JPH09285287A - Carrier and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carrier useful for immobilizing a microorganism, etc., by dropping a raw material mixture comprising a cement, etc., a silicone, polyvinyl alcohol(PVA) and water into an aqueous solution of boric acid, forming a spherical structure, further taking out the formed spherical structure, forming a vacant part and a continuous hole therein in water and drying the resultant product. SOLUTION: This carrier is obtained by dropping a raw material mixture comprising (A) a cement or a cement-based mineral material consisting essentially of calcium silicate, (B) a silicone, (C) polyvinyl alcohol and (D) water into an aqueous solution of boric acid, forming a spherical structure, taking out the formed spherical structure when the permeation of the aqueous solution of the boric acid reaches to the position corresponding to an outer shell part 1 of the carrier, bringing the taken out spherical structure into contact with water to form a vacant part 3 and a continuous hole 2, thereafter drying the resultant spherical structure having vacant part 3 and storing under a moist condition. The objective carrier has a hollow globoid form having the outer shell part 1 forming a vacant part 3 in the interior thereof and the vacant part 3 is connected through the continuous hole formed in the outer shell part 1 to the exterior.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carrier and a method for producing the same, and more particularly to a carrier useful for immobilizing microorganisms and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a carrier for immobilizing microorganisms,
An attachment type carrier for attaching microorganisms to the surface of the carrier and an entrapping immobilization type carrier for entrapping and fixing the microorganisms with an organic polymer are generally used. As the material of the adherent type carrier, sand, activated carbon, granulated slag, porous ceramics, cellulose foam, polyethylene glycol, polyvinyl alcohol, polypropylene, polyurethane and the like that can form a surface to which microorganisms can adhere are used. The most common shape of the adhesive carrier is a sphere, and in addition, a cubic or a cylindrical carrier is also used. In addition, agar and various gels are used as the comprehensive fixed carrier.

The following properties are generally required for the adhesive carrier. That is, it is non-toxic, has a strength that does not aerate in water, does not disintegrate by stirring, has excellent adhesion to microorganisms, and is inexpensive.

Further, various characteristics corresponding to respective uses are required, and, for example, when the adhesive type carrier is used as a carrier for a fluidized bed, the specific gravity of the carrier is appropriate in order to secure the fluidity of the carrier. You need to control things.

Generally, when the particle size of the carrier is reduced, the fluidity tends to be improved, and a carrier having a small particle size is preferable from the viewpoint of fluidity. On the other hand, when it is necessary to hold the carrier in a certain area (for example, in the reaction tank), it is necessary to prevent the carrier from flowing out by a strainer. A diameter (usually about 2 mm or more) is required for the carrier.

When the material of the adhesive carrier is examined in consideration of both fluidity and separability, when the ceramic material is used and the particle size is 2 mm or more, the separability is good. There is a problem that sufficient fluidity cannot be obtained in aeration and stirring. Therefore, as a material satisfying these characteristics, an organic polymer capable of making the specific gravity of the adhesive carrier close to 1 is preferably used.

[0007]

However, the organic polymer-based adhesive type carrier has a problem that sufficient adhesiveness cannot be obtained depending on the type of microorganism to be attached and the type of reaction utilizing the same. .

For example, when an organic polymer-based adherent carrier is added to a nitrification tank for the purpose of accelerating the nitrification reaction, the adherence of microorganisms to the carrier surface is not sufficient, so that stable treatment capacity can be obtained. At least one month was required after the addition of the carrier.

The nitrifying bacteria involved in the nitrification reaction are 200 μm from the surface of the biofilm formed on the carrier surface toward the center.
It is said to exist in the range up to the thickness, and it is necessary to form a sufficient biofilm in order to secure a stable treatment capacity.

Further, when the biofilm is formed sufficiently thick, a denitrification reaction involving anaerobic microorganisms inside the biofilm can be expected, but with an organic polymer-based carrier, an anaerobic reaction cannot be obtained. In many cases, it was difficult to obtain a biofilm having a practically sufficient thickness, and a denitrification tank different from the nitrification tank was usually required.

