizing microorganisms.  32. The dry sponge-like porous spherical particles according to any one of claims 8 to 14 or the drying according to any one of claims 28 to 30. A support for immobilizing microorganisms comprising sponge-like porous spherical particles.  3 3. The following steps: (1) Polyvinyl alcohol, high molecular weight polysaccharides and A step of extruding a mixture of the porogen and the pore-forming agent into a solution containing a cation with a nozzle to obtain a string-shaped polyvinyl alcohol molded product; and  (2) a step of acetalizing the obtained string-like polyvinyl alcohol molded article to obtain a string-like water-containing sponge-like porous polyvinyl acetate emulsion; Manufacturing method. 3 4. The following steps:  (1) a step of extruding a mixed solution of polyvinyl alcohol, a high molecular weight polysaccharide capable of gelling with a cation, and a pore-forming agent with a nozzle into a solution containing a cation to obtain a string-shaped polyvinyl alcohol molded product;  (2) a step of acetalizing the obtained string-like polyvinyl alcohol molded article to obtain a string-like water-containing sponge-like porous polyvinyl acetal; and (3) drying the obtained hydrous sponge-like porous polyvinyl acetate; A method for producing a cord-like or granular dry sponge-like porous polyvinyl acetal, comprising:  35. A method for treating wastewater, comprising the carrier for immobilizing microorganisms according to claim 31 or claim 32, or the method according to claim 33 or claim 3. 5. A method for treating wastewater, comprising a step of adding the water-containing or dried sponge-like porous polyvinyl acetal produced by the method according to claim 4 to the wastewater.