JP2000061487A - Carrier for microorganism and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of biological treatment in an aeration tank by constituting a carrier for microorganisms of a porous polystyrene body. SOLUTION: A carrier for microorganisms arranged in an aeration tank is made essentially of polystyrene, preferably polystyrene obtd. by recovering foamed polystyrene products, pelletizing and making porous, thereby the carrier has an excellent function and can be obtained at a moderate price. Furthermore, as a method of making polystyrene porous, water-soluble crystalline compounds are incorporated into polystyrene melt to disperse them and formed articles obtained from the mixture are immersed in water to dissolve the crystals, and then a porous polystyrene body can be easily obtained. The carrier for microorganisms excellent in property with which the efficiency of biological treatment in the aeration tank can be improved can be produced at a moderate price. As a result, without changing a conventional active sludge treating device, treatment of organic waste water can be economically realized.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carrier for microorganisms used in treating organic wastewater with activated sludge and a method for producing the same.

[0002]

2. Description of the Related Art Pollutants in water are decomposed and purified in nature such as rivers and lakes by being subjected to physicochemical and biological actions such as precipitation, aggregation, oxidation and reduction. In particular, contaminants containing organic substances are easily purified by microorganisms by a biological action. As a method for purifying organic wastewater using this, there is an activated sludge method of treating organic wastewater with activated sludge containing aerobic microorganisms, but the method has a high purification capacity and relatively low treatment cost. Therefore, it is widely used in sewage treatment, industrial wastewater treatment, etc.

In the above-mentioned activated sludge method, waste water p
After pretreatment such as H adjustment and homogenization, the organic wastewater is led to an aeration tank (aeration tank), and in this aeration tank, BOD is shown by activated sludge containing aerobic microorganisms while blowing oxygen. Purification is performed by decomposing organic pollutants in wastewater. Therefore, in order to realize efficient biological treatment in the aeration tank, it is preferable to use an aeration tank that has a large contact area with the organic wastewater air. The organic wastewater treatment facility by the law requires a relatively large site and tends to be large.

On the other hand, in order to make the treatment equipment compact, a carrier for microorganisms for supporting microorganisms is arranged in the aeration tank to improve the treatment efficiency by creating an environment in which the microorganisms can comfortably live. , High-concentration and high-load organic wastewater treatment is performed. As the carrier for microorganisms used at this time, for example, those prepared by insolubilizing polyvinyl alcohol, and molded products made of polyethylene glycol, polyurethane, high density polyethylene, or the like are known.

However, a good carrier for microorganisms is
It has a high affinity with microorganisms, is not toxic, has excellent fluidity in water, and causes deterioration due to microorganisms and enzymes,
Since various performances such as no abrasion due to aeration treatment are required, it is necessary to be specially prepared as a carrier for microorganisms, and there is a problem that the unit price becomes high. That is, since the aeration tank used in the activated sludge method occupies a large volume, a large number of microbial carriers are required in order to improve the treatment efficiency, and if the unit price of the carrier is high, the treatment cost will increase.

On the other hand, as a completely different problem, since the distribution mechanism in recent years is widespread, light and durable Styrofoam is widely used as a packaging material for food trays, packaging containers, or packaging cushioning materials. And
The problem of disposal is becoming more serious. Further, since Styrofoam is made from petroleum, which is a finite earth resource, as a raw material, effective utilization of resources is required.

For this reason, a part of Styrofoam products such as food trays is being collected through a distribution organization, and is being recycled and reused. At this time, since the collected Styrofoam is very bulky, transporting it to the recycling factory as it is will increase the transportation cost, so at an early stage, the Styrofoam product collected is melted and pelletized. Has been. However, the regenerated polystyrene pellets obtained as described above cannot be used depending on the application because of the problem of impurities, and even if it can be used, it is used in a state mixed with a small amount of virgin material. The current situation. In this way, for used Styrofoam products, although the collection system is considerably enhanced and consumers are more conscious of collection, effective use of regenerated polystyrene pellets has not been achieved and a large amount At present, we are looking for applications to be used.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a carrier for microorganisms having excellent characteristics, which can effectively improve the efficiency of biological treatment in an aeration tank, at low cost. Still another object of the present invention is to make effective use of regenerated polystyrene pellets and achieve environmental protection on a global scale.