The object of the present invention is to satisfy the various properties required for an adherent type carrier, and in particular, it has excellent adhesion of microorganisms, good fluidity and separability, and moreover, a biofilm formed on the carrier. In the above, it becomes possible to provide an adhesive carrier capable of effectively performing both an aerobic reaction and an anaerobic reaction.

[0012]

The present invention for solving the above-mentioned problems includes the following inventions.

A first aspect of the present invention relates to a shape of an adhesive carrier, which comprises a hollow spherical body having an outer shell portion forming a cavity therein, and the cavity and the hollow portion are formed by a communication hole provided in the outer shell portion. It is characterized in that it communicates with the outside of the spherical body.

A second aspect of the present invention relates to a method for producing a spherical carrier having a cavity as described above, which comprises a hollow spherical body having an outer shell portion forming a cavity therein, and a communication hole provided in the outer shell portion. A method for producing a carrier in which the cavity communicates with the outside of the hollow sphere by (a) a cement or cementitious mineral material containing calcium silicate as a main component, silicon, polyvinyl alcohol and water. When the raw material mixture is dropped into an aqueous boric acid solution to form a spherical structure, and (b) the aqueous boric acid solution penetrates to a position corresponding to the outer shell of the carrier, A step of taking out from the acid aqueous solution, (c) a step of contacting the spherical structure taken out from the boric acid aqueous solution with water to form the hollow portion and the communicating hole, and (d) a hollow in which the hollow portion is formed. After drying the Jo structure, characterized in that at the humid environment and a step of obtaining the carrier.

A third aspect of the present invention is a method for biologically treating a nitrogen-containing compound using a spherical carrier having the above-mentioned cavities. The spherical carrier is subjected to anaerobic conditions with microorganisms which carry out a nitrification reaction under aerobic conditions. The method is characterized by carrying out nitrification and denitrification by contacting with a nitrogen-containing compound in a state in which anaerobic microorganisms that carry out denitrification are retained.

According to the present invention, the various properties required of the adherent type carrier are satisfied, and among them, the adherence of microorganisms is excellent, the fluidity and the separability are also good, and moreover, the biofilm formed on the carrier. In the above, it becomes possible to provide an adhesive carrier capable of effectively performing both an aerobic reaction and an anaerobic reaction.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The shape of the hollow spherical carrier of the present invention having the above structure is not limited to a spherical shape having a perfect circle in cross section, and may be any shape having an elliptical shape or a substantially circular shape in cross section. The size (diameter) of the communication hole that communicates the cavity with the outside of the carrier can be appropriately selected according to the application of the carrier and the like. For example, when maintaining an aerobic reaction even in a cavity, it is preferable that the pore size is such that a gas can easily pass even in water. That is, when the pore size is very small, it may be difficult to permeate gas due to the osmotic pressure of the liquid. Also, if the pore size is very large,
It may be difficult to retain the gas as bubbles inside the carrier, and the fluidity of the carrier may decrease. The number of communicating holes is not particularly limited, and the hollow spherical carrier of the present invention may have one or more communicating holes.

Further, when both aerobic reaction and anaerobic reaction are performed, if the diameter of the communicating hole becomes too large, the aqueous solution having a high dissolved oxygen concentration easily abruptly enters the inside of the carrier, and the anaerobic condition is increased. Can be difficult to maintain in the cavity.

Further, if the ratio of the area occupied by the communication holes is increased, the outer surface area of the carrier and the surface area of the inside of the cavity, which are the adhering surfaces of the microorganisms, are reduced. It is necessary to reduce the diameter and the diameter.

In order to ensure good fluidity and effectively carry out both the anaerobic reaction and the aerobic reaction, for example, the communication holes have a diameter of about 1/20 to 1/3 of the diameter of the carrier. It is preferable that the ratio of the area of the communication holes to the outer surface of the carrier is about 0.2 to 12%.

The size of the cavity in the carrier of the present invention is 50% to 50% of the carrier diameter in consideration of mechanical strength and the like.
It is preferably about 80%. Further, as the diameter of the carrier, various sizes can be adopted, but 1.5
About 6 mm is preferable.

