Microorganism carrier and method for producing microorganism carrier

Abstract

This invention provides a microorganism carrier excellent in carrying ability and a method for producing same. This invention relates to a microorganism carrier comprising a support containing thermoplastic resin and a surface modification layer containing a copolymer containing two or more monomers, the content ratio of the thermoplastic resin being 60-100 mass% with respect to the total mass of the support, the content ratio of the copolymer being 60-100 mass% with respect to the total mass of the surface modification layer.

Description

Microbial carrier and method for producing a microbial carrier

[0001] This invention relates to a microbial carrier and a method for producing a microbial carrier.

[0002] Due to global climate change, the demand for safe water that ecosystems need is increasing. In order to stably supply safe water, it is essential to develop water treatment technologies that not only draw water from natural sources but also purify and reuse used water, and various studies are being conducted on water treatment technologies. For example, Patent Document 1 proposes a method to improve the efficiency of water treatment by utilizing the coexistence and cooperative action of aerobic and anaerobic microorganisms, bringing water and microorganisms into contact in a reaction vessel via a porous or fibrous material, and maintaining an oxygen concentration gradient.

[0003] Japanese Patent Application Publication No. 01-281198

[0004] However, conventional microbial carriers did not have sufficient carrying capacity, and as a result, their water treatment capacity was also insufficient.

[0005] This invention has been made in view of the above-mentioned problems, and aims to provide a microbial carrier with excellent carrying capacity, and a method for producing a microbial carrier.

[0006] As a result of diligent research to solve the above problems, the present inventors have found that the above problems can be solved by providing a support containing a thermoplastic resin and a surface modification layer containing a copolymer containing two or more monomers, and by keeping the content ratio of the thermoplastic resin and the copolymer within a predetermined range, thus completing the present invention.

[0007] In other words, the present invention includes the following embodiments of a microbial carrier and a method for producing a microbial carrier: [1] A microbial carrier comprising a support containing a thermoplastic resin and a surface modification layer containing a copolymer containing two or more monomers, wherein the content of the thermoplastic resin is 60% by mass or more and 100% by mass or less with respect to the total mass of the support, and the content of the copolymer is 60% by mass or more and 100% by mass or less with respect to the total mass of the surface modification layer. [2] The microbial carrier according to [1], used as a fluid filter material. [3] The microbial carrier according to [1] or [2], wherein the monomer is one or more selected from the group consisting of acrylic acid esters, acrylamides, and unsaturated carboxylic acids. [4] The microbial carrier according to any one of [1] to [3], wherein the monomer is an acrylic acid ester. [5] The copolymer comprises a first monomer comprising one or more selected from the group consisting of behenyl acrylate, behenyl methacrylate, stearyl acrylate, stearyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, lauryl acrylate, and lauryl methacrylate, and a second monomer comprising one or more selected from the group consisting of acrylic acid, methacrylic acid, 2-(dimethylamino)ethyl acrylate, 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl acrylate, 2-(diethylamino)ethyl methacrylate, 2-(tert-butylamino)ethyl acrylate, 2-(tert-butylamino)ethyl methacrylate, diethylene glycol monoethyl ether acrylate, diethylene glycol monoethyl ether methacrylate, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dimethylaminopropylacrylamide, and N-tert-butylacrylamide. A microbial carrier according to any one of [1] to [4]. [6] The microbial carrier according to [5], wherein the copolymer is a block copolymer and the weight-average molecular weight of the block of the first monomer is 2000 or more.[7] The microbial carrier according to any one of [1] to [6], wherein the thermoplastic resin comprises one or more selected from the group consisting of high-density polyethylene, ultra-high molecular weight polyethylene, and polystyrene resin. [8] The microbial carrier according to any one of [1] to [7], wherein the supported microorganism is a bacterium. [9] The microbial carrier according to any one of [1] to [8], wherein a microorganism is supported in the surface modification layer.

[10] A method for producing a microbial carrier comprising a support containing a thermoplastic resin and a surface modification layer containing a copolymer containing two or more monomers, comprising: a mixing step of mixing the copolymer and an organic solvent to make a surface modification composition; an immersion step of immersing the support in the heated surface modification composition; and a drying step of evaporating the organic solvent on the surface of the support after the immersion step to obtain a surface-modified support.

[11] A method for producing a microorganism carrier according to

[10] , further comprising a supporting step of placing the surface-modified support in an aqueous solution containing microorganisms to support the microorganisms on the surface-modified layer.

[0008] According to the present invention, it is possible to provide a microbial carrier with excellent microorganism-carrying ability, and as a result, a microbial carrier with excellent water treatment ability, as well as a method for producing the same.

[0009] This figure shows an example of the shape of a microbial carrier. This is a graph showing the measurement results of ammonium concentration and nitrite concentration. This is Table 1 showing the measurement results of ammonium concentration and nitrite concentration. This is a graph showing the measurement results of ammonium concentration and nitrite concentration. This is Table 2 showing the measurement results of ammonium concentration and nitrite concentration. This is a graph showing the measurement results of ammonium concentration and nitrite concentration. This is Table 3 showing the measurement results of ammonium concentration and nitrite concentration.

[0010] The following describes in detail embodiments of the present invention (hereinafter referred to as "these embodiments"), but the present invention is not limited thereto, and various modifications are possible without departing from its essence. In the drawings, the same elements are denoted by the same reference numerals, and redundant explanations are omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Moreover, the dimensional ratios in the drawings are not limited to those shown.

[0011] In recent years, in order to supply safe water, the development of water treatment technologies that not only draw water from natural sources but also purify and reuse used water has become increasingly important. In fields such as ornamental fish farming and hydroponics, various methods are being considered to stabilize and maintain water quality. For example, a technology is known that uses a carrier capable of supporting microorganisms to remove impurities and harmful substances from water through biological filtration. However, the carrying capacity of such microbial carriers has not yet been sufficient.

