JP2007283222A - Biological treatment carrier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a granular biological treatment carrier which has durability, can be properly floated in an aeration tank, can be utilized in the adhesion of microorganisms at a low cost and is enhanced in sewage purifying capacity. <P>SOLUTION: The biological treatment carrier is constituted of a particulate material comprising a thermoplastic resin having pores with a diameter of 0.1-100 μm and has an apparent density of 0.5-1.5 g/ml and manufactured by forming a granular material, which is obtained by melting and kneading a thermoplastic resin and a particulate inorganic compound, treating the granular material with a solvent, which dissolves the inorganic material but not dissolves the thermoplastic resin, to remove the inorganic material from the granular material and forming pores to the parts where the inorganic compound is not present. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a biological treatment carrier that is put into an aeration tank in order to efficiently remove organic components and nitrogen components contained in sewage by microorganisms.

  In recent years, eutrophication of lakes, inland seas, etc. has progressed due to domestic wastewater and factory wastewater, etc., which causes the occurrence of blue sea urchins and red tides. Technology efficiency is being studied.

  Recently, as a removal technique for high load and high efficiency, particles having a diameter or a side of 3 mm or more (referred to as “support” in this specification) are dispersed and suspended in a treatment tank, and the surface and internal pores of the support are dispersed. A system that decomposes and removes organic components and nitrogen components by high-density microorganisms has attracted attention.

  For example, as a carrier for attaching microorganisms, (1) polyvinyl alcohol gel, (2) polyethylene glycol gel, (3) foamed polypropylene molding, (4) foamed polyurethane molding, (5) polyethylene spherical molding Products, (6) ceramic moldings, (7) fiber masses, bundles, etc. have been proposed, and the materials and shapes have been devised for proper use. These carriers are usually charged into the treatment tank in a volume ratio of 10 to 50% with respect to the sewage, and flow by aerated air from the bottom of the tank and come into contact with the sewage.

  Therefore, these carriers must have good fluidity in water, and should not be damaged by friction or collision between the carriers or the tank wall surface during flow. Furthermore, it is important that there is an area and space where more microorganisms can adhere to the surface and inside of the carrier. Therefore, these carriers have been devised to increase the adhesion area of microorganisms by reducing them to the minimum size that does not flow out of the treatment tank.

  Among these various carriers, gels and polyethylene spherical molded products of polyvinyl alcohol and polyethylene glycol have less voids in the interior than foams and fiber masses, and the adhesion of microorganisms is limited to the surface of the carrier. . In addition, although urethane and polypropylene foams have many pores inside, they are liable to float on the water surface of the treated water tank and have a drawback that the flow in water becomes poor.

  For this reason, a method for making continuous holes has been proposed, but it is relatively easy to make continuous holes in the form of membranes, sheets, and plates. However, these need to be cut into an appropriate size as a carrier as a post-process at the time of production, and it takes time and effort. In addition, since the shape is a rectangular parallelepiped, the corners are removed during use, and the powder flows as a powder, which causes the water quality to deteriorate.

  There is a method using bead foam particles to make a carrier having a spherical shape with continuous pores in one step. However, it is difficult to produce a bead foam having continuous pores, and most of the conventional ones are closed cells. It becomes light and floats on the water surface, so the water purification function is lowered. For this reason, an open-cell foam has been proposed in which a powder that does not melt with the resin forming the carrier is mixed and foamed (Patent Document 1), but it is necessary to add many additives including a foaming agent. For this reason, the manufacturing operation is complicated and the cost is increased. Further, even if the pores are continuous, in the case of a hydrophobic resin, water hardly enters the pores, and as a result, many internal pores cannot be effectively used. In the case of a foam formed of a hydrophobic resin, a method of mixing a hydrophilic resin has also been proposed in order to make it easy for water to enter inside (Patent Document 2), but an incompatible resin is mixed. This is not easy and reproducibility is difficult to obtain.

  On the other hand, in order to produce a support having continuous pores without forming a foam, an inorganic powder and an organic liquid are mixed and melted in a polyolefin resin, and then the inorganic powder and the organic liquid are extracted and removed. A method has been proposed (Patent Document 3). However, this method is not preferable because an organic solvent needs to be used to extract the inorganic powder and the organic liquid.