The material constituting the spherical carrier of the present invention is not particularly limited as long as desired properties such as adhesion of microorganisms, mechanical strength and fluidity in a liquid medium can be obtained. Above all, the outer shell of the carrier is preferably a porous body having water permeability.

As such a material, a boric acid is applied to a raw material mixture containing cement or cementitious mineral material containing calcium silicate as a main component, silicon, polyvinyl alcohol and water, which is obtained by the method described below. Gelled products are particularly suitable. This gelled product has a silanol group formed in silicon that has reacted with an alkaline component, and has extremely excellent adhesion to microorganisms.
Furthermore, this gelled product is a porous material with good water permeability, and due to good liquid permeability between the inside and outside of the carrier cavity,
Efficient processing becomes possible.

The method for producing a spherical carrier made of this gelled product has the steps (a) to (d) mentioned above.

The cement material containing calcium silicate as a main component used in the preparation of the raw material mixture is a cement material containing calcium silicate as a main component and hardened by hydration. Ordinary cement is generally used. Other cementitious mineral materials can be used as long as they have properties similar to.

Silicon, which is another component of the raw material mixture, can be used in various forms. Considering that mixing with cement and generation of hydrogen gas are required before the cement hardens, For example, 0.2-100 μm
Particles or fine particles having a particle size of the order of magnitude are preferred. Examples of such materials include silicon sludge discharged as waste in the semiconductor industry.

The amount of silicon added to the cement or the cementitious mineral material is, for example, such that sufficient strength is obtained in the carrier finally obtained and the desired carrier specific gravity is obtained in combination with other components. Just add it. Moreover, since silicon serves as a structural material at the same time as the foaming agent, the addition amount can be widely varied from 1% by weight to 70% by weight. In the present invention, for example, a carrier having a specific gravity in the range of 0.4 to 1.5 can be obtained.

When silicon is mixed with cement or a cementitious mineral material and reacted with water, an alkaline component in the cement reacts with silicon to generate hydrogen gas, and a spherical structure including gas bubbles is formed. A body is formed, and a carrier having a small specific gravity and good fluidity, in which the outer shell is made of a porous body, can be obtained. In the carrier of the present invention, by selecting the number and diameter of the communication holes, it is possible to improve the fluidity by improving the floating property of the carrier by guiding the bubbles into the cavity and retaining them therein. Can be

As the polyvinyl alcohol used in the raw material mixture, for example, those having a polymerization degree of 500 to 3000 and a saponification degree of 70% or more can be suitably used. The amount of polyvinyl alcohol added is preferably such that the raw material mixture contains 5 to 15% by weight of polyvinyl alcohol.

The raw material mixture can be prepared, for example, by adding a polyvinyl alcohol aqueous solution to a mixture of cement or a cementitious mineral material and silicon, and mixing them. The concentration of the polyvinyl alcohol aqueous solution at that time is
For example, those of about 10 to 20% by weight can be suitably used.

As the raw material mixture, a mixture of 50 g of a polyvinyl alcohol aqueous solution having a concentration of 10 to 20% by weight, water of 8 to 15 g of cement or cementitious mineral material and 1 to 15 g of silicon to make 50 g as a whole. The following composition: the following composition: 10 to 20% by weight aqueous polyvinyl alcohol solution: 50% by weight Cement or cementitious mineral material: 8 to 15% by weight Silicon: 1 to 15% by weight Water: 20 to 41% by weight % Is preferred.

By dropping the above raw material mixture into an aqueous solution of boric acid, the raw material mixture can be molded into a spherical shape to obtain a spherical structure, and from the surface of this spherical structure toward the center thereof, The gelation of polyvinyl alcohol can be promoted by the monodiol reaction of polyvinyl alcohol and boric acid. The boric acid aqueous solution used here is preferably a saturated boric acid aqueous solution, but is not limited to this as long as the desired spherical structure can be formed.

