JPH11207380A - Microorganism carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a microorganism carrier good in adhering of microorganisms to it and large in holding amount of the microorganisms and capable of stably holding a large amount of microorganisms, by using a microorganism carrier for denitrifying bacteria provided with a water absorption gel and inorg. particles adhered to the water absorption gel and specifying the particle size of the inorg. particles. SOLUTION: The microorganism carrier for denitrifying bacteria as the microorganism carrier is composed of the water absorption gel and the inorg. particles adhered to the water absorption gel. The water absorption gel made of a thermoplastic urethane obtained by reacting a long-chain polyol compd. and a short-chain polyol compd. with an isocyanate compd. is used as the water absorption gel. A zeolite having 5-40 μm particle size is used as the inorg. particles. When the particle size is less than 5 μm, an improved effect of the adherability of the microorganism having the particle size of several μm or less than that is not attained since the particle size is too small. And, when the particle size is more than 40 μm, the fluidity of the gel particle is damaged and the adhered amount of the inorg. particles of the water absorption gel is limited since a formed projecting and recessing parts are too large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a microorganism carrier,
In particular, the present invention relates to a microorganism carrier for denitrifying bacteria having excellent adhesion and retention of microorganisms.

[0002]

2. Description of the Related Art In a conventional biological nitrogen removal method, a method of performing a nitrogen removal reaction by floating microorganisms in a biological reaction tank and separating the microorganisms and treated water in a sedimentation tank is generally used.

On the other hand, in recent years, a method of fixing microorganisms on a floating carrier to hold the microorganisms in a reaction tank has been adopted in the field of aerobic treatment, particularly nitrification treatment. Various carriers such as plastic molded products, sponges, gel carriers and the like have been developed as carriers for immobilizing microorganisms by this method.

In the case of using a gel-like carrier, a method of entrapping and immobilizing microorganisms in a gel has been generally used. However, in recent years, instead of entrapping and immobilizing microorganisms, a microorganism film is naturally attached to the carrier. Coupling and fixing methods have begun to be adopted.

[0005] That is, in the entrapping and immobilizing method, since microorganisms are entrapped in the gel carrier in advance, there is an advantage that the reactor is quickly started at the start of the initial operation, but the physical strength is inferior and the reactor is used in the reaction tank. Therefore, there is a drawback that there is a risk of wear or collapse, and that the operation for comprehensive fixation is complicated.

Conventionally, as a gel carrier of the binding and fixing method,
A water-swellable polyurethane gel having continuous pores obtained by reacting a polyol compound, an isocyanate compound and water has been proposed (JP-A-9-51794).

[0007] The gel-like carrier has the following advantages. Polyurethane itself is extremely hydrophilic, has a property of storing a large amount of water therein, and has excellent affinity for microorganisms. Because it has a continuous pore structure even though it is a hydrogel, the microorganisms easily enter the pores of the carrier, and the microorganisms present in the culture solution or the water to be treated efficiently adhere to the outer surface or the pore surface of the carrier, The connection is fixed. There are pores communicating from the carrier surface to the inside,
Even when the surface area of the carrier is large, a large amount of microorganisms in the culture solution or the water to be treated adhere to and are fixed to the carrier, and the microorganisms fixed in the pores are less likely to peel off when flowing. Unlike conventional hydrogels, they have high shear resistance, so that efficient stirring with a propeller or the like is possible in a state where microorganisms are immobilized on the outer surface and inner surface of the pores in a large amount and at a high density.

[0008]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 9-517 is disclosed.
In the case of the gel carrier described in No. 94, good microbial adherence can be obtained.However, in the case of the immobilized microbial carrier, from the viewpoint of starting up the apparatus at the start of operation and improving the operation load, Further improvement of the adhesion of microorganisms is desired.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a microorganism carrier for denitrifying bacteria having extremely good adhesion of microorganisms.

[0010]

Means for Solving the Problems The microorganism carrier of the present invention comprises:
A microorganism carrier for denitrifying bacteria comprising a water-absorbing gel and inorganic particles attached to the water-absorbing gel, wherein the inorganic particles have a particle size of 5 to 40 μm.

In the present invention, although the details of the action mechanism of the effect of improving the adhesion of microorganisms by the inorganic particles attached to the water-absorbing gel are not clear, the inorganic particles having a predetermined particle size increase the unevenness of the gel surface and reduce the roughness. This is presumed to be due to the effect of increasing the surface area, the effect of forming a site that is easily electrochemically attached to the surface of the water-absorbing gel, and the effect of increasing the specific surface area.