On the other hand, a fiber lump having a diameter of constituent fibers of several tens of μm or less can obtain an extremely large microbial adhesion effect compared to a granular material because fine fibers form innumerable three-dimensional network structures. (Patent Document 4). However, in this case, it cannot be said that the production method is simple, and the fiber mass may shrink due to heat treatment, and the internal voids may decrease.
JP 2005-171064 A JP 2004-113220 A Japanese Patent Publication No. 60-23130 JP-A-10-180278

  An object of the present invention is to provide a granular biological treatment carrier that is durable, can float appropriately in an aeration tank, can be used for attachment of microorganisms at low cost, and has a high ability to purify sewage. Is.

  As a result of intensive studies to solve the above-mentioned drawbacks, the present inventors are durable, can float appropriately in an aeration tank, and have a high purification capability of sewage that can be used for adhesion of microorganisms at low cost. A granular biological treatment carrier was found and the present invention was completed.

  That is, the biological treatment carrier of the present invention is composed of granules made of a thermoplastic resin having pores having a diameter of 0.1 to 100 μm, and the apparent density is 0.5 to 1.5 g / milliliter. And

  In the method for producing a biological treatment carrier of the present invention, a thermoplastic resin and a powdered inorganic compound are melt-kneaded to form a granular material, and then the granular material is dissolved in the inorganic compound but is thermoplastic. The resin is treated with a solvent that does not dissolve and the inorganic compound is removed from the granular material, thereby forming pores having a diameter of 0.1 to 100 μm in the portion where the inorganic compound was present, and the appearance of the granular material The gist is to set the density to 0.5 to 1.5 grams / milliliter.

  According to the present invention, the biological treatment carrier is composed of granules made of a thermoplastic resin having pores having a diameter of 0.1 to 100 μm, and the apparent density is 0.5 to 1.5 g / milliliter. Since the pore diameter is in the appropriate range, the adherence of microorganisms is good, and the apparent density is in the appropriate range, so that it can float properly in the aeration tank. Can be a high carrier. Further, since the diameter of the hole is 100 μm at the maximum, the hole does not adversely affect the strength of the carrier, and therefore, a carrier having excellent durability can be obtained.

  Further, according to the production method of the present invention, the above-described high-performance carrier can be easily produced at low cost.

  The biological treatment carrier of the present invention is a granular material made of a thermoplastic resin having pores having a diameter of 0.1 to 100 μm and having an apparent density of 0.5 to 1.5 g / milliliter. .

  The thermoplastic resin used for the biological treatment carrier of the present invention is not particularly limited, and examples thereof include general thermoplastic resins. For example, polyethylene, polypropylene, poly-4-methylpentene-1, polybutene, polyisobutylene, polyolefin resin represented by cycloolefin resin, polyamide represented by nylon 6, nylon 66, nylon 46, nylon 11, nylon 12, etc. Resin, polyethylene terephthalate, polybutylene terephthalate, polylactic acid, polybutylene succinate, polyester resin represented by polycarbonate, acrylic resin represented by polymethyl methacrylate, polyacrylic acid, polyacrylonitrile, polyvinyl acetate, In addition to vinyl resins such as polyvinyl alcohol and polyvinyl chloride, mention may be made of fluorine resins, polystyrene resins, acetal resins, polyether resins, silicone resins, etc. Can. These resins may be copolymers or may be partially modified or cross-linked. Among these, polyolefin resins, polyamide resins, and polyester resins are excellent in processability, durability, and cost, and can be preferably used. Particularly preferred are polyethylene, polypropylene and polystyrene, and most preferred are polyethylene and polypropylene.

  The biological treatment carrier of the present invention is a granular material and needs to have pores having a diameter of 0.1 to 100 μm. This makes it easier for microorganisms to adhere and propagate, increasing the water purification capacity. The pores are preferably present not only in the surface portion of the carrier but also in the interior. When the diameter of the holes exceeds 100 μm, the voids become large and the durability of the carrier tends to be poor.

  The granular biological treatment carrier of the present invention needs to have an apparent density of 0.5 to 1.5 grams / milliliter, preferably 0.6 to 1.4 grams / milliliter, and more preferably Is 0.8 to 1.2 grams / milliliter, most preferably 0.9 to 1.1 grams / milliliter. When the apparent density is lower than 0.5 gram / milliliter, the carrier floats in the aeration tank and cannot be processed efficiently. On the other hand, if the apparent density is higher than 1.5 grams / milliliter, the carrier sinks and cannot be processed efficiently.