[0012] As a result of diligent research on this point, the present invention has found that the microbial carrier's carrying capacity is improved when the microbial carrier comprises a support containing a thermoplastic resin and a surface modification layer containing a copolymer containing two or more monomers, wherein the content of the thermoplastic resin is 60% to 100% by mass relative to the total mass of the support, and the content of the copolymer is 60% to 100% by mass relative to the total mass of the surface modification layer. The reason why such a microbial carrier has excellent carrying capacity is thought to be that by surface modifying the support containing a predetermined amount or more of thermoplastic resin with a surface modification layer containing a predetermined amount or more of copolymer, the functional groups on the surface of the copolymer have a high affinity for microorganisms, making it easier for them to adhere to the carrier and grow, resulting in improved carrying capacity. However, the factors are not limited to those described above.

[0013] In this specification, "microbial carrier" refers to a material capable of carrying microorganisms, regardless of whether microorganisms are actually carried on it. Since such microbial carriers have the ability to carry organisms or cells, they can also be described as biological reproduction substrates or cell fixation substrates.

[0014] The microbial carrier of this embodiment and its manufacturing method will be described in detail below.

[0015] 1. Microbial carrier The microbial carrier of this embodiment (hereinafter also simply referred to as "microbial carrier") comprises a support containing a thermoplastic resin and a surface modification layer containing a copolymer comprising two or more monomers that covers the surface of the support, wherein the content of the thermoplastic resin is 60% by mass or more and 100% by mass or less with respect to the total mass of the support, and the content of the copolymer is 60% by mass or more and 100% by mass or less with respect to the total mass of the surface modification layer.

[0016] Such microbial carriers have excellent microbial carrying capacity and therefore also have excellent water purification capabilities using microorganisms, making them preferable for use as fluidized bed filters. Furthermore, when using the microbial carrier of this embodiment as a fluidized bed filter, it is assumed to be used at water temperatures (0 to 30°C), and is superior because of its high microbial carrying capacity and minimal shedding of carried microorganisms. Moreover, the microbial carrier of this embodiment has such high adsorption strength that the surface modification layer does not detach from the support even after standing for one hour in 80°C water or 70°C ethanol.

[0017] The shape of the microbial carrier or support is not particularly limited and includes, for example, plate-shaped, rod-shaped, cylindrical, spherical, rectangular parallelepiped, other block-shaped, sheet-shaped, film-shaped, fibrous, or porous membrane. Among the various shapes, from the viewpoint of further improving the ability to carry microorganisms, it is preferable to use a shape that has a large specific surface area, and a porous shape is preferred. Figure 1 shows an example of the shape of the microbial carrier or support. As shown in Figure 1, by using a shape with many holes, the ability to carry microorganisms and the water purification ability can be further improved.

[0018] 1.1. Support The support of this embodiment contains thermoplastic resin in an amount of 60% to 100% by mass relative to the total mass of the support. That is, the support mainly consists of thermoplastic resin. By using a support mainly composed of thermoplastic resin, the bonding strength with the surface modification layer is improved, and the ability to support microbial carriers is improved. From a similar viewpoint, the content of thermoplastic resin in the support is preferably 65% ​​to 100% by mass, more preferably 70% to 100% by mass, even more preferably 90% to 100% by mass, and even more preferably the support is made of thermoplastic resin.

[0019] Examples of thermoplastic resins include polyolefin resins, polystyrene resins, vinyl resins, polyamide resins, polyacrylic resins, polyester resins, or copolymers thereof. From the viewpoint of more effectively and reliably achieving the load-bearing capacity improvement effect of the present invention, it is preferable to include one or more selected from the group consisting of polyolefin resins, polystyrene resins, vinyl resins, polyamide resins, and polyacrylic resins, and it is more preferable to include at least one of polyolefin resins or polystyrene resins. More specifically, it is even more preferable to include one or more selected from the group consisting of high-density polyethylene, ultra-high molecular weight polyethylene, and polystyrene resins, and it is even more preferable to include high-density polyethylene, ultra-high molecular weight polyethylene, or polystyrene resin.

[0020] Examples of polyolefin resins include high-density polyethylene (HDPE), ultra-high molecular weight polyethylene, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene, or mixtures thereof. From the viewpoint of achieving the load-bearing capacity improvement effect of the present invention more effectively and reliably, at least one of high-density polyethylene (HDPE) or ultra-high molecular weight polyethylene is preferred, and high-density polyethylene (HDPE) is more preferred.

[0021] In this embodiment, high-density polyethylene refers to polyethylene with a density of 0.945 to 1.011 g / cm³. ３This refers to a material that is as described above. High-density polyethylene is not particularly limited, but examples include homopolymers of ethylene, or copolymers of ethylene with other α-olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene. The MFR (melt flow rate; ASTM D 1238, load 2160 g, temperature 190°C) of high-density polyethylene is preferably 0.1 to 50 g / 10 min, and more preferably 0.2 to 35 g / 10 min.

[0022] In this embodiment, ultra-high molecular weight polyethylene refers to polyethylene whose intrinsic viscosity (IV), measured in a decalin solution at 135°C, is preferably 5 dl / g or more, more preferably 10 dl / g or more, and even more preferably 15 dl / g or more. The upper limit of the intrinsic viscosity of ultra-high molecular weight polyethylene is not particularly limited, but is preferably 100 dl / g or less, more preferably 90 dl / g or less, and even more preferably 80 dl / g or less.

[0023] In this embodiment, low-density polyethylene refers to polyethylene with a density of 0.945 g / cm³. ３ This refers to materials that are less than [a certain value]. Low-density polyethylene is not particularly limited, but examples include homopolymers of ethylene, or copolymers of ethylene with other α-olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene.

