JP7703203B2 - Microorganism carrier and method for producing same - Google Patents

Description

The present invention relates to a microbial carrier (hereinafter simply referred to as a carrier) and a method for producing the same, and in particular to a microbial carrier that supports, grows, and detaches microorganisms, and a method for producing the same.

Methods using microorganisms are known for purifying industrial wastewater such as factory effluent, domestic wastewater, water for raising fish and shellfish, water for raising aquatic plants, etc. For example, by introducing a carrier carrying microorganisms into the water to be treated and allowing the water to pass through, the microorganisms can act to decompose harmful substances in the water. Such microorganisms include aerobic microorganisms that require oxygen to grow, and anaerobic microorganisms that do not require oxygen to grow.

Carriers made of ceramic powder, which is an inorganic powder, have been known as carriers. Ceramics have many pores on their surface, making them suitable for the attachment of microorganisms. For example, Patent Document 1 describes a carrier made of a ceramic molded body containing wollastonite and anorthite. Two types of pores are formed on the surface of this carrier, with large pores having diameters in the range of 50 to 1000 μm and fine pores having diameters in the range of 0.1 to 10 μm.

There is also a known technology that uses waste foundry sand generated during the casting manufacturing process as a microbial carrier. For example, Patent Document 2 describes a carrier made by heat-treating waste foundry sand at 180°C or higher and 400°C or lower.

Japanese Patent Application Publication No. 7-60279 JP 2018-114494 A

Carriers made of ceramic molded bodies have a large surface area due to their porous structure, and are excellent for attaching microorganisms. However, the carriers are heavy and difficult to handle. In addition, they require firing, which tends to increase costs. The same can be said for carriers made from waste foundry sand. On the other hand, carriers made of resin molded bodies are also known as lightweight, relatively low-cost carriers, but they tend to have a smaller surface area and are inferior in terms of durability compared to carriers made of ceramic molded bodies.

In order to fully utilize the activity of the microorganisms supported on the carrier, it is important to bring as much of the water to be treated into contact with the microorganisms as possible. For this reason, the treatment capacity is generally improved by stirring the water to be treated and the carriers to keep them moving, but it would be desirable to be able to improve the treatment capacity of the microorganisms in a simpler way.

The present invention was made to address these circumstances, and aims to provide a microbial carrier that is easy to handle and has excellent microbial processing capabilities, as well as a method for producing the same.

The microbial carrier of the present invention is a microbial carrier that supports microorganisms, and the microbial carrier is a foamed molded product containing a thermoplastic resin and an inorganic powder, has an uneven surface, and is characterized in that the inorganic powder is contained in an amount of 15% by mass to 70% by mass based on the total amount of the thermoplastic resin and the inorganic powder. The foamed molded product is an extruded foamed molded product, and the inorganic powder is contained in an amount of 35% by mass to 70% by mass based on the total amount of the thermoplastic resin and the inorganic powder.

The inorganic powder is characterized in that it is at least one selected from the group consisting of silicon dioxide, aluminum oxide, calcium silicate hydrate, diatomaceous earth, bakuhan stone, shells, bone powder, calcium carbonate, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, wollastonite, anorthite, and mica.

The specific surface area of the microorganism carrier is characterized in that it is 1 m ² /g to 5 m ² /g.

The method for producing the microbial carrier of the present invention is characterized by kneading at least the thermoplastic resin, the inorganic powder, and a foaming agent, and foaming molding the mixture.

The manufacturing method is characterized in that the raw materials other than the foaming agent are pelletized in advance, and the pellets are mixed with the foaming agent and extruded for foaming.

The microbial carrier of the present invention is a foamed molded product containing a thermoplastic resin and an inorganic powder, has an uneven surface, and contains 15% to 70% by mass of inorganic powder relative to the total amount of the thermoplastic resin and inorganic powder, so that the amount of microorganisms adhering to the carrier is increased, and the processing capacity of the microorganisms can be improved. In addition, by combining the thermoplastic resin and the inorganic powder, a microbial carrier is obtained that combines the characteristics of a lightweight resin with the inorganic powder that has a large specific surface area and is durable.

Furthermore, the above-mentioned microbial carrier surprisingly has the function of supporting and growing microorganisms, as well as the function of releasing the microorganisms once supported on the carrier into water (detachment function). As shown in the examples described later, the microbial carrier of the present invention has an excellent detachment function. This is thought to be because the combination of thermoplastic resin and inorganic powder creates an appropriate relationship between the potential of the carrier and the potential of the microorganisms. In this way, with the microbial carrier of the present invention, it becomes possible to treat the water to be treated even with the microorganisms detached from the carrier, and the treatment capacity of the microorganisms can be easily improved.