Although it is possible to form spheres even when only the polyvinyl alcohol aqueous solution is dropped into the boric acid aqueous solution, the strength of the spheres is sufficient because the boric acid aqueous solution penetrates slowly into the formed spheres. Immersion treatment for a long time was required to obtain such a gel body. On the other hand, in the present invention, by adding cement or cementitious mineral material and silicon, it is possible to permeate the aqueous boric acid solution into the spherical raw material mixture (spherical structure) in a short time,
Even if the treatment time is shortened, sufficient strength can be obtained to maintain the spherical shape.

Further, polyvinyl alcohol in the raw material mixture gels even when dried, but by dropping the raw material mixture into an aqueous solution of boric acid and utilizing the surface tension, spherical molding of the raw material mixture is facilitated.

Further, in the spherical structure, hydrogen gas is generated by the reaction between the alkaline component of cement and silicon, and bubbles are formed in the spherical structure. By forming the bubbles in the outer shell portion of the finally obtained carrier, the specific gravity of the outer shell portion can be reduced, and the bubble portion communicates the inside and outside of the outer shell portion. By connecting as described above, the outer shell part can be formed as a water-permeable porous body.

If the time from the preparation of the raw material mixture to the dropping into the boric acid aqueous solution is lengthened, the amount of hydrogen gas generated will increase, the content of bubbles in the spherical structure will increase, and finally it will be formed. The specific gravity of the carrier can be further reduced.

By controlling the contact time between the spherical structure obtained from the raw material mixture and the boric acid aqueous solution, only the surface layer of the spherical structure can be gelled. Therefore, when the contact time corresponding to the desired thickness of the outer shell of the carrier has passed, the spherical structure having the gelled surface layer is taken out from the aqueous boric acid solution and brought into contact with water. By this contact with water, water also enters the inside of the spherical structure. At this time, since the non-gelled portion inside the spherical structure is not in contact with the boric acid aqueous solution, a large amount of unreacted cement or cementitious mineral material and silicon are left, and when water enters here This part becomes strongly alkaline, and hydrogen gas is generated by the reaction between the alkali component derived from cement or the cementitious mineral material and silicon. When the generated amount of this hydrogen gas reaches a sufficient amount to destroy the surface layer portion of the gelled spherical structure, the non-gelled raw material mixture inside the spherical structure is released to the outside together with hydrogen gas, and the spherical structure inside the spherical structure. A cavity is formed, and the destroyed portion of the surface layer portion serves as a communication hole that communicates the cavity with the outside.

The hollow spherical carrier thus obtained can be obtained by removing the spherical structure having cavities from water, drying and placing in a wet environment. Natural drying can be used for this drying treatment, and this drying treatment has the effect of increasing the strength of the polyvinyl alcohol gel, and for treatment in a wet environment, cement or cementitious mineral materials are cured to cure the cement. It also has the effect of increasing strength.

The diameter of the obtained carrier can be adjusted, for example, by the diameter of the nozzle for dropping the raw material mixture.

The spherical carrier having cavities thus obtained has a low manufacturing cost, is inexpensive, and has little toxicity. In addition, the silicon compounded in the raw material mixture reacts with the alkaline component of the cement or cementitious mineral material to generate hydrogen gas, which causes the outer shell of the carrier to become a porous body, allowing water to pass between the inside and outside of the cavity. In addition to good adhesion, the adhesion of microorganisms to the outer surface and the inner surface of the cavity is also better. Moreover, since silanol groups are formed in the silicon that has reacted with the alkaline component, the adhesion of microorganisms is further improved.

In the spherical carrier of the present invention, a sufficiently thick microbial layer can be formed in the cavity to favorably perform the anaerobic reaction, and the spherical carrier is formed on the surface of the microbial layer in the cavity or on the outer surface of the carrier. An aerobic reaction can be favorably carried out in the microbial layer. Therefore, for example, it is suitable for a treatment in which a reaction under aerobic conditions and a reaction under anaerobic conditions, such as a combination of a nitrification reaction and a denitrification reaction, are carried out concurrently with one carrier.