In the present invention, zeolite is preferably used as the inorganic particles, and the amount of the zeolite is preferably 3 to 10% by weight based on the weight of the water-absorbing gel when completely dried. In addition, the water-absorbing gel is a water-absorbing gel made of a thermoplastic polyurethane obtained by reacting a long-chain polyol compound and a short-chain polyol compound with an isocyanate compound (hereinafter sometimes referred to as “thermoplastic polyurethane gel”). .).

[0013]

Embodiments of the present invention will be described below in detail.

First, the water-absorbing gel according to the present invention will be described.

As the water-absorbing gel according to the present invention, a thermoplastic polyurethane obtained by reacting a long-chain polyol compound and a short-chain polyol compound with an isocyanate compound, particularly a bifunctional long-chain diol compound, A polyurethane copolymer obtained by reacting a chain diol compound and a bifunctional diisocyanate compound, in which a soft segment and a hard segment are randomly bonded head to tail by a urethane bond, is preferable.

Here, the soft segment obtained by the reaction between the long-chain diol compound and the diisocyanate compound is:
It is represented by the following general formula.

[0017]

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The hard segment obtained by the reaction between the short-chain diol and the diisocyanate compound is represented by the following general formula.

[0019]

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In the above general formula, X represents a portion of the group formed by the reaction of the terminal hydroxyl group of the long-chain diol compound with the isocyanate compound, excluding the terminal hydroxyl group portion. The molecular weight of X is considered to have a great effect on the degree of swelling of the obtained thermoplastic polyurethane gel, and the molecular weight is 1000 to 1300.
0, particularly preferably 4000 to 8000. As the molecular weight of X decreases, the molecular weight of the soft segment decreases,
As a result, the degree of swelling of the obtained thermoplastic polyurethane gel tends to decrease, and the specific gravity of the gel increases. On the other hand, if the molecular weight of X is more than 13,000, problems such as an increase in viscosity and an increase in melting temperature during synthesis are not preferred.

The long-chain diol compound used in the present invention is preferably a water-soluble ethylene oxide / propylene oxide copolymerized polyether-based diol having two terminal hydroxyl groups in one molecule or polyethylene glycol. Here, the content of ethylene oxide is preferably at least 70% by weight, more preferably at least 85% by weight. When the content of ethylene oxide is less than 70% by weight, the degree of swelling of the obtained thermoplastic polyurethane gel may be low.

In the above general formula, Y is
Diisocyanate compound, preferably having a molecular weight of 100 to
It represents a portion of the group formed by the reaction of 1000 diisocyanate compounds with a hydroxyl group, from which the isocyanate group portion has been removed.

Examples of the diisocyanate compound used in the present invention include tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenylmethane diisocyanate, biphenylene diisocyanate, diphenyl ether diisocyanate, tolidine diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

In the above general formula, Z is a short-chain diol compound, preferably a low molecular weight diol compound having a molecular weight of 30 to 400, which is obtained by reacting a terminal hydroxyl group with a diisocyanate compound, excluding the terminal hydroxyl group. It represents.

The short-chain diol compound used in the present invention includes ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 2,3-butanediol, 1,4 -Butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, 1,4-bis -(Β-hydroxyethoxy) benzene, p-xylylenediol, phenyldiethanolamine, methyldiethanolamine, 3,9-bis- (2-hydroxy-
(1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro [5,5] -undecane.

The composition ratio of the long-chain diol compound to the short-chain diol compound in the reaction can be changed depending on the molecular weight of each compound and the desired physical properties of the obtained thermoplastic polyurethane gel. Although it depends on the molecular weight of the long-chain diol compound, the molar ratio of the long-chain diol compound to the short-chain diol compound is preferably in the range of 5: 1 to 1: 2. When the molecular weight of the long-chain diol compound is large, the viscosity tends to increase at the time of synthesis. Therefore, it is preferable to reduce the molar ratio of the short-chain diol compound forming the hard segment. When the volume swelling ratio is increased while maintaining high physical strength, it is preferable to increase the molar ratio of the short-chain diol compound. Further, the number of isocyanate groups of the diisocyanate compound (NCO / O
H) is preferably in the range of 0.95 to 1.8, particularly 1.
More preferably, it is 0 to 1.6.

In the present invention, not only a polyurethane copolymer in which a polymer synthesis reaction has been sufficiently completed, but also an incomplete thermoplastic polyurethane, that is, a polyurethane copolymer in which an active group such as an isocyanate group partially remains is molded. It can also be used after cross-linking.