The method for producing a microbial carrier of the present invention involves kneading at least a thermoplastic resin, an inorganic powder, and a foaming agent to form a foam, so there is no need for firing as with carriers made of ceramic molded bodies, and the carrier can be produced relatively inexpensively.

In the above manufacturing method, the raw materials other than the foaming agent are pelletized in advance, and the pellets are mixed with the foaming agent to perform extrusion foaming. Therefore, even if the content of inorganic powder is increased, it is easy to ensure the dispersibility of the inorganic powder in the carrier. In addition, it becomes easier to disperse the foaming agent throughout the composition, making it easier to prevent uneven distribution of pores.

FIG. 1 is a diagram showing an example of a microorganism carrier of the present invention. FIG. 1 is a diagram showing an example of a method for producing a microorganism carrier of the present invention. FIG. 1 is a schematic diagram showing the use of the microbial carrier of the present invention for probiotics on fish skin. FIG. 1 is a schematic diagram showing the use of the microbial carrier of the present invention in a biological deodorization system. 1 is a photograph showing the appearance of the carriers of Examples 1 to 3. 1 is a micrograph and an SEM photograph of a cross section of the support of Example 1. 4 is a micrograph and an SEM photograph of a cross section of the support of Example 2. 4 is a micrograph and an SEM photograph of a cross section of the support of Example 3. FIG. 1 shows the results of a growth inhibition test of KH-ZF1 against pathogenic microorganisms. FIG. 1 shows the properties of carriers used in microbial growth and detachment tests. FIG. 1 is a schematic diagram of a microbial growth and detachment test. 1 is a photograph showing the results of a microbial growth and detachment test.

An example of the microbial carrier of the present invention will be described with reference to FIG. 1. FIG. 1(a) shows a perspective view of the carrier, and FIG. 1(b) shows a schematic cross-sectional view of a portion of the carrier. This carrier supports microorganisms, and is used, for example, underwater, where the microorganisms act to decompose, inactivate, remove, inhibit growth, kill, etc., specific substances in the water to be treated. Specific substances include substances that have adverse effects on the human body, seafood, etc. (for example, harmful substances such as ammonia and pathogenic microorganisms), unwanted materials, etc.

As shown in FIG. 1(a), the carrier 1 is an extrusion foam molded product containing a thermoplastic resin and an inorganic powder, and has a large number of irregularities 2 on its surface. The irregularities 2 are irregularities formed on the surface of the molded product when the carrier is extrusion foam molded, and are also called melt fractures. Specifically, the irregularities 2 are formed by partial elevation of the resin portion due to foaming, and are rougher than the fine irregularities (on the order of several microns) formed by general roughening treatments such as etching. The irregularities 2 are formed over almost the entire cylindrical outer surface 1a and cylindrical inner surface 1b. Although FIG. 1 shows an extrusion foam molded product, an injection foam molded product may also be used as the foam molded product. In this case, the irregularities on the surface are formed by the foamed resin portion and the inorganic powder exposed on the surface.

The size of the carrier 1 is not particularly limited, but for example, the outer diameter φ is 10 mm to 50 mm, and the axial length L is 20 mm to 100 mm. The axial length L of the carrier 1 is in the same direction as the direction of extrusion from the extruder, and is adjusted according to the cut length of the molded body extruded from the extruder. The shape of the carrier 1 is not limited to a cylinder, and may be a columnar body, sphere, cube, rectangular parallelepiped, etc.

As shown in FIG. 1(b), in the carrier 1, inorganic powder 4 is dispersed in thermoplastic resin 3. In the carrier 1, communicating holes 6 and closed holes 7 are formed as pores 5 generated by foam molding. The communicating holes 6 are holes that communicate with the cylindrical surfaces 1a and 1b, and the closed holes 7 are holes that are surrounded by wall surfaces. As shown in FIG. 1(b), a portion of the inorganic powder 4 is exposed inside the pores 5 and on the cylindrical surfaces 1a and 1b, and is configured to come into contact with the water to be treated.

As shown in Fig. 1(b), the carrier 1 has a porous structure, and the specific surface area is preferably 0.1 ^m2 /g or more from the viewpoint of adhesion of microorganisms. As a specific range, the specific surface area is preferably 0.1 ^m2 /g to 10 ^m2 /g, and more preferably 1 ^m2 /g to 5 ^m2 /g. The specific surface area refers to a value measured by a nitrogen gas adsorption method. The nitrogen gas adsorption method is performed by measuring the amount of adsorbed and desorbed nitrogen gas per unit mass.