[0024] The specific surface area of ​​the support or microbial carrier is set to 100 cm² from the viewpoint of further improving the microbial carrying capacity while ensuring fluidity. ２ Preferably, it is 1 / g or more, and 500 cm ２ It is more preferable to be 1000 cm² or more. ２ It is even more preferable if it is 1 / g or more. The upper limit of the specific surface area of ​​the support or microbial carrier is 10,000 cm², from the same viewpoint as above. ２ Preferably, it is less than or equal to 4000 cm². ２ It is more preferable if the amount is less than or equal to / g.

[0025] The specific gravity of the support or microbial carrier is preferably 0.80 or higher, more preferably 0.90 or higher, and even more preferably 0.94 or higher, from the viewpoint of ensuring fluidity while further improving the ability to support microorganisms. The upper limit of the specific gravity of the support or microbial carrier is preferably 1.10 or lower, and more preferably 1.00 or lower.

[0026] The opening ratio of the support or microbial carrier relative to its total volume is preferably 60% or more, more preferably 75% or more, and even more preferably 85% or more, from the viewpoint of ensuring fluidity while further improving the ability to support microorganisms. The upper limit of the opening ratio of the support or microbial carrier is preferably 98% or less, and more preferably 95% or less.

[0027] The support may contain components other than those described above, as needed. Such other components include, but are not limited to, plasticizers, stabilizers, colorants, fillers, antistatic agents, and lubricants.

[0028] 1.2. Surface Modification Layer The surface modification layer of this embodiment contains a copolymer comprising two or more monomers, and the copolymer content is 60% by mass or more and 100% by mass or less relative to the total mass of the surface modification layer. By providing a microbial carrier with such a surface modification layer, the carrier capacity is improved, and as a result, the water purification capacity is also excellent. From a similar viewpoint, the copolymer content is preferably 65% ​​by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and it is even more preferable if the surface modification layer consists of the above copolymer.

[0029] The surface modification layer is formed on the surface of the support by covering it with a surface modification composition. Specifically, the surface modification composition forms a copolymer coating layer on the surface, covering the support. The surface modification composition may contain two or more monomers, an organic solvent, etc. The monomers include at least two types: a first monomer and a second monomer. The following describes in detail each component that may be included in the surface modification composition used to form the surface modification layer.

[0030] 1.2.1. First monomer of copolymer The first monomer is not particularly limited, but is preferably a monomer having a polymerizable unsaturated bond. Examples of such monomers include vinyl monomers, diene monomers, acetylene monomers, cyclic olefin monomers, etc. From the viewpoint of achieving the effect of improving the carrying capacity according to the present invention more effectively and reliably, vinyl monomers having a vinyl group are preferred.

[0031] The first monomer is preferably one or more selected from the group consisting of acrylic acid esters, acrylamides, and unsaturated carboxylic acids, and more preferably an acrylic acid ester. By using such a monomer as the first monomer, the effect of improving the loading capacity according to the present invention tends to be achieved more effectively and reliably.

[0032] Examples of acrylic acid esters include behenyl acrylate, behenyl methacrylate, stearyl acrylate, stearyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, myristyl acrylate, myristyl methacrylate, lauryl acrylate, and lauryl methacrylate. Among these, one or more selected from the group consisting of behenyl acrylate, behenyl methacrylate, stearyl acrylate, stearyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, lauryl acrylate, and lauryl methacrylate are preferred. Using such a first monomer tends to make the load-bearing capacity improvement effect of the present invention more effective and reliable. From a similar viewpoint, the first monomer is more preferably behenyl acrylate or stearyl methacrylate. The first monomer may be used alone or in combination of two or more.

[0033] The content of the first monomer constituting the copolymer (copolymerization ratio) is preferably 5% by mass or more and 95% by mass, and more preferably 10% by mass or more and 90% by mass or less, relative to the total amount of the copolymer. When the content of the first monomer is within the above range, the carrying capacity of the microbial carrier tends to improve.

[0034] The weight-average molecular weight of the first monomer block constituting the copolymer is preferably 2000 or more, and more preferably 3000 or more. There is no particular upper limit to the weight-average molecular weight of the first monomer constituting the copolymer, but it is 100,000 or less. When the weight-average molecular weight of the first monomer constituting the copolymer is 2000 or more, i.e., the length of the long-chain alkane chain portion that can contribute to entanglement increases, the number of bonds originating from cocrystal interactions tends to increase. This allows the copolymer to exhibit compatibility and bonding properties with the support. The method for measuring the weight-average molecular weight of the first monomer is not particularly limited as long as it is a conventionally known method, but for example, it can be measured by GPC after the polymerization of the first monomer block is complete and before the polymerization of the second monomer block begins.

[0035] 1.2.2. Second monomer of copolymer The second monomer is preferably polar. By using a polar monomer, the effect of improving the support capacity according to the present invention tends to be more effective and reliable. From a similar viewpoint, the second monomer is preferably a monomer having a polymerizable unsaturated bond with any of the following: an amino group, an amide group, a hydroxyl group, an alkoxy group, a carboxyl group, an epoxy group, or an ether group. More specifically, vinyl monomers are examples of such monomers.

[0036] More specifically, the second monomer preferably contains one or more selected from the group consisting of acrylic acid, methacrylic acid, 2-(dimethylamino)ethyl acrylate, 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl acrylate, 2-(diethylamino)ethyl methacrylate (DEAEMA), 2-(tert-butylamino)ethyl acrylate, 2-(tert-butylamino)ethyl methacrylate (TBAEMA), diethylene glycol monoethyl ether acrylate (DEEA), diethylene glycol monoethyl ether methacrylate, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dimethylaminopropylacrylamide, and N-tert-butylacrylamide. Using these as the second monomer tends to make the load-bearing capacity improvement effect of the present invention even more effective and reliable. From a similar viewpoint, one or more selected from the group consisting of 2-(diethylamino)ethyl methacrylate (DEAEMA), 2-(tert-butylamino)ethyl methacrylate (TBAEMA), and diethylene glycol monoethyl ether acrylate (DEEA) is more preferred, and 2-(diethylamino)ethyl methacrylate (DEAEMA), 2-(tert-butylamino)ethyl methacrylate (TBAEMA), or diethylene glycol monoethyl ether acrylate (DEEA) is even more preferred. The second monomer may be used alone or in combination of two or more.