[0009]

The above objects can be achieved by the present invention described below. That is, the present invention is a carrier for microorganisms comprising a porous polystyrene body and a method for producing the carrier for microorganisms.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to preferred embodiments of the present invention. As a result of intensive research to solve the above-mentioned problems of the prior art, the inventors of the present invention arranged in an aeration tank for the purpose of efficiently treating organic wastewater with activated sludge containing aerobic microorganisms. Microorganism carrier, polystyrene as the main raw material, preferably using a polystyrene raw material obtained by collecting and pelletizing expanded polystyrene products, if the polystyrene is made porous, it has an excellent function, yet an inexpensive microbial carrier The present invention has been accomplished by finding that it can be obtained.

Further, as a method for making polystyrene porous, a water-soluble crystalline compound is mixed and dispersed in a polystyrene melt, and a molded article obtained from the mixture is immersed in water to dissolve the above crystals. It was found that a porous polystyrene body can be easily obtained by doing so. Furthermore, if a high density inorganic filler is added to the polystyrene melt,
It was also found that its specific gravity can be easily adjusted to a range suitable as a carrier for microorganisms.

The carrier for microorganisms of the present invention and the method for producing the same will be described below in more detail. As described above, the carrier for microorganisms of the present invention is made of porous polystyrene, and in particular, from the viewpoint of economical efficiency and environmental problems, it may be composed mainly of polystyrene recovered from discarded expanded polystyrene. preferable. That is, Styrofoam used in food trays, packaging containers or cushion materials is usually recovered, then melted in a hot air oven at about 350 ° C. and pelletized, and is marketed at a relatively low cost as a recycled material. Therefore, in the present invention, it is preferable to use the regenerated polystyrene pellets as the raw material of the carrier for microorganisms.

The preferred method for producing the carrier for microorganisms of the present invention will be described below. As described above, the carrier for microorganisms of the present invention comprises a porous polystyrene body,
From the viewpoint of economy and protection of the global environment, it is preferable to use regenerated polystyrene pellets recovered from expanded polystyrene as the main raw material, but a porous body can be easily obtained from the regenerated polystyrene pellets by the following method. First, the regenerated polystyrene pellets are melted, a water-soluble crystalline compound is mixed and dispersed in the melt, and the obtained mixture is extrusion-molded at a temperature of about 200 to 250 ° C. by an extruder. A molded product is obtained by cutting into a desired size. Next, the obtained molded product is immersed in water to dissolve the water-soluble crystalline compound dispersed in the molded product. As a result, the surface of the molded product, and further the crystalline compound present inside the molded product, is dissolved in water, so that pores are formed in the dissolved part and a porous molded product is obtained. If the porous polystyrene body formed in this way is introduced into the aeration tank as a carrier for microorganisms, it becomes possible to inhabit more microorganisms, the concentration of microorganisms in the aeration tank is increased, and the treatment efficiency is improved. To be achieved.

The water-soluble crystalline compound used above is a compound which is well dispersed in a molded article and dissolves well in water when the molded article is immersed in a water tank. Furthermore, it is preferable to use a substance that does not adversely affect microorganisms or treated water in consideration of the fact that it remains inside the carrier. Specific examples include hydrogen carbonate, carbonate, hydrogen sulfate, and salt. For example, potassium hydrogen carbonate,
It is preferable to use water-soluble crystalline compounds such as sodium carbonate, sodium hydrogencarbonate, potassium hydrogensulfate, sodium hydrogensulfate and sodium chloride.

Further, the microbial carrier of the present invention, when stored in an aeration tank, is arranged at a suitable position in the organic wastewater without floating on the surface of the organic wastewater. It is preferable that its specific gravity is adjusted to an appropriate range. For example, in order to further improve the fluidity in water in the range of 0.80 or more and 1.20 or less, the specific gravity should be adjusted in the range of 1.00 to 1.10. preferable. The specific gravity of polystyrene, which is the main component of the carrier for microorganisms of the present invention, is usually 1.04 to 1.1.
It is considered that the specific gravity is lighter than that of the porous body because it is a porous body. Therefore, in the present invention, it is preferable to adjust the specific gravity of the carrier for microorganisms to a suitable range.