The bulk density of the carrier 1 is preferably 0.9 g/cm ³ to 2 g/cm ^3. The bulk density is measured using an apparent density measuring device conforming to JIS K6911. By setting the bulk density within the above range, the carrier can be easily made to flow in water, and the treatment capacity by the microorganisms can be improved. The bulk density is more preferably 0.9 g/cm ³ to 1.5 g/cm ³ , and even more preferably 0.9 g/cm ³ to 1.2 g/cm ³ .

The composition of the microbial carrier of the present invention is described below.

The thermoplastic resin is not particularly limited, and examples thereof include polyolefin resins such as polyethylene (PE) resin and polypropylene (PP) resin, polystyrene resins, ABS (acrylonitrile butadiene styrene) resin, vinyl chloride resin, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, and polycarbonate resins. These may be used alone or in combination of two or more types. Among the above thermoplastic resins, polyolefin resins are preferred because of their light weight and excellent moldability.

The thermoplastic resin is preferably contained in an amount of 30% to 85% by mass, and more preferably 30% to 65% by mass, based on the total amount of the thermoplastic resin and the inorganic powder. If the content is less than 30% by mass, it may be difficult to ensure flowability during molding, and the retention of the inorganic powder may be reduced. The content of the thermoplastic resin may be less than that of the inorganic powder in terms of mass ratio.

In the microbial carrier, the inorganic powder is contained in an amount of 15% by mass to 70% by mass, preferably 35% by mass to 70% by mass, based on the total amount of the thermoplastic resin and the inorganic powder. The inorganic powder is not particularly limited, and natural products such as minerals, fine ceramics, shells, bone powder, etc. can be used. Examples of minerals include diatomaceous earth, bakuhan stone, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, wollastonite, anorthite, mica, etc. Note that these minerals may be natural minerals or artificially synthesized ones (e.g., synthetic zeolite). Examples of fine ceramics include aluminum nitride, silicon carbide, silicon nitride, boron nitride, alumina, etc. Examples of shells include oyster and pearl oyster shells. In addition, silicon dioxide, which is a component contained in minerals and shells, aluminum oxide, calcium silicate hydrate, calcium carbonate, etc. can also be used as inorganic powder. The inorganic powders may be used alone or in combination of two or more types.

The average particle size of the inorganic powder is not particularly limited, but is preferably 1 μm to 100 μm. If the average particle size of the inorganic powder exceeds 100 μm, dispersibility in the resin may decrease, and the amount of inorganic powder exposed to the carrier surface or pores of the carrier may decrease. On the other hand, if the average particle size of the inorganic powder is less than 1 μm, aggregation between particles may occur easily, which may impair dispersibility. The average particle size is obtained by measurement using a laser diffraction/scattering method.

The inorganic powder is preferably at least one selected from the group consisting of silicon dioxide, aluminum oxide, calcium silicate hydrate, diatomaceous earth, Maifan stone, shells, bone meal, calcium carbonate, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, wollastonite, anorthite, and mica, and more preferably at least one of diatomaceous earth and zeolite. Diatomaceous earth is made up of fossils of diatoms, a type of algae, and is a porous rock whose main component is silicon dioxide. Diatomaceous earth contains small amounts of alumina, iron oxide, and other components. In addition, by using diatomaceous earth, which has excellent water absorption and hygroscopic properties, as the inorganic powder, water absorption can be imparted to the carrier.

Zeolite is called a crystalline aluminosilicate and contains silicon, aluminum, and oxygen atoms. Many zeolite framework structures are known, and LTA-type zeolite, FER-type zeolite, MWW-type zeolite, MFI-type zeolite, MOR-type zeolite, LTL-type zeolite, FAU-type zeolite, etc. can be used. Zeolite is also known to adsorb harmful ammonia from fish droppings and food residues and release sodium, making it suitable for use in fish breeding water, for example.

In a configuration that includes diatomaceous earth as an inorganic powder, the diatomaceous earth is contained in an amount of, for example, 15% by mass to 55% by mass, and preferably 20% by mass to 45% by mass, based on the total amount of the thermoplastic resin and the inorganic powder. In a configuration that includes zeolite as an inorganic powder, the zeolite is contained in an amount of, for example, 15% by mass to 55% by mass, and preferably 20% by mass to 45% by mass, based on the total amount of the thermoplastic resin and the inorganic powder. In a configuration that includes diatomaceous earth and zeolite, the above numerical ranges can also be used. Furthermore, in this case, it is preferable that the content of diatomaceous earth is greater than the content of zeolite.

The carrier of the present invention is a foamed molded body, which is obtained by foam molding using a foaming agent. This carrier may contain a component derived from the foaming agent. As the foaming agent, a physical foaming agent or a chemical foaming agent is used. Examples of physical foaming agents include hydrocarbons such as propane, butane, and pentane, chlorinated hydrocarbons such as dichloroethane and dichloromethane, fluorinated chlorinated hydrocarbons such as trichloromonofluoromethane and dichlorodifluoromethane, carbon dioxide gas, nitrogen gas, and water. Examples of chemical foaming agents include azo compounds such as sodium bicarbonate and barium azodicarboxylate, and nitroso compounds such as N,N-dinitrosopentamethylenetetramine.