The method for synthesizing the thermoplastic polyurethane gel used in the present invention includes a prepolymer method in which a long-chain diol compound and a diisocyanate compound are reacted in advance, and then a short-chain diol compound is reacted as a chain extender. Any one-shot method in which the raw materials are all mixed at once can be employed.

The thermoplastic polyurethane gel according to the present invention is plasticized by heating to a melting temperature and exhibits fluidity. Therefore, by extruding a strand (string) or a tube from an extruder having a heating mechanism, and continuously cutting the extruder into an appropriate length, it can be formed into a chip. The shape of the tip can be a cylinder, a cylinder, a prism, a prism, a cube, a disk, a ring, and the like.

The thermoplastic polyurethane gel according to the present invention is extremely advantageous because it can be plasticized by heating and can be formed into an arbitrary shape, and a carrier having a uniform shape and size can be easily and efficiently produced. is there.

This thermoplastic polyurethane gel does not contain water at the time of molding, and swells by absorbing water in the reaction tank when it is put into the reaction tank at the time of use.

In the present invention, the thermoplastic polyurethane gel preferably has a volume swelling ratio with respect to water defined by the following formula (1) in the range of 150 to 4000%.

[0033]

(Equation 1)

In order to determine the volume swelling degree, the thermoplastic polyurethane gel is dried at 100 ° C., and the point at which the weight loss is eliminated is regarded as absolute drying. Further, the sample was immersed in pure water at 25 ° C., and the point at which the volume change disappeared was defined as the time of complete swelling. The volume is determined by measuring the length of each side of a rectangular parallelepiped, cubic or cylindrical sample.

If the degree of volume swelling is less than 150%, the water absorption is too low and the adhesion of microorganisms is poor, and the water content is too low to be called a hydrogel. On the other hand, if the volume swelling degree is more than 4000%, the strength is too low due to water absorption, so that it is not practical.

On the other hand, examples of the inorganic particles having a particle size of 5 to 40 μm according to the present invention include zeolite, anthracite, activated carbon, carbon and the like, and zeolite is particularly preferable.

In the present invention, the particle size of the inorganic particles is 5 μm
If it is less than 10 μm, the effect of improving the adhesion of microorganisms having a size of several μm or less cannot be obtained. In addition, when the particle diameter of the inorganic particles exceeds 40 μm, the formed irregularities are too large, and the fluidity of the gel particles may be impaired, and the amount of the inorganic particles attached to the water-absorbing gel is limited,
The effect of increasing the specific surface area is not desirable because it is smaller than that having a small particle size. In the present invention, the particle diameter refers to a 50% particle diameter of a cumulative curve, that is, a median diameter.

In particular, when zeolite is used as the inorganic particles, it is expected that the adhesion of microorganisms will be good and that the adsorption capacity of zeolite will be effective in absorbing load fluctuations and adsorbing toxic substances. It is.

In order to mix the inorganic particles with the water-absorbing gel and attach the inorganic particles to the surface and / or the inside of the water-absorbing gel, the inorganic particles are added when the water-absorbing gel is in a molten state or extruded from an extruder. After attaching the inorganic powder to the surface of the strand (string) shaped water-absorbing gel,
A method such as cutting can be adopted.

The amount of the inorganic particles attached to the water-absorbing gel is preferably 3 to 10% by weight based on the weight of the water-absorbing gel when absolutely dried. If this ratio is less than 3% by weight, the effect of improving the adhesion of microorganisms by using inorganic particles is not sufficient,
It is technically difficult to attach a large amount of inorganic particles exceeding 10% by weight to the water-absorbing gel.

Although the shape and size of the microorganism carrier of the present invention are not particularly limited, it is usually formed into a columnar shape having a diameter of 2 to 6 mm and a length of 2 to 4 mm in a state of being swollen by absorbing water. It is molded to become.

The microorganism carrier of the present invention is effective as a microorganism carrier for denitrifying bacteria in various biological treatment devices such as a nitrogen removal device and a biofilm filtration device.

The microorganism carrier of the present invention can be effectively used as a gel carrier of a binding and fixing system, but can also be applied to an inclusive fixing system.