  The granular biological treatment carrier of the present invention can be preferably produced by melt-kneading a thermoplastic resin and a granular inorganic compound. In the melt kneading, a general kneader such as a single screw extruder, a twin screw extruder, a roll kneader, or a Brabender can be used. In order to disperse the inorganic compound more, a twin screw extruder. Is preferably used. The thermoplastic resin and the inorganic compound may be dry blended and supplied from a hopper, or the inorganic compound may be added from a side feeder.

  The particulate inorganic compound used here is preferably one that is dispersed while maintaining a certain size during melt-kneading with a thermoplastic resin. The mixture of the thermoplastic resin and the inorganic compound thus produced can be used as a processing carrier as it is, but in the present invention, the inorganic compound is removed after melt-kneading to form pores. Thereby, it becomes effective for retention of microorganisms. For this purpose, treatment with a solvent that dissolves the inorganic compound but does not dissolve the thermoplastic resin is performed.

  For this purpose, the inorganic compound is preferably soluble in water. The inorganic compound is removed by water extraction after melt-kneading, but it is not necessary to remove it completely. Therefore, a thing with low toxicity is preferable. In addition, since an inorganic compound that is easily soluble in water has a good affinity with water, a minute amount remains in the resin and can play a role in helping water to enter the carrier.

  Examples of such inorganic compounds include sodium chloride, calcium chloride, magnesium chloride, aluminum chloride, sodium sulfate, magnesium sulfate, calcium sulfate, sodium hydroxide, calcium hydroxide and the like. Of these, sodium chloride and magnesium sulfate are preferred. These inorganic compounds may be amorphous and may not have the same particle size, but those having a certain particle size are preferable. In this case, a preferable average particle diameter is 1 to 100 μm. Although it may be less than 1 μm, it may be bulky and difficult to handle, or it may adsorb extraneous matter such as moisture.

  In addition, although the preferable average particle diameter of a granular inorganic compound is 1-100 micrometers as mentioned above, in the inorganic compound with a smaller average particle diameter, the particle | grains whose particle diameter is 1 micrometer or less are also given by the particle size distribution. To some extent included. Moreover, among the granular inorganic compounds, there are those that are crushed during melt-kneading to reduce the particle size. For this reason, even if a granular inorganic compound having an average particle diameter of 1 to 100 μm is used, pores having a diameter of 0.1 to 100 μm are formed in the obtained carrier, including a smaller range. become.

  The granular biological treatment carrier of the present invention is preferably spherical or elliptical. As the size, the average particle size is preferably 3 to 15 mm, more preferably 4 to 13 mm. The most common method for forming into a spherical shape is hot-cut when extruded from a kneader. In addition, a method of pelletizing after passing through a normal water bath and dropping corners with a mill or the like may be used, or a molding method such as injection molding may be used. The smaller the average particle size of the carrier, the larger the surface area per unit volume of the plurality of carriers and the higher the treatment efficiency. However, when the average particle size is 3 mm or less, the screen for separating the treated water and the carrier The mesh width becomes smaller and the water flow resistance becomes larger, which tends to hinder water treatment. On the other hand, when the average particle diameter is larger than 15 mm, the surface area per unit volume by a plurality of carriers tends to be small, and the processing efficiency tends to decrease.

Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited only to the following examples.
Evaluation methods in the following examples and comparative examples are as follows.

(1) Melt flow rate (MFR);
According to JIS K7210, measurement was performed at a temperature of 190 ° C. and a load of 21.2 N (2.16 kg) from the conditions in Table A. The unit of MFR is g / 10 minutes.

(2) Microstructure observation and pore size measurement The produced carrier was immersed in liquid nitrogen and divided, and the fracture surface was observed with a scanning electron microscope (SEM). The size of the hole observed at this time was measured and expressed in the range of the thinnest and the thickest.

(3) Apparent density Measured using A & D Corporation Balance: HA-202M Specific gravity measurement kit: AD-1653.

(4) BOD average removal rate (%)
20 liters of carrier is put into a 100 liter treated water tank (filling rate 20%), and as raw water, noodle wastewater with a BOD of 560 mg / liter is aerated from the bottom of the tank with an air amount of 8 liters / minute while stirring, Processed at 20 liters / hour. Treated water was collected when 20 days, 25 days, and 30 days had elapsed after the start of operation, and BOD was measured to determine the average removal rate of BOD from raw water.

(5) Durability After the above treatment (4) is continued for 3 months, the carrier is taken out and the size before the treatment is examined (average values of major and minor diameters of particles are measured for 50 carriers). Then, an average value was obtained for them), and the percentage of the initial value was examined. The smaller the value, the better the durability.