The carrier may be blended with a lubricant to improve fluidity during molding. Examples of lubricants include aliphatic hydrocarbons such as synthetic paraffin, higher fatty acids such as stearic acid, higher aliphatic alcohols, metal soaps such as sodium stearate, and higher fatty acid esters. The amount of lubricant blended is, for example, 0.5% to 10% by mass based on the total amount of the thermoplastic resin and inorganic powder. In addition, other well-known additives may be blended with the microbial carrier of the present invention.

The water absorption rate of the carrier is preferably 5% or more. If the water absorption rate is 5% or more, the carrier quickly becomes compatible with water, and is therefore easy to fill in a filtration tank when immersed therein. In addition, since the carrier comes into frequent contact with the water to be treated, the proliferated microorganisms are more likely to be released gradually. The water absorption rate of the carrier is more preferably 5% to 15%. The water absorption rate is measured by the method described in the Examples below.
The pH of the solution leached from the carrier is preferably near neutral, more preferably from 6.0 to 8.5, and more preferably from 6.5 to 8.0.

Next, an example of a method for manufacturing the carrier of the present invention will be described with reference to FIG. 2. FIG. 2 shows a manufacturing method using extrusion foam molding, but the carrier may also be manufactured by injection foam molding. In the method shown in FIG. 2, raw materials other than the foaming agent are obtained in advance as pellets 18. The pellets 18 are obtained, for example, by kneading a thermoplastic resin, an inorganic powder, and a lubricant, extruding the kneaded mixture with a pelletizer, and then cutting it to a predetermined length. The lubricant is added as necessary.

As shown in FIG. 2, pellets 18 and foaming agent 19 are introduced into the cylinder 13 by being charged into the hopper 12 of the extrusion molding machine 11. In the cylinder 13, the pellets 18 and foaming agent 19 are heated and melted by the heater 14, kneaded by the screw 15, and transferred from the cylinder nozzle 16 to the die 17. Then, bubbles are formed due to the pressure drop as the molten mixture flows through the die 17, and an extruded foam is obtained.

The amount of foaming agent and the expansion ratio in the foam molding are adjusted as appropriate. The amount of foaming agent is not particularly limited, but is, for example, 1% to 60% by mass, preferably 20% to 60% by mass, and more preferably 40% to 60% by mass, based on the total amount of thermoplastic resin and inorganic powder.

In the method shown in FIG. 2, a chemical foaming agent is used as the foaming agent 19, but a physical foaming agent may be used instead. For example, when the foaming agent is a gas such as carbon dioxide, the gas is added to the molten pellets 18 in a predetermined ratio under pressure control in the cylinder 13 and kneaded.

Also, as shown in FIG. 2, each raw material may be directly fed into the hopper 12 of the extrusion molding machine 11 without obtaining the pellets 18 in advance. In this case, the thermoplastic resin, inorganic powder, lubricant, and foaming agent are fed into the hopper 12, kneaded, and extrusion foam molding is performed as described above. However, the method of pre-kneading and obtaining the pellets 18 in advance is preferable, since it allows a larger amount of inorganic powder to be mixed and allows bubbles to be formed uniformly throughout the carrier.

The carrier of the present invention is used, for example, underwater to improve the quality of the water to be treated. The microorganisms supported on the carrier may be any microorganism capable of decomposing a specific substance in the water to be treated, and may be either aerobic or anaerobic. For example, the genus Pseudomonas, the genus Rhodococcus, the genus Alcaligenes, the genus Burkholderia, the genus Bacillus, the genus Corynebacterium, the genus Acinetobacter, the genus Rhodobacter, the genus Bacillus, the genus Bacillus, the genus Corynebacterium, the genus Acinetobacter, the genus Bacillus ... Microorganisms that can be used include those of the genera Rhodobacter, Ralstonia, Acidovorax, Serratia, Flavobacterium, and nitrifying bacteria (such as those of the genera Nitrosomonas and Nitrobacter). The microorganisms used are appropriately selected depending on the conditions of use of the carrier. For example, when used in water for breeding fish and shellfish, the microorganisms are appropriately selected depending on the type of fish and shellfish and the type of fish disease.