[0037] The content of the second monomer constituting the copolymer (copolymerization ratio) is preferably 5% by mass or more and 95% by mass, and more preferably 10% by mass or more and 90% by mass or less, relative to the total amount of the copolymer. When the content of the second monomer is within the above range, the carrying capacity of the microbial carrier tends to improve.

[0038] The weight-average molecular weight of the block of the second monomer constituting the copolymer is preferably 2000 or more, more preferably 3000 or more. The upper limit of the weight-average molecular weight of the second monomer constituting the copolymer is not particularly limited, but is 100000 or less. When the weight-average molecular weight of the second monomer constituting the copolymer is 2000 or more, that is, the long-chain alkane chain moiety that can contribute to entanglement becomes longer, the bonds derived from the co-crystalline interaction tend to increase. Thereby, the compatibility and binding property of the copolymer with respect to the support are exhibited. The method for measuring the weight-average molecular weight of the second monomer is not particularly limited as long as it is a conventionally known method.

[0039] The content of the copolymer is preferably 20.0% by mass or less, more preferably 15.0% by mass or less, still more preferably 10.0% by mass or less, even more preferably 5.0% by mass or less, still more preferably 3.0% by mass or less, and particularly preferably 1.0% by mass or less with respect to the total amount of the surface-modifying composition. When the content of the copolymer is 10.0% by mass or less, the uniformity of the copolymer in the obtained microorganism carrier tends to be further improved, and the mechanical properties tend to be further improved. The lower limit of the content of the copolymer in the surface-modifying composition is preferably 0.003% by mass or more, more preferably 0.01% by mass or more, and still more preferably 0.1% by mass or more. When the content of the copolymer is 0.003% by mass or more, the loading capacity of the obtained microorganism carrier tends to be further improved.

[0040] Further, the content of the copolymer is preferably 0.001% by mass or more and 30% by mass or less, more preferably 0.01% by mass or more and 10% by mass or less, still more preferably 0.01% by mass or more and 5% by mass or less, and particularly preferably 0.1% by mass or more and 3% by mass or less with respect to the total amount of the thermoplastic resin contained in the support. When the content of the copolymer with respect to the total amount of the thermoplastic resin is 0.001% by mass or more, the surface-modifying property of the obtained microorganism carrier tends to be further improved. Also, when the content of the copolymer with respect to the total amount of the thermoplastic resin is 5% by mass or less, the mechanical properties of the obtained microorganism carrier tend to be further improved.

[0041] 1.2.3. The organic solvent used in the composition for surface modification of the organic solvent is not particularly limited as long as it can dissolve the thermoplastic resin and the above copolymer. For example, at least one selected from the group consisting of halogen-based solvents, ether-based solvents, ketone-based solvents, aromatic solvents, alkane-based solvents, cycloalkane-based solvents, dicycloalkane-based solvents, and nitro-based solvents can be mentioned. Among these, aromatic solvents are preferred. By using such a solvent, in the method for producing a microorganism carrier described later, the compatibility of the thermoplastic resin and the copolymer is further improved, and surface modification is more stably performed, resulting in a tendency for the loading capacity to be improved. The organic solvent used in the present embodiment may be a mixed solvent in which a plurality of solvents are mixed.

[0042] The halogen-based solvent is not particularly limited. For example, chlorotoluene (162 ° C), monochlorobenzene (131 ° C), dichlorobenzene (180 ° C), perchloroethylene (121 ° C), and tetrachloroethane (146 ° C) can be mentioned. The ether-based solvent is not particularly limited. For example, dibutyl ether (142 ° C) can be mentioned. Further, the ketone-based solvent is not particularly limited. For example, diisopropyl ketone (125 ° C) can be mentioned. The aromatic solvent is not particularly limited. For example, ethylbenzene (136 ° C) and tetralin (207 ° C) can be mentioned. Further, the alkane-based solvent is not particularly limited. For example, octane (126 ° C) can be mentioned. The cycloalkane-based solvent is not particularly limited. For example, cycloheptane (118 ° C) and cyclooctane (149 ° C) can be mentioned. Further, the dicycloalkane-based solvent is not particularly limited. For example, decalin (186 ° C) can be mentioned. The nitro-based solvent is not particularly limited. For example, nitrobenzene (210 ° C) can be mentioned.

[0043] The boiling point of the organic solvent is preferably 100°C or higher, more preferably 120°C or higher, even more preferably 130°C or higher, and particularly preferably 140°C or higher. A boiling point of 100°C or higher allows the thermoplastic resin and copolymer to be mixed at a relatively high temperature, which in the method for producing the microbial carrier described later tends to improve the compatibility of the thermoplastic resin and copolymer and to more stably exhibit the effect of improving the carrying capacity. Furthermore, while there is no particular upper limit to the boiling point of the organic solvent, 250°C or lower is preferred. A boiling point of 250°C or lower tends to cause the solvent to volatilize more easily in the method for producing the microbial carrier described later. In this embodiment, the boiling point refers to the temperature measured under atmospheric pressure.

[0044] The content of the organic solvent is preferably 30% to 98% by mass, more preferably 40% to 95% by mass, and even more preferably 50% to 90% by mass, based on the total amount of the liquid composition for surface modification. When the organic solvent content is 30% by mass or more, the viscosity of the liquid composition for surface modification tends to decrease, and moldability tends to improve. Also, when the organic solvent content is 98% by mass or less, the amount of solvent to be evaporated decreases, and manufacturing costs tend to be reduced. The optimal range for the organic solvent content can be appropriately changed depending on the target microbial carrier and the molding method for molding it.