[material]
Next, various raw materials used in the following Examples and Comparative Examples are shown.
(1) Resin Resin A: Polyethylene (manufactured by Nippon Polyethylene YF30, MFR = 1.1 g / 10 min)
Resin B: Polyethylene (manufactured by Nippon Polyethylene LF547, MFR = 3.8 g / 10 min)
Resin C: Polypropylene (K5019F manufactured by Chisso Corporation, MFR = 5.4 g / 10 min)
Resin D: Inorganic filled nylon 6 (Unitika A3130, MFR = 20 g / 10 min)

(2) Inorganic compound N: sodium chloride (manufactured by Ako Kasei Co., Ltd., Osiomicron T-0, average particle size 10 μm)
M: Magnesium sulfate (manufactured by Ako Kasei Co., Ltd. MG-0K, average particle size 70 μm)
O: Magnesium sulfate (manufactured by Ako Kasei Co., Ltd. MG-0K-100, average particle size 10 μm)

Example 1
100 parts by mass of resin A and 100 parts by mass of inorganic compound N were extruded from a die (diameter 5 mm × 2 holes) using a twin screw extruder (Ikegai Co., Ltd., PCM-30). A spherical sample having a diameter of about 5 mm was prepared by hot cutting at an extrusion temperature of 190 ° C. and a screw rotation speed of 150 rpm. The inorganic compound N was extracted from the sample by treating this in hot water for 8 hours. The result of observing the cross section of the carrier thus obtained with SEM is shown in FIG. As shown in the figure, a large number of minute holes were formed. Table 1 shows the apparent density and pore size of the carrier.

  Using this carrier, the average removal rate of BOD after treating the noodle making waste water was determined. The results are shown in Table 1. The initial particle size and the change in particle size after 3 months were also determined. The results are also shown in Table 1.

Examples 2-12, Comparative Examples 1-3
The type of resin, the type of inorganic compound, and the quantitative ratio thereof were changed as shown in Table 1 to prepare a carrier. And then. Otherwise, the test was conducted in the same manner as in Example 1. However, in Example 9, as compared with Example 1, the extrusion temperature was changed to 210 ° C. and the screw rotation speed was changed to 250 rpm. Moreover, in Example 10, compared with Example 1, the extrusion temperature was changed to 210 degreeC. In Example 11, the initial particle size was changed to be larger than those in other Examples 1 to 10, and in Example 12, the initial particle size was changed to be smaller. The results are shown in Table 1.

  In Example 1, the apparent density and pore size were within the scope of the present invention, so that the BOD average removal rate was high and the carrier was excellent in durability. Similarly, in Examples 2 to 12, even when the kind of resin, the kind of inorganic compound, and the quantity ratio at the time of production were changed, the apparent density and the size of the pore were within the scope of the present invention. It was a carrier having a high rate and excellent durability. However, since the initial particle diameter of the carrier of Example 11 was large, the BOD removal rate was slightly lower than that of Examples 1-10. Moreover, since the initial particle diameter of the carrier of Example 12 was small, the BOD removal rate was similarly slightly lower than that of Examples 1-10.

  In Comparative Example 1, no inorganic compound was used, so no pores were formed. Therefore, the durability was good, but the average BOD removal rate was poor. In Comparative Example 2, as a result of too much compounding amount of the inorganic compound, the pores become large and some of the results are outside the scope of the present invention. Even though BOD removal can be performed to some extent, the durability deteriorates. Oops. In Comparative Example 3, the amount of the inorganic compound was very large, resulting in a low apparent density and a very large pore size, which was significantly out of the scope of the present invention. It was. For this reason, the carrier floated in the aeration tank, so that efficient water purification treatment was impossible, the BOD average removal rate was poor, and the durability was also poor.

It is a figure which shows the result of having observed the cross section of the support | carrier of Example 1 of this invention by SEM.

Claims (2)

  A biological treatment carrier characterized in that it is composed of granules made of a thermoplastic resin having pores having a diameter of 0.1 to 100 µm, and has an apparent density of 0.5 to 1.5 g / ml.   A thermoplastic resin and a granular inorganic compound are melt-kneaded to form a granular body, and then the granular body is treated with a solvent that dissolves the inorganic compound but does not dissolve the thermoplastic resin. By removing the inorganic compound from the body, pores having a diameter of 0.1 to 100 μm are formed in the portion where the inorganic compound was present, and the apparent density of the granular material is 0.5 to 1.5 g / ml. A method for producing a carrier for biological treatment, characterized in that

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