The carrier of the present invention can support (adhere), grow, and detach (slow-release) the above-mentioned microorganisms. Conventionally, the performance of a general carrier (especially in water treatment) was judged by how well the microorganisms were attached and how well they were multiplied, and there was no concept of "slow-release". In a carrier that only has the function of adhering and growing microorganisms, the function is mainly exerted on the contact surface, so how to bring the carrier into contact with the water to be treated is important. In contrast, the carrier of the present invention, which has the three functions of adhering, growing, and slow-release, slowly releases microorganisms, so measures for bringing the carrier into contact with the water to be treated can be reduced. In addition, the microorganisms that have been detached (slow-released) from the carrier can further attach to other carriers in the water to be treated, structures, and the surfaces of living organisms such as fish and shellfish, and can exert microbial activity there. The detached microorganisms may also aggregate to form flocs or granules. In this way, by using the carrier of the present invention, excellent water treatment capabilities can be exerted, and the water quality of various wastewater, fish farms, aquariums, etc. can be efficiently improved.

An example of the use of the carrier of the present invention is its use in aquaculture. In recent years, closed circulation land-based aquaculture has been attracting attention. This type of aquaculture is less susceptible to external factors such as weather and red tides because the environment is controlled within a closed facility, and the water temperature can be adjusted, making it highly productive. However, since it is a closed environment, water quality management is particularly important, and problems such as fish and shellfish becoming ill due to deterioration of water quality are being considered. In particular, since fish are often raised under high density in aquaculture, the skin of the fish is easily damaged due to contact between fish, and these wounds may lead to the development of infectious diseases. For these reasons, it is possible to use probiotics targeted at the skin of fish.

Figure 3 shows a schematic diagram of the use of microorganisms carried on the carrier of the present invention as probiotics for fish skin. First, microorganisms useful as probiotics are added to a carrier, and the carrier is then placed in water in which farmed fish are raised. The microorganisms carried on the carrier grow under normal rearing conditions (e.g., about 20-30°C, pH 6.0-8.5) to form a biofilm. The grown microorganisms then steadily detach from the carrier and settle on the fish's skin. The gradual release of the microorganisms from the carrier allows a continuous supply of microorganisms to the fish. Then, the action of the microorganisms that have settled on the epidermis can prevent infection by pathogenic microorganisms.

The microorganisms used in Figure 3 are preferably aerobic microorganisms, as they are intended to be established on the epidermis of fish to prevent disease. Specifically, microorganisms of the genus Pseudomonas are more preferred, with Pseudomonas mosselii, Pseudomonas marginalis, Pseudomonas koreensis, Pseudomonas protegens, or Pseudomonas parafulva being even more preferred.

Examples of fish and shellfish that can be farmed include eel, sweetfish, yellowtail, trout, sea bream, carp, amberjack, tuna, salmon, horse mackerel, flounder, tilapia, pufferfish, yellowtail, grouper, mackerel, saury, catfish, and shrimp.

Another example of the use of the carrier of the present invention is in a biological deodorization system. FIG. 4 shows a schematic diagram of an example of a biological deodorization system. Biological deodorization systems are mainly used as odor treatment devices in sewage treatment plants and in the treatment of organic waste such as livestock manure. As shown in FIG. 4, the biological deodorization system 21 mainly comprises a biological deodorization tower 22 that uses a microbial carrier 23 to deodorize odorous gases, and an activated carbon adsorption tower 28 that uses activated carbon to adsorb and desorb odorous gases. In FIG. 4, an eliminator 26 and a deodorization fan 27 are installed in the path connecting the biological deodorization tower 22 and the activated carbon adsorption tower 28.

First, the odorous gas introduced from the bottom of the biological deodorization tower 22 passes through the microorganism carrier 23 and is discharged from the exhaust port at the top. A sprinkler pipe 24 is installed at the top of the biological deodorization tower 22, and supply water containing nutrients is sprayed onto the microorganism carrier 23 by the sprinkler pipe 24 to provide a nutrient source to the microorganisms. The water that accumulates at the bottom of the biological deodorization tower 22 is drained after a process such as pH measurement. The odorous gas discharged from the biological deodorization tower 22 is introduced into the activated carbon adsorption tower 28 via the eliminator 26 and deodorization fan 27. Then, it is introduced into the bottom of the activated carbon adsorption tower 28, and as it rises, it is deodorized by passing through the activated carbon filled in the activated carbon filling section 29. The gas discharged from the activated carbon adsorption tower 28 is released into the atmosphere, etc.

Conventionally, in order to adhere deodorizing microorganisms to the microbial carriers used in these biological deodorization systems, it was necessary to pack the carriers (string-like, pumice-like, etc.) densely and run water through them for one to two months to allow them to grow. Furthermore, while the carriers were packed densely to increase the contact area, in reality the microorganisms often did not spread throughout the entire carrier, and they only adhered and multiplied in parts. As a result, the equipment had to be made larger to increase effectiveness, which led to problems such as increased initial costs.