[0045] In addition to the components described above, the surface modification composition may also contain other components, such as known plasticizers, heat stabilizers, colorants, organic lubricants, inorganic lubricants, surfactants, and processing aids.

[0046] 1.3. Microorganisms The microbial carrier of this embodiment tends to exhibit the water purification capacity according to the present invention more effectively and reliably when microorganisms are supported on the surface modification layer. Bacteria are preferred as the microorganisms that the microbial carrier can support. If a microbial carrier supporting bacteria is used as a fluid filter material, an improvement in purification capacity can be expected. The bacteria are not particularly limited, but examples include nitrifying bacteria, heterotrophic bacteria, denitrifying bacteria, methane-producing bacteria, sulfate-reducing bacteria, etc., and nitrifying bacteria and denitrifying bacteria are preferred. As commercially available microorganisms, for example, Samurai EX (product name, manufactured by Bacteria Honpo Co., Ltd.) and Super Biocom 78 (product name, for freshwater use only, manufactured by Biocom Co., Ltd.) can be preferably used.

[0047] 2. Method for Producing a Microbial Carrier The method for producing a microbial carrier according to this embodiment (hereinafter also referred to as "this production method") is a method for producing a microbial carrier comprising a support containing a thermoplastic resin and a surface modification layer containing a copolymer containing two or more monomers, comprising: a mixing step of mixing the copolymer and an organic solvent to make a surface modification composition; an immersion step of immersing the support in the heated surface modification composition; and a drying step of evaporating the organic solvent on the surface of the support after the immersion step to obtain a surface-modified support. The microbial carrier obtained by this production method has excellent carrying capacity.

[0048] The support material can be any material mainly composed of thermoplastic resin, and may be a commercially available material or one manufactured by a known method. Known manufacturing methods include, for example, extrusion molding, injection molding, blow molding, and compression molding. From the viewpoint of achieving the effect of improving the load-carrying capacity according to the present invention more effectively and reliably, the extrusion molding method is preferred.

[0049] 2.1. Mixing Step The mixing step is a step of preparing a surface modification composition by mixing a copolymer containing two or more monomers with an organic solvent. The types of compounds that may be included in the surface modification composition, particularly the monomers of the copolymer and the organic solvent, and the manner of use are preferably the same as described above.

[0050] 2.2. Immersion Process The immersion process involves immersing the support in a heated surface modification composition. The method for immersing the support in the heated surface modification composition may involve preheating the surface modification composition before immersing the support, or immersing the support in the surface modification composition or applying the surface modification composition to the support while it is heated, thereby bringing the temperature of the surface modification composition within the above range.

[0051] In the immersion process, heating the surface modification composition is necessary to further improve the adsorption strength of the surface modification layer to the support surface. The lower limit of the heating temperature range is preferably above a temperature about 60°C lower than the melting point of the thermoplastic resin constituting the support. The upper limit of the temperature range is preferably below the melting point of the thermoplastic resin. From this viewpoint, the temperature range of the surface modification composition in the immersion process is preferably 50°C to 130°C, more preferably 55°C to 120°C, and even more preferably 60°C to 110°C.

[0052] The immersion time of the support is not particularly limited, but is preferably 0.1 seconds to 60 minutes, more preferably 0.5 seconds to 50 minutes, and even more preferably 10 seconds to 30 minutes. By setting the immersion time within this range, the effect of improving the support capacity according to the present invention tends to be achieved more effectively and reliably.

[0053] 2.3. Drying Process The drying process is a step in which the organic solvent on the surface of the support is evaporated after the immersion process to obtain a surface-modified support. The drying method is not particularly limited and examples include hot air drying, reduced pressure drying, infrared drying, and natural drying. From the viewpoint of achieving the effects of the present invention more effectively and reliably, natural drying is preferred.

[0054] In the drying process in which the organic solvent is volatilized from the surface modification composition, the solid content (non-volatile content) contained in the composition is gradually concentrated, and ultimately a surface modification layer mainly composed of copolymer is obtained. In this process, it is thought that the molecular chains of the copolymer constituting the surface of the support become entangled with each other so that the portion mainly consisting of the first monomer of the copolymer (hereinafter also referred to as the "first constituent part") is incorporated into the crystalline region of the copolymer molecular chains, and that they bond together to form a cocrystal (hereinafter also referred to as the "cocrystal interaction"). Conceptually, in order for such a cocrystal interaction, which requires molecular chain entanglement, to be exhibited, there are necessary stages: a stage in which the molecular chains are unraveled to the extent that they can entangle, a stage in which the unraveled molecular chains become entangled, and a stage in which the entangled molecular chains form a cocrystal. It is thought that these stages proceed sequentially as the solvent volatilizes.

[0055] Furthermore, the portion mainly consisting of a polar second monomer is less likely to be incorporated into the entanglement of these molecular chains, and is therefore likely to be exposed on the surface of the surface modification layer, for example. Therefore, the surface modification layer obtained by volatilizing the solvent from the above surface modification composition contains a copolymer in which the first component acts as an anchor and is incorporated into the thermoplastic resin, while the portion mainly consisting of a second monomer with reactive functional groups is positioned outside the cocrystal interaction region, particularly on the surface of the surface modification layer. Thus, according to the surface modification composition of this embodiment and the process of forming a surface modification layer using it, the surface of the support, which is considered to have poor affinity for microorganisms, can be modified according to the properties of the second monomer, and the affinity of the surface modification layer for microorganisms is improved. In addition to improved affinity for microorganisms, this surface modification also has effects such as improved adhesive strength when bonded with an adhesive and improved dyeability when dyed. However, the mechanism by which the effects of this embodiment are achieved is not limited to the above.