[0042]

EXAMPLES The present invention will now be described in more detail with reference to examples. Example 1 Silicon fine particles (average particle size 0.8 μm) and ordinary cement (trade name: ordinary Portland cement, Tokuyama Soda Co., Ltd.)
(New name; manufactured by Tokuyama Corp.)
The same amount of water as this mixture was added and kneaded well to prepare a kneaded mixture. Further, to this kneaded mixture, the same weight as that of a 15% by weight aqueous solution of polyvinyl alcohol having a degree of polymerization of 2000 and a degree of saponification of 80% was added and kneaded well to obtain a raw material mixture. Drop into a saturated aqueous boric acid solution with a stirrer from a
After being formed into a spherical shape of m, it was left for 3 minutes, taken out from the solution, and naturally dried to obtain a production intermediate. This production intermediate was allowed to stand at room temperature for 1 week, aerated with tap water for 3 days, then taken out and dried again to obtain a spherical carrier having cavities (hereinafter referred to as a pot-shaped carrier). When the average particle size of ten manufactured vase-shaped carriers was measured, the average minor axis was 2.4 mm.
(Short diameter distribution: 2.1 mm to 2.6 mm), average long diameter is 3.2 mm (long diameter distribution: 2.8 mm to 3.6 mm),
One to two communication holes having a diameter of 0.2 mm to 0.5 mm were formed. FIG. 1 shows an example of a cross section including the center of the communication hole of the vase-shaped carrier manufactured.

Comparative Example 1 In the same manner as in Example 1, the raw material mixture was molded into a spherical shape in a saturated boric acid aqueous solution, allowed to stand for 1 day, taken out, and naturally dried. The carrier thus prepared is hereinafter referred to as a control carrier. Observation of the cross section of this control carrier revealed that it had porous marks inside and was porous, but the cavities inside the carrier were small, and the cavities were not in communication with the outside.

Comparative Example 2 Instead of the raw material mixture, a 15% by weight aqueous polyvinyl alcohol solution was dropped into a saturated boric acid aqueous solution in the same manner as in Example 1 to form a spherical shape, which was left for 1 day and then naturally dried. Used as a carrier. This carrier is called a PVA carrier.

Example 2 Activated sludge having nitrification activity was added to a fluidized bed reactor (using a strainer having an opening of 2 mm) having a tank volume of 100 ml shown in FIG. 2 so as to have an MLSS of 500 mg / l. The pot-shaped carrier obtained in Example 1 was added so as to have a volume of 30% of the tank volume. Methanol was added to the inorganic salt solution having the composition shown in Table 1 at a rate of 10 ml / l, and the solution was allowed to flow so that the residence time in the reactor was 8 hours. The reactor was immersed in a constant temperature bath at a temperature of 25 ° C., and the pH of the solution in the reactor was adjusted to 7.5 with an aqueous sodium hydroxide solution.

[0046]

[Table 1] *) Salt stock solution composition:

[0047]

[Table 2] The TN (total nitrogen) concentration in the outflow water is measured according to JIS K0102.
The nitrogen removal rate was determined by the method described above, and the nitrate ion concentration was measured by ion chromatography. FIG. 3 shows the time-dependent change in the nitrate ion concentration (mg / l) in the outflow water. Furthermore, TN in the effluent water 28 days after the start of the experiment
Table 3 shows the values and the nitrogen removal rate.

Comparative Example 3 Nitrification and denitrification were carried out in the same manner as in Example 2 except that the control carrier prepared in Comparative Example 1 was used instead of the pot-shaped carrier. The obtained results are shown in FIG. 3 and Table 3.

Comparative Example 4 Nitrification and denitrification were carried out in the same manner as in Example 2 except that the PVA carrier prepared in Comparative Example 2 was used instead of the pot-shaped carrier. The obtained results are shown in FIG. 3 and Table 3.

[0050]

[Table 3] As is clear from the results shown in FIG. 3, when the PVA carrier was added, the increase in nitrate ion concentration was significantly slower than when the pot-shaped carrier and the control carrier were added. On the other hand, Table 3
As is clear from the above, when the pot-shaped carrier was added, the TN concentration was lower and the nitrogen removal rate was higher than when the control carrier and the PVA carrier were added. It can be seen that both the nitrification reaction and the denitrification reaction proceeded effectively.