By applying the carrier of the present invention to the microorganism carrier 23 in the biological deodorization tower 22, it is believed that the microorganisms that have grown on the carrier are effectively released, making it possible to significantly shorten the training time. In addition, the sustained release action makes it easier for the microorganisms to spread throughout the entire carrier, which also leads to the miniaturization of the device. Furthermore, even during use, the microorganisms are released by the water sprayed from the spray pipe 24, which is expected to provide an even greater deodorizing effect.

The carrier of the present invention is also believed to be effective in other soil and wastewater treatment processes. Currently, soil treatment involves waiting for the diffusion of useful microorganisms or forcibly stirring the soil, but by using the carrier of the present invention, it is possible to effectively release the microorganisms and improve the treatment capacity of the microorganisms.

Microorganism carriers were produced by each molding method using the raw materials shown below.
Thermoplastic resin: polypropylene resin Inorganic powder: diatomaceous earth and zeolite (mass ratio 3:2)
Lubricant: stearic acid and paraffin Foaming agent: inorganic foaming agent Cellmic 417 (manufactured by Sankyo Kasei Co., Ltd.)

Example 1
The thermoplastic resin was used in an amount of 40.0% by mass, and the inorganic powder was used in an amount of 60.0% by mass, based on the total amount of the thermoplastic resin and the inorganic powder. The foaming agent was used in an amount of 50.0% by mass, based on the total amount of the thermoplastic resin and the inorganic powder. According to the method of FIG. 2, the thermoplastic resin and the inorganic powder were pelletized in advance, and then the pellets and the foaming agent were simultaneously charged into the hopper of the extrusion molding machine, kneaded, and extrusion foam molding was performed. The rod-shaped molded body discharged from the die was cooled in a water bath, and then cut to a length of 10 mm. The appearance photograph of the obtained extruded foam molding is shown in FIG. 5(a). In addition, FIG. 6(a) shows a micrograph of a cross section cut along the radial direction of the extruded foam molding, FIG. 6(b) shows a micrograph of a cross section cut along the axial direction, and FIG. 6(c) and (d) show SEM photographs at various magnifications.

Example 2
The thermoplastic resin was used in an amount of 57.1% by mass, the inorganic powder in an amount of 42.9% by mass, and the lubricant in an amount of 0.9% by mass, based on the total amount of the thermoplastic resin and the inorganic powder. The foaming agent was used in an amount of 1.4% by mass, based on the total amount of the thermoplastic resin and the inorganic powder. The thermoplastic resin, the inorganic powder, the lubricant, and the foaming agent were directly fed into an extrusion molding machine without pre-mixing, and extrusion foam molding was performed. The appearance photograph of the obtained extruded foam molding is shown in FIG. 5(b). Also, FIG. 7 shows a photograph similar to FIG. 6.

Example 3
The thermoplastic resin was used in an amount of 76.7% by mass, the inorganic powder in an amount of 23.3% by mass, and the lubricant in an amount of 3.8% by mass (stearic acid 2.2% by mass, paraffin 1.6% by mass) based on the total amount of the thermoplastic resin and the inorganic powder. The foaming agent was used in an amount of 5.4% by mass based on the total amount of the thermoplastic resin and the inorganic powder. The thermoplastic resin, the inorganic powder, the lubricant, and the foaming agent were directly put into an injection molding machine without pre-mixing, and injection foam molding was performed. A photograph of the appearance of the obtained injection foam molded body is shown in FIG. 5(c). Also, FIG. 8 shows a photograph similar to FIG. 6. In FIG. 6 to FIG. 8, the black parts in the carrier indicate pores, the white parts indicate inorganic powder, and the remaining parts indicate resin.

As shown in Figures 5 to 8, the carriers of Examples 1 to 3 have unevenness on their surfaces due to foam molding. The carriers of extruded foam moldings have a greater degree of unevenness on the cylindrical surface than the carriers of injected foam moldings, and many pores were observed. In particular, the carrier of Example 1 has unevenness over its entire surface, and has a higher shape uniformity than the carrier of Example 2. In addition, the carrier of Example 1 has inorganic powder and pores evenly dispersed throughout the carrier (see Figure 6), whereas the carrier of Example 2 shows a tendency for inorganic powder and pores to be unevenly distributed (see Figure 7).

Next, the physical properties of each of the resulting molded bodies were measured using the methods described below. The results are shown in Table 1.