As a method for adjusting the specific gravity of the carrier for microorganisms of the present invention comprising a porous polystyrene body, in the above-mentioned method for producing a porous polystyrene body, a high density inorganic filler is added to the polystyrene melt. A method of adding it to the carrier for microorganisms may be mentioned. The inorganic filler that can be used in this case has a high density, and when it is contained in a porous polystyrene body, a molded body having a desired specific gravity can be obtained, and it is non-toxic, and when it is added, it becomes porous. Any of them can be used as long as the durability and physical properties of the high quality polystyrene body are not impaired. Specific examples include zeolite, metallic iron, various iron-containing alloys, calcium carbonate, barium sulfate, and the like. Of these, zeolite is an inorganic porous material, and as such is effective as a microorganism carrier, it can be particularly preferably used in the present invention.

According to the studies by the present inventors, in particular, zeolite is used as the inorganic filler, and hydrogencarbonate or carbonate crystals are used as the water-soluble crystalline compound to prepare the carrier for microorganisms of the present invention. If so, all of these materials are inexpensive, do not adversely affect microorganisms and treated water, and since the crystals are easily dissolved in water, a carrier for microorganisms having excellent functionality can be easily obtained. . In addition, in the case of producing the carrier for microorganisms of the present invention, it is needless to say that other additives may be mixed for the purpose of improving the strength and durability thereof.

[0018]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention. Example 1 An activated sludge treatment of organic wastewater was carried out using a 500 liter / day scale pilot plant constructed according to a normal activated sludge treatment flow. The properties of the raw water used for the treatment are shown in Table 1 below, and as the raw water, organic wastewater from a food factory was used.

Table 1 Raw water condition (waste water of food factory)

First, with respect to the above raw water, pH 7.0,
The activated sludge treatment was performed under the operating conditions of a BOD load of 1.0 kg / m ³ and an HRT of 2.0 days. At that time, the carrier for microorganisms of the present invention was introduced at a ratio of 20% in apparent volume, and activated sludge treatment was carried out while aerated and flowing. The carrier for microorganisms used in this example was prepared as follows. First, melt the recycled pellets of Styrofoam,
Crystals of potassium hydrogen carbonate and zeolite were mixed and dispersed therein, and the mixture was extruded into a cylinder having a diameter of 20 mm by an extruder to obtain a cylindrical molded body cut into a length of 30 mm. Next, the obtained molded body was immersed in a sufficient amount of water to dissolve potassium hydrogen carbonate. The average specific gravity of the obtained porous body was measured and found to be 1.10. In this example, the microbial carrier was added to the activated sludge.
What was soaked for a day was used.

Comparative Example 1 An activated sludge treatment test was conducted in the same manner as in Example 1 except that the carrier for microorganisms of the present invention was not added.

[0022]

[Evaluation] After the aeration treatment, the sludge concentration in the activated sludge in the aeration tank in Example 1 and Comparative Example 1 was measured, and in Example 1, it was 8,000 mg / l, whereas in Comparative Example 1, , 4,000 mg / l. As a result, in the case of Example 1 using the carrier for microorganisms of the present invention, it was confirmed that the concentration of microorganisms in the aeration tank was high. Furthermore, when the BOD of the treated water after the treatment performed in Example 1 and Comparative Example 1 was measured, the BOD value could be reduced as compared with the case of Comparative Example 1, and efficient activated sludge treatment was performed. I was able to confirm that it was done.

[0023]

As described above, according to the present invention, a carrier for microorganisms having excellent characteristics capable of achieving an improvement in the efficiency of biological treatment in an aeration tank is provided at low cost. As a result, without changing the conventional activated sludge treatment device,
Economical treatment of organic wastewater is realized. Further, according to the present invention, the recycled styrofoam pellets can be effectively utilized, and environmental protection on a global scale can be achieved.

Claims (4)

[Claims] 1. A carrier for microorganisms comprising a porous polystyrene body. 2. The carrier for microorganisms according to claim 1, which is composed mainly of polystyrene recovered from the discarded expanded polystyrene. 3. A water-soluble crystalline compound is mixed and dispersed in a polystyrene melt obtained by melting discarded Styrofoam, and a molded article obtained from the mixture is immersed in water to form the above crystal. A method for producing a carrier for microorganisms, which comprises dissolving a hydrophilic compound to obtain a porous polystyrene body. 4. The method for producing a carrier for microorganisms according to claim 3, further comprising adding an inorganic filler to the polystyrene melt to adjust the specific gravity of the porous polystyrene body.