[0044]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1, Comparative Examples 1 and 2 (Production of Microorganism Carrier) Polyethylene glycol having an average molecular weight of 6000 was used as a water-soluble polyalkylene ether polyol, and 100 parts by weight of this was charged into a reactor equipped with a stirrer. After preheating at 110 ° C. for 1 hour in a nitrogen gas atmosphere to release water in the polyethylene glycol, the temperature in the reaction vessel was set to 130 ° C. Using 4,4'-diphenylmethane diisocyanate as a polyisocyanate compound, 8.3 parts by weight of this was added to a reaction vessel, and stirred for 2 hours to carry out a prepolymer reaction. Next, 1,4-butanediol was used as a chain extender, and after completion of the prepolymer reaction, 0.4 part by weight of this was added.
Stir for 1 hour. In addition, a series of reactions after preheating,
Performed at 130 ° C. After the completion of the reaction, the contents of the reaction vessel were cast on a vat subjected to a mold release treatment, and heat-treated at 100 ° C. for 4 hours to obtain a thermoplastic polyurethane resin composition.

The thermoplastic polyurethane resin composition thus produced is cooled and finely pulverized, supplied to a multi-screw kneading extruder, and heated and melted at 180 to 230 ° C. while applying a shearing force. It was extruded from an extruder nozzle into a hollow tube having an outer diameter of 1.5 mm. In the cooling step of the extruded tubular strand, the strand is passed through the inorganic particle layer while it is in a molten state, so that the inorganic particles adhere to the surface of the strand and, after further cooling, are cut into a length of 4 mm. As a result, a cylindrical microorganism carrier was produced. Note that zeolite powder having a particle size of 9 μm was used as the inorganic particles, and the attached amount was 5% by weight based on the absolute dry weight of the thermoplastic polyurethane gel. The volume swelling ratio of the thermoplastic polyurethane gel before the attachment of the inorganic particles was 1600%. Further, the specific gravity of the microorganism carrier, that is, the thermoplastic polyurethane gel after the inorganic particles are attached is 1.0.
2 (Example 1).

For comparison, a conventional microbial carrier comprising only a thermoplastic polyurethane gel was produced in the same manner as in Example 1 except that no inorganic particles were used (Comparative Example 1).

A microbial carrier was produced in the same manner as in Example 1 except that zeolite powder having a particle size of 45 μm was used as the inorganic particles (Comparative Example 2).

(Evaluation of Microbial Adhesion) The microbial carriers of Example 1 and the microbial carriers of Comparative Examples 1 and 2 were subjected to an adhesion test of denitrifying bacteria, and the amount of attached microorganisms was examined.
It was shown to.

[0050]

[Table 1]

From Table 1, it can be seen that the microbial carrier of the present invention has markedly improved adhesion of microorganisms and can carry a large amount of microorganisms by having inorganic particles of a predetermined particle size adhere thereto.

(Evaluation of denitrification performance) The microorganism carrier of Example 1 and the microorganism carriers of Comparative Examples 1 and 2 were each placed in a reaction tank in an amount of 50%.
% By volume, and after inoculating seed sludge so that the sludge concentration in the reaction tank would be 200 mg / L, the flow of raw water was started.
The denitrification performance was evaluated. NO ₃ -N concentration of raw water is 25
0 mg / L, and the reaction tank residence time was 50 minutes.

As a result, the attained load one week after the start of water passage was 0.1 mm in the reaction tank filled with the microorganism carrier of Comparative Example 1.
9 kg / m ³ · day, 2.3 kg / m ³ · day in the reaction tank filled with the microbial carrier of Comparative Example 2, whereas 5.1 kg / m ³ · day in the reaction tank filled with the microbial carrier of Example 1. m
^{In 3} days, the performance was 5.6 times that of Comparative Example 1 and 2.2 times that of Comparative Example 2.

[0054]

As described above in detail, the microorganism carrier for denitrifying bacteria comprising the water-absorbing gel and the inorganic particles of the present invention has good adhesion of microorganisms, has a large holding amount, and stably supports a large amount of microorganisms. be able to.

Therefore, the biological treatment apparatus using the microorganism carrier of the present invention can shorten the start-up period of the apparatus at the start of operation, and can stabilize the treatment and increase the tank load. In addition, the processing efficiency can be improved and the size of the apparatus can be reduced.

Claims (4)

[Claims] 1. A microorganism carrier for denitrifying bacteria, comprising a water-absorbing gel and inorganic particles attached to the water-absorbing gel, wherein the inorganic particles have a particle size of 5 to 40 μm. Carrier. 2. The microorganism carrier according to claim 1, wherein the inorganic particles are zeolites. 3. The microorganism carrier according to claim 1, wherein the amount of the inorganic particles attached is 3 to 10% by weight based on the weight of the water-absorbing gel when completely dried. 4. The water-absorbing gel according to claim 1, wherein the water-absorbing gel is made of a thermoplastic polyurethane obtained by reacting a long-chain polyol compound and a short-chain polyol compound with an isocyanate compound. A microorganism carrier, which is a gel.