[0056] 2.4. Loading Step This manufacturing method preferably further includes a loading step of placing the surface-modified support in an aqueous solution containing microorganisms to load the microorganisms onto the surface-modified layer. After loading the microorganisms, the microorganism-loaded support can be used for water purification treatment, such as using it as a cross-flow filtration medium.

[0057] In the loading step, the loading period is preferably 2 days or more. By performing the loading step for 2 days or more, the amount of microorganisms loaded increases sufficiently, and the effect of water purification treatment tends to be further improved. From the same perspective, the period of the loading step is more preferably 10 days or more, even more preferably 30 days or more, even further preferably 3 months or more, and particularly preferably 6 months or more. Also, the period of the loading step may be, for example, 5 years or less, or 3 years or less. In this specification, performing the loading step for 3 months or more is also referred to as aging or an aging process. When the aging process is performed, the desorption of microorganisms from the support is suppressed, and the stability of water purification treatment tends to be further improved.

[0058] Hereinafter, this embodiment will be described more specifically using examples and comparative examples. This embodiment is not limited in any way by the following examples.

[0059] (Test A) 1. Preparation of Microorganism-Loaded Support 1.1. Preparation of Support A material made of high-density polyethylene (product name "Novatec HD HJ560", manufactured by Nippon Polyethylene Co., Ltd., density 0.964 g / cm ３ , melting point 135 °C) was prepared. Next, the high-density polyethylene material was put into an extruder, melted while heating to 180 °C, extruded with a screw, and extruded through a die having a shape with a large number of gaps. The extruded high-density polyethylene molded body was immediately cooled and solidified at 20 °C, and then cut into pieces with a thickness of 4 mm by a cutter to obtain a support having a surface shape with a large number of gaps as shown in FIG. 1. The support had a shape of a disk with a diameter of 25 mm and a thickness of 4 mm, with 64 holes drilled, and its density was 0.96 g / cm ２ , and the specific surface area was 1200 m ２ / m ３ . Also, the aperture ratio (porosity) of the obtained support was 90%.

[0060] 1.2. Formation of Surface Modification Layer 1.2.1. Preparation of Surface Modification Composition 1 5.0 g of stearyl acrylate, 5.0 g of butyl acetate, and 0.38 g of BlockBuilder MA (manufactured by ARKEMA) (initiator) were placed in a stirring polymerization apparatus, and the atmosphere inside the apparatus was replaced with a nitrogen atmosphere. Polymerization was then carried out for 24 hours while heating in an oil bath (110°C). Next, 5.0 g of 2-(diethylamino)ethyl methacrylate and 5.0 g of butyl acetate were further added to the stirring polymerization apparatus, and polymerization was carried out for 24 hours while heating in an oil bath (110°C). After polymerization, the reaction solution was added dropwise to methanol to precipitate the block copolymer of stearyl acrylate and 2-(diethylamino)ethyl methacrylate, and copolymer 1 (STA-DEAEMA) was obtained by filtering the precipitate. 0.001 g of the obtained copolymer 1 was mixed with 10 g of high-density polyethylene (product name "FX201A", manufactured by Keiyo Polyethylene Co., Ltd.) and 89.999 g of decalin to obtain surface modification composition 1. The weight-average molecular weight of the stearyl acrylate block in copolymer 1 was 10,000.

[0061] 1.2.2. Preparation of Surface Modification Composition 2 5.0 g of behenyl acrylate, 5.0 g of butyl acetate, and 0.38 g of BlockBuilder MA (manufactured by ARKEMA) (initiator) were placed in a stirring polymerization apparatus, and the atmosphere inside the apparatus was replaced with a nitrogen atmosphere. Polymerization was then carried out for 24 hours while heating in an oil bath (110°C). Next, 5.0 g of 2-(tert-butylamino)ethyl methacrylate and 5.0 g of butyl acetate were further added to the stirring polymerization apparatus, and polymerization was carried out for 24 hours while heating in an oil bath (110°C). After polymerization, the reaction solution was added dropwise to methanol to precipitate the block copolymer of behenyl acrylate and 2-(tert-butylamino)ethyl methacrylate, and copolymer 2 (BHA-TBAEMA) was obtained by filtering the precipitate. 0.35 g of the obtained copolymer 2 was mixed with 349.65 g of xylene to obtain surface modification composition 2 (0.1% by mass). The weight-average molecular weight of the behenyl acrylate block in copolymer 2 was 10,000.

[0062] 1.2.3. Preparation of Surface Modification Composition 3 5.0 g of stearyl acrylate, 5.0 g of butyl acetate, and 0.38 g of BlockBuilder MA (manufactured by ARKEMA) (initiator) were placed in a stirring polymerization apparatus, and the atmosphere inside the apparatus was replaced with a nitrogen atmosphere. Polymerization was then carried out for 24 hours while heating in an oil bath (110°C). Next, 5.0 g of di(ethylene glycol) ethyl ether acrylate (DEEA) and 5.0 g of butyl acetate were further added to the stirring polymerization apparatus, and polymerization was carried out for 24 hours while heating in an oil bath (110°C). After polymerization, the reaction solution was added dropwise to methanol to precipitate the block copolymer of stearyl acrylate and di(ethylene glycol) ethyl ether acrylate, and copolymer 3 (STA-DEEA) was obtained by filtering the precipitate. 0.35 g of the obtained copolymer 3 was mixed with 349.65 g of xylene to obtain surface modification composition 3 (0.1% by mass). The weight-average molecular weight of the stearyl acrylate block in copolymer 3 was 10,000. The weight-average molecular weight in all examples was measured using an HLC-8320 GPC (GPC instrument, manufactured by Tosoh Corporation).