The water absorption rate was calculated from the following formula (1): In the formula (1), W1 indicates the weight of a 10 mm × 10 mm × 10 mm test piece taken from each molded body, measured after drying at 105°C for one day, and W2 indicates the weight W2 measured after immersing each dried test piece in 50 mL of distilled water for 24 hours and removing the moisture on the surface of the test piece.
Water absorption rate (%) = (W2-W1)/W1×100...(1)

Five test pieces, each measuring approximately 10 mm in length and 10-15 mm in diameter, were taken from each molded body and immersed in 50 mL of distilled water for 30 minutes for preliminary cleaning. After cleaning, excess water was wiped off the test pieces and they were immersed in a container containing 200 mL of distilled water, the lid of the container was closed and the specimens were left to stand at room temperature. The lid was opened periodically (after 1 day, 3 days, and 1 week) and the pH was measured.

The specific surface area was measured by the nitrogen gas adsorption method using a specific surface area meter (manufactured by Nippon Bell Co., Ltd.).

The bulk density was determined from the following formula (2) using an apparent density measuring device in accordance with JIS K6911.
Bulk density=[(weight of measuring cylinder containing sample (g))−(weight of measuring cylinder (g))]/(volume of measuring cylinder (cm ³ )) (2)

As shown in Table 1, the carriers of Examples 1 and 2 had a specific surface area of 1 ^m2 /g or more, which was larger than that of the carrier of Example 3. This result is believed to be largely due to the difference in the surface shape of each carrier. The carriers of Examples 1 and 2 also had a higher water absorption rate than the carrier of Example 3. In Examples 1 and 2, a large amount of inorganic powder was exposed on the cylindrical surface and inside the pores, and this is believed to be the reason for the water absorption effect of this exposed inorganic powder. The pH of the liquid leached from the carriers of Examples 1 and 2 was almost neutral.

Next, microorganisms were added to multiple carriers, and the growth and detachment of the microorganisms in water were observed. The microorganism used in this test was KH-ZF1 (NITE BP-02967). KH-ZF1 is a microorganism isolated from the epidermal mucosa of zebrafish (Danio rerio), and has been identified as Pseudomonas mosselii by molecular phylogenetic analysis using the 16s ribosomal RNA gene sequence.

KH-ZF1 was obtained by the following procedure. The mucous membrane on the surface of the zebrafish body was scraped with a cotton swab, and the swab was immersed in 1 mL of ultrapure water and stirred to obtain a suspension. 200 μL each of this suspension and dilution solution (a solution obtained by diluting the suspension 5 times with ultrapure water) were dropped and spread onto Nutrient Broth agar medium (NB agar medium), Enriched Cytophaga agar medium, and modified Zobell 2216E agar medium. Each agar medium was then cultured at 28°C for 2 days. After the culture, the obtained colonies were screened to obtain KH-ZF1.

9 shows the results of a growth inhibition test of KH-ZF1 against pathogenic microorganisms. In this test, the pathogenic microorganisms used were Aeromonas caviae, Aeromonas hydrophila (ATCC700183), Aeromonas hydrophila (JCM1027), Yersinia ruckeri (NVH3578), Yersinia ruckeri (DSMZ18506), Edwardsiella tarda (NRIA44), Edwardsiella tarda (NRIA51), Vibrio angillarum, Vibrio ordalii, and Streptococcus iniae. Two types of non-pathogenic microorganisms were used as negative controls. A cell suspension of KH-ZF1 (KH-ZF1 was cultured on NB agar medium, centrifuged at 5000×g for 10 minutes, the precipitated cells were collected, and resuspended in sterilized water to an OD ₆₀₀ of 1.0) was prepared. This suspension was impregnated into a paper disk placed in the center of the NB agar medium in a petri dish and allowed to stand at 20°C for two days. Thereafter, the test microorganisms were streaked radially from the addition site of KH-ZF1 without touching KH-ZF1, and cultured at 20°C for two days. As shown in FIG. 9, selective inhibition of pathogenic microorganisms was confirmed compared to non-pathogenic microorganisms.

In the microbial growth and detachment tests, the carriers of Example 4 and Comparative Examples 1 to 4 shown in Figure 10 were used. The carrier of Example 4 was prepared in the same manner as the carrier of Example 1 described above.

The carrier in Comparative Example 1 is a carrier whose main component is waste foundry sand, and BTS (Biotope Sand, manufactured by Ezaki Sangyo Co., Ltd.) black soil was used. The main components of this carrier are silicon dioxide (about 49%), carbon (about 15%), _{and Fe2O3} (about 11%).

The carrier in Comparative Example 2 is a carrier whose main component is waste foundry sand, and was prepared by firing the carrier in Comparative Example 1 at 700-800°C.

The carrier of Comparative Example 3 was made of a ceramic molded body, and was prepared as follows. 60 parts by mass of diatomaceous earth was mixed with 20 parts by mass of gairome clay, which is a kaolin clay and an aluminum-containing clay mineral, and 20 parts by mass of rice bran. An appropriate amount of water was added to this mixture, which was then kneaded and coated and granulated to obtain a spherical molded product. This molded product was fired at 900 to 950°C to obtain the carrier. The main components of this carrier were silicon dioxide (about 78%) and Al ₂ O ₃ (about 15%).