[0051]

As described above, according to the hollow spherical carrier of the present invention, by having a cavity communicating with the outside in the inside thereof, the diameter of the carrier can be increased while suppressing the specific gravity, and good separability can be achieved. And fluidity can be obtained. Furthermore, it is possible to allow air bubbles to be present inside the cavity, and further improve the fluidity, which is particularly suitable as an adherent type carrier for immobilizing microorganisms.

The cavities in the carrier have a structure suitable for increasing the amount of microorganisms retained and for forming an anaerobic condition in the microbial membrane attached to the cavities. It is particularly suitable when both of the reactions are carried out effectively in parallel.

Further, when it is composed of a gelled product obtained by reacting boric acid with cement or a cementitious mineral material, silicon, or polyvinyl alcohol, it is more preferable due to the presence of silanol groups generated by the reaction between silicon and an alkaline component. It is possible to obtain a hollow spherical carrier which has excellent adhesion to microorganisms and which has a porous outer shell part and is excellent in water permeability between the inside and outside of the cavity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of an example of a hollow spherical carrier (vase-shaped carrier) of the present invention.

FIG. 2 is a diagram schematically showing the structure of the reactor used in Example 2.

FIG. 3 is a diagram showing daily changes in nitrate ion concentration in the effluent from the reaction tank in Example 2, Comparative Example 3 and Comparative Example 4.

[Explanation of symbols]

 1 Outer shell 2 Communication hole 3 Cavity 4 Reactor body 5 Silicon stopper 6 Strainer 7 Air diffuser

Claims (11)

[Claims] 1. A hollow spherical body having an outer shell portion forming a cavity therein, wherein the cavity and the outside of the hollow spherical body communicate with each other through a communication hole provided in the outer shell portion. Characterized carrier. 2. The carrier according to claim 1, wherein the diameter of the communication hole is about 1/20 to 1/3 of the diameter of the carrier. 3. The carrier according to claim 1, which has one or two communication holes or a plurality of communication holes in a part of the carrier. 4. The gel material obtained by allowing boric acid to act on a raw material mixture containing cement or a cementitious mineral material containing calcium silicate as a main component, silicon and polyvinyl alcohol, in the outer shell portion. 4. The carrier according to any one of 3 to 3. 5. The carrier according to claim 1, wherein the outer shell is a porous body having water permeability. 6. The carrier according to any one of claims 1 to 5, which is an adherent microbial carrier used by adhering a microorganism thereto. 7. A carrier comprising a hollow spherical body having an outer shell portion forming a cavity therein, wherein the cavity and the outside of the hollow spherical body communicate with each other through a communication hole provided in the outer shell portion. A manufacturing method, comprising: (a) a raw material mixture containing cement or cementitious mineral material containing calcium silicate as a main component, silicon, polyvinyl alcohol and water;
The step of forming a spherical structure by dropping into the boric acid aqueous solution, and (b) the step of permeating the boric acid aqueous solution to a position corresponding to the outer shell of the carrier, the spherical structure from the boric acid aqueous solution. A step of taking out, (c) a step of bringing the spherical structure taken out from the boric acid aqueous solution into contact with water to form the hollow portion and the communication hole, and (d) a hollow spherical structure having the hollow formed therein. After drying, it is placed in a moist environment to obtain the carrier, and a method for producing the carrier. 8. The raw material mixture has the following composition: 10 to 20% by weight aqueous polyvinyl alcohol solution: 50% by weight Cement or cementitious mineral material: 8 to 15% by weight Silicon: 1 to 15% by weight Water: 20 to The method for producing a spherical carrier according to claim 7, containing 41% by weight. 9. The method for producing a spherical carrier according to claim 7, wherein the boric acid aqueous solution is a saturated boric acid aqueous solution. 10. The method for producing a spherical carrier according to claim 7, wherein the spherical structure is aerated and stirred in water in the step (b). 11. A carrier according to any one of claims 1 to 6 in which a microorganism that performs a nitrification reaction under aerobic conditions and an anaerobic microorganism that performs a denitrification reaction under anaerobic conditions are retained.
A biological treatment method for a nitrogen-containing compound, which comprises contacting with a nitrogen-containing compound for nitrification and denitrification.