[0063] 1.2.4. Surface Modification Each of the surface modification compositions obtained above was heated to 100°C, and the support was placed in it and immersed for 10 minutes. After that, it was immediately removed and cooled to 25°C at a rate of 25°C / sec (immersion step). After cooling, the immersed support was removed and air-dried to obtain the microbial carrier of the present invention (drying step). In the following description, the microbial carrier modified with surface modification composition 1 was used in Examples 1 and 4, the microbial carrier modified with surface modification composition 2 was used in Examples 2 and 5, and the microbial carrier modified with surface modification composition 3 was used in Examples 3 and 6.

[0064] 2. Changes in ammonium and other concentrations due to shrimp ecology 2.1. Aquarium setup (Sets 1-4) 35 L of tap water was mixed with 7 mL of dechlorinator (product name "GEX Chlorine Off", a fast-acting dechlorinator containing potassium to neutralize chlorine and chloramine, manufactured by GEX Corporation) and poured into aquarium A for fluid filtration. Three circulation pumps, one heater, and one aeration device were installed in aquarium A. The water temperature was maintained at 28°C with the heater, while the aeration and circulation pumps maintained the stirring action in the aquarium. 40 mL of Samurai EX (product name, manufactured by Bacteria Honpo Co., Ltd.) and 110 mL of Super Biocom 78 (product name, for freshwater use only, manufactured by Biocom Co., Ltd.) were added to aquarium A as bacteria, and 2.5 mL of Biocom 78 (product name, substrate for nitrifying bacteria, manufactured by Biocom Co., Ltd.) was added. In addition, 2 mL of APT EI (product name, liquid fertilizer, manufactured by THE 2HR AQUARIST) was added as the initial nitrogen source. Furthermore, separately from tank A, 15 L of tap water with 3 mL of dechlorinator added was poured into tank B, and a bundle of Anacharis (aquatic plant) was also placed in it. Four sets of such tank A and tank B were prepared, and sets 1 to 3, each containing approximately 8 L of the microbial carrier of the present invention obtained above in tank A, were designated as Examples 1 to 3, while another set 4, in which only the support without a surface modification layer was placed in tank A with approximately 8 L, was designated as Comparative Example 1.

[0065] 2.2. Ammonium and Nitrite Concentrations In sets 1 to 4 obtained above, water was circulated from tank A (for fluid filtration) to tank B using a water pump, and after two days, water quality measurements were started. Immediately afterward, 15 Yamato shrimp were added to tank B of each set, and measurements were continued every 24 hours. WAK-NH4-4 (pack test for ammonium / ammonium nitrogen measurement, manufactured by Kyoritsu Chemical Laboratory) and WAK-NO2 (pack test for nitrite / nitrite nitrogen measurement, manufactured by Kyoritsu Chemical Laboratory) were used to measure water quality.

[0066] The results of measuring ammonium and nitrite concentrations in tank B of sets 1 to 4 are shown in Figure 2 (graph) and Figure 3 (numerical information).

[0067] 2.3. Evaluation Results As shown in Figures 2 and 3, the microbial carrier of the present invention, which comprises a support containing a thermoplastic resin and a surface modification layer containing a copolymer containing two or more monomers, wherein the content of the thermoplastic resin is 60% by mass or more and 100% by mass or less relative to the total mass of the support, and the content of the copolymer is 60% by mass or more and 100% by mass or less relative to the total mass of the surface modification layer, is superior in its ability to support microorganisms compared to the microbial carriers of the comparative example, in that it reduces the ammonium ion concentration and nitrite concentration at an earlier stage.

[0068] 3. Changes in Ammonia Concentration 3.1. Tank Setup (Sets 5-8) 40 L of tap water with 8 mL of the above-mentioned dechlorinator added was poured into Tank C for fluid filtration. The equipment was set up in the same way as in Tank A, and the water temperature was maintained at 28°C with a heater, while aeration and a circulation pump were used to maintain stirring in the tank. 28% ammonia solution (manufactured by Tokyo Chemical Industry Co., Ltd.) was added to Tank C to a concentration of 5 mg / L. Four such Tanks C were prepared, and three of the Tanks C were filled with the microbial carrier of the present invention (used for 30 days) that had been used in "2. Changes in Ammonia Concentration Due to Shrimp Ecology" above. These were designated as Examples 4-6, and one Tank C C was filled with only the support material (used for 30 days) that had been used in "2. Changes in Ammonia Concentration Due to Shrimp Ecology" above. This was designated as Comparative Example 2.

[0069] 3.2. Ammonium and Nitrite Concentrations In the four tanks obtained from Examples 4-6 and Comparative Example 2 above, ammonium and nitrite concentrations were measured. Concentrations were measured every 8 hours until 72 hours had passed, and thereafter every 12 hours. Pack tests described in "2.2. Ammonium and Nitrite Concentrations" were used to measure water quality.

[0070] The results of measuring the ammonium and nitrite concentrations in tank C of Examples 4-6 and Comparative Example 2 are shown in Figures 4 (graph) and 5 (numerical information).

[0071] 3.3. Evaluation Results As shown in Figures 4 and 5, the microbial carrier of the present invention, comprising a support containing a thermoplastic resin and a surface modification layer containing a copolymer containing two or more monomers, wherein the content of the thermoplastic resin is 60% to 100% by mass relative to the total mass of the support, and the content of the copolymer is 60% to 100% by mass relative to the total mass of the surface modification layer, is superior in its ability to support microorganisms compared to the comparative microbial carriers that do not meet these criteria, in that it reduces the ammonium ion concentration and nitrite concentration at an earlier stage. Furthermore, it is presumed that if the microbial carrier supports microorganisms for a long period of time, the ammonium ion concentration and nitrite concentration can be reduced even earlier, and therefore the ability to support microorganisms tends to improve further.