The carrier of Comparative Example 4 was a carrier made of a ceramic molded body, and was prepared as follows. 65 parts by mass of crushed lightweight cellular concrete (ALC) mainly composed of tobermorite, a type of calcium silicate hydrate, was mixed with 30 parts by mass of frog-eye clay and 5 parts by mass of inorganic reinforcing fiber (sepiolite), and 20 parts by mass of a powdery organic void-forming material was further mixed with 100 parts by mass of the resulting mixture to obtain a molding material. An appropriate amount of water was added to this molding material and kneaded, and the resulting kneaded product was fed to an extrusion molding machine to obtain a molding product. The molding product was fired at 1000 to 1100°C to obtain a carrier. The main components of this carrier were silicon dioxide (about 55%), calcium oxide (about 16%), and Al ₂ O ₃ (about 14%).

Each of the carriers obtained above was subjected to the test shown in FIG. 11. First, 20 μL of KH-ZF1 was added to each carrier so that OD ₆₀₀ = 1.5. The carriers to which KH-ZF1 was added were placed in 20 mL of rearing water and incubated at 20° C. for 24 hours. The rearing water was then replaced, and the carriers were incubated at 20° C. for 1 week in the newly added 20 mL of rearing water. The carriers after 24 hours of incubation and the carriers after 1 week of incubation were observed under a microscope. In addition, the rearing water after 1 week of incubation was seeded on a selective medium, Pseudomonas isolation agar medium (manufactured by Becton Dickinson) containing kanamycin, and cultured at 28° C. for 1 day, and the amount of KH-ZF1 was observed by colony formation. These results are shown in FIG. 12.

As shown in Figure 12, KH-ZF1 was supported on all of the carriers in Example 4 and Comparative Examples 1 to 4 after 24 hours. In addition, the supported KH-ZF1 was observed to grow after one week on all of the carriers. Since all of these carriers have a porous structure, they are considered to be excellent in terms of microbial adhesion, that is, in terms of the ability to support and grow microorganisms.

On the other hand, detachment of microorganisms was significantly observed when the carrier of Example 4 was used. As shown in FIG. 12, in Example 4, numerous colonies were observed over almost the entire culture medium on the petri dish. In contrast, no colonies were observed in Comparative Examples 1 to 3, and the number of colonies was small in Comparative Example 4. From these results, it was found that the carrier of Example 4 is excellent in supporting and growing microorganisms, as well as in the ability to detach microorganisms into water. With the carrier of Example 4, microbial activity can be exerted not only on the carrier, but also in places where microorganisms detached from the carrier newly attach, and therefore the water treatment ability of microorganisms can be further improved.

The microbial carrier of the present invention is easy to handle and has excellent microbial processing capabilities, making it useful for purifying industrial wastewater such as factory wastewater, domestic wastewater, fish breeding water, and water for breeding aquatic plants.

1. Carrier (Microorganism Carrier)
2 unevenness 3 thermoplastic resin 4 inorganic powder 5 air hole 6 communicating hole 7 closed hole 11 extrusion molding machine 12 hopper 13 cylinder 14 heater 15 screw 16 cylinder nozzle 17 die 18 pellets 19 foaming agent 21 biological deodorization system 22 biological deodorization tower 23 microorganism carrier 24 sprinkler pipe 25 drain valve 26 eliminator 27 deodorization fan 28 activated carbon adsorption tower

Claims (4)

An underwater microorganism carrier used in water and carrying microorganisms,
The underwater microorganism carrier is an extrusion foam (excluding steam-extrusion foam) containing a thermoplastic resin and an inorganic powder, and has an uneven surface;
The inorganic powder is contained in an amount of 35% by mass to 70% by mass based on the total amount of the thermoplastic resin and the inorganic powder,
The inorganic powder is at least one of diatomaceous earth and zeolite (excluding the microbial carrier containing a hydrophilizing agent for cellulose-based powder). 2. The submersible microorganism carrier according to claim 1, characterized in that the submersible microorganism carrier has a specific surface area of 1 m ² /g to 5 m ² /g. A method for producing the underwater microbial carrier according to claim 1 or 2, comprising the steps of:
A method for producing an underwater microorganism carrier, comprising kneading at least the thermoplastic resin, the inorganic powder and a foaming agent, and foam-molding the mixture. 4. The method for producing an underwater microorganism carrier according to claim 3, characterized in that the raw materials other than the foaming agent are pelletized in advance, the pellets are mixed with the foaming agent, and extrusion foaming is performed.

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