[0072] (Test B) In Test B, the microbial carrier was used for a longer period than the measurement period in "2.2. Ammonium and Nitrite Concentrations" of Test A, and the resulting changes were observed. Below, Test B will be described, focusing on the differences from Test A.

[0073] 1. Preparation of the aquarium: Using a support obtained in the same manner as in Test A, surface modification with the surface modification composition 3 was performed in the same manner as in Test A. The microbial carrier of the present invention obtained in this manner was used in Example 7. In addition, a support obtained in the same manner as in Test A, but without a surface modification layer, was used in Comparative Example 3.

[0074] Two sets similar to those of tanks A and B described above were prepared. One set (set 9) contained approximately 8 liters of the same microbial carrier used in Example 3, placed in tank A, and the other set (set 10) contained approximately 8 liters of a support without a surface modification layer, placed in tank A. In sets 9 and 10, water was circulated from tank A (including the microbial carrier or support) to tank B using a water pump, and the next step was started after two days.

[0075] 2. Fifteen Yamato shrimp and ten medaka were placed in tank B of each of the maturation process sets 9 and 10. They were fed every three days, and 20 liters of water were changed every two weeks, maintaining the setup for six months (maturation). After six months, tank B containing the Yamato shrimp and medaka was separated.

[0076] 3. Confirmation of decomposition rate by maturation process 3.1. Setting up the tanks (Sets 11-12) 40 L of tap water with 8 mL of the above dechlorinator added was poured into tank D for fluid filtration. Each substrate was set up in the same way as in tank A, and the water temperature was maintained at 28°C with a heater, while aeration and a circulation pump were used to maintain stirring in the tank. 28% ammonia water (manufactured by Tokyo Chemical Industry Co., Ltd.) was added to tank D to a concentration of 10 mg / L. Two such tanks D were prepared, and the microbial carrier of the present invention (used for 6 months) that had finished being used in the "2. Maturation Process" described above was placed directly into tank D as Example 7, and only the support material (used for 6 months) that had finished being used in the "2. Maturation Process" described above was placed directly into tank D as Comparative Example 3.

[0077] 3.2. Ammonium and Nitrite Concentrations In the tanks of Example 7 and Comparative Example 3 obtained above, the ammonium and nitrite concentrations were measured. The concentrations were measured at intervals of 6 to 18 hours. Pack tests described in "2.2. Ammonium and Nitrite Concentrations" were used to measure the water quality.

[0078] The results of measuring the ammonium and nitrite concentrations in tank D of Example 7 and Comparative Example 3 are shown in Figures 6 (graph) and 7 (numerical information).

[0079] 4. Evaluation Results As shown in Figures 6 and 7, the microbial carrier of the present invention is superior to the microbial carrier of the comparative example in its ability to reduce ammonium ion concentration and nitrite concentration at an earlier stage. Furthermore, when the microbial carrier undergoes a maturation process to allow for long-term microorganism support, the ammonium ion concentration and nitrite concentration can be reduced even more rapidly, suggesting that the microbial carrier's ability to support microorganisms has further improved.

[0080] Because the microbial carrier of the present invention has excellent ability to support microorganisms, it can be used for microbial water treatment in a wide range of industries that treat water such as water in exhibition tanks, breeding water, sewage, and factory wastewater, and thus has industrial applicability.

[0081] 1. Microbial carrier.

Claims

1. A microbial carrier comprising a support containing a thermoplastic resin and a surface modification layer containing a copolymer comprising two or more monomers, wherein the content of the thermoplastic resin is 60% by mass or more and 100% by mass or less with respect to the total mass of the support, and the content of the copolymer is 60% by mass or more and 100% by mass or less with respect to the total mass of the surface modification layer.

2. The microbial carrier according to claim 1, to be used as a fluidized filter material.

3. The microbial carrier according to claim 1 or 2, wherein the monomer is one or more selected from the group consisting of acrylic acid esters, acrylamides, and unsaturated carboxylic acids.

4. The microbial carrier according to claim 1 or 2, wherein the monomer is an acrylic acid ester.

5. The microbial carrier according to claim 1 or 2, wherein the copolymer comprises a first monomer comprising one or more selected from the group consisting of behenyl acrylate, behenyl methacrylate, stearyl acrylate, stearyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, lauryl acrylate, and lauryl methacrylate; and a second monomer comprising one or more selected from the group consisting of acrylic acid, methacrylic acid, 2-(dimethylamino)ethyl acrylate, 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl acrylate, 2-(diethylamino)ethyl methacrylate, 2-(tert-butylamino)ethyl methacrylate, diethylene glycol monoethyl ether acrylate, diethylene glycol monoethyl ether methacrylate, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dimethylaminopropylacrylamide, and N-tert-butylacrylamide.

6. The microbial carrier according to claim 5, wherein the copolymer is a block copolymer, and the weight-average molecular weight of the block of the first monomer is 2000 or more.

7. The microbial carrier according to claim 1 or 2, wherein the thermoplastic resin comprises one or more selected from the group consisting of high-density polyethylene, ultra-high molecular weight polyethylene, and polystyrene resin.

8. The microorganism carrier according to claim 1 or 2, wherein the supported microorganism is a bacterium.

9. The microbial carrier according to claim 1 or 2, wherein microorganisms are supported in the surface-modified layer.

10. A method for producing a microbial carrier comprising a support containing a thermoplastic resin and a surface modification layer containing a copolymer comprising two or more monomers, comprising: a mixing step of mixing the copolymer and an organic solvent to form a surface modification composition; an immersion step of immersing the support in the heated surface modification composition; and a drying step of evaporating the organic solvent on the surface of the support after the immersion step to obtain a surface-modified support.

11. A method for producing a microbial carrier according to claim 10, further comprising a supporting step of placing the surface-modified support in an aqueous solution containing microorganisms to support the microorganisms on the surface-modified layer.

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