JPH0374156B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention immobilizes microbial cells on a carrier in a membrane shape,
The present invention relates to a microbial cell-immobilized carrier used in the biochemical treatment of wastewater in which wastewater containing organic matter is treated by bringing it into contact with the immobilized biofilm, and a method for producing the carrier.

[Prior art] In order to remove organic matter dissolved in wastewater,
Biochemical treatment using microorganisms is used. Conventionally, this method was generally an activated sludge method in which aerobic microorganisms, which grow using organic matter in wastewater as a substrate, are suspended in a treatment equipment and aerated, but this method has a low density of microorganisms in the treatment equipment, so There were problems such as the small amount of wastewater treated per volume, the difficulty in maintenance, and the difficulty in solid-liquid separation depending on the state of floc formation. To overcome this drawback, anthracite, sand, activated carbon, etc. are used as microbial carriers, and organic matter is treated by attaching biofilm using either a fixed bed type in which the microbial carrier is filled into the processing equipment, or a fluidized bed type in which it is fluidized as a granular material. The biofilm method is used.

[Problems to be Solved by the Invention] In the treatment method using the above microorganism-immobilized carrier, the density of microorganisms in the treatment device becomes high, so the amount of wastewater treated per unit volume increases. Furthermore, since a carrier is used, solid-liquid separation is easy and the amount of surplus sludge generated is small. However, it is difficult for biofilms to adhere to these carriers for a long time after the start of operation, and even if they do, once the biofilm detaches due to collisions between carriers, it takes a long time for it to attach again, and microorganisms The problem was that the quality of the treated water deteriorated significantly until it covered the surface of the carrier again.

For this reason, entrapping immobilization methods have been developed in which the bacterial cells are encapsulated in a fine lattice of gel or coated with a semipermeable polymer film. Many materials are used, such as acrylamide and agar. However, when immobilizing aerobic microorganisms and using them for biological treatment of wastewater, in the inclusion method, the diffusion of oxygen into the gel becomes rate-limiting, limiting the growth of microorganisms, and depending on the type and size of the carrier, it is effectively Only microorganisms on the surface layer participate in the reaction. In addition, in the entrapment immobilization method, in principle, the bacterial cells themselves are not directly involved in reactions such as binding, but in actual immobilization operations, monomers and polymers that are the raw materials for the polymer gel and film that envelop the bacterial cells are used. Since the bacteria are immobilized by mixing the bacteria and the bacteria and proceeding with a reaction such as polymerization or insolubilization, the bacteria may become inactivated during this process. On the other hand, if bacterial cells can be bonded and immobilized on the surface of a polyvinyl alcohol carrier under mild conditions, deactivation during immobilization can be prevented, and the bacterial cells can easily devitrify the substrate and oxygen on the surface of the carrier. Therefore, it can be advantageously used as a carrier.

The method of using polyvinyl alcohol as a bacterial cell immobilization carrier in the entrapment method is the freezing method (patent application 1983-
261547) and the boric acid method (Japanese Patent Application No. 1983-222832). However, in the freezing method, it is necessary to put it into a mold and gel it by freezing, and then mold it into a cylinder, rectangular parallelepiped, etc., and in such shapes, the corners are worn and rounded due to mechanical stirring and ventilation, resulting in loss of carrier. There was a drawback. Furthermore, both the freezing method and the boric acid method have the disadvantage that when used in water, the gel dissolves and the immobilized bacterial cells leak out, making it impossible to use them for a long time in a wastewater treatment device.

In addition, the conventional immobilization method of microorganisms using anthracite, sand, etc. is carried out by filling a column with a carrier and continuously passing water through the desired microorganism suspension.
It was something that had bacterial bodies that naturally attached to it, but
This method has the problem that the amount of bacterial cells cannot be controlled, and the attached biofilm is extremely thin, making it impossible to maintain a high density of bacterial cells per surface area of the carrier.

Therefore, in order to eliminate the drawbacks of the prior art, the present invention immobilizes microorganisms on the surface of a carrier, so that they act as propagating bacteria, which makes it easy for biofilm to adhere at the start of operation, and even when the biofilm peels off. The object of the present invention is to provide a microbial cell immobilization carrier that can be rapidly regenerated.

[Means for Solving the Problems] In order to achieve the above object, the first aspect of the present invention is to dissolve gel beads made of hydrophilic plastic such as polyvinyl alcohol, and to attach microbial cells attached to the swollen surface of the plastic. This is a carrier for immobilizing microorganisms for wastewater treatment by bonding and immobilizing them in a state where they are partially encapsulated by the regelled product.The second invention uses gel beads made of hydrophilic plastic as the carrier, and the microorganisms are specially coated on the surface of the gel beads. It is characterized by being immobilized in a fixed manner. That is, after dropping an aqueous solution of a hydrophilic plastic such as polyvinyl into a gelling agent solution and gelling it, the resulting gel beads are poured into water, or an aqueous solution of a substrate of microorganisms to be immobilized, or the cells are centrifuged. The microbial cells were dissolved and swollen in the supernatant, and then the lyophilized microbial cells were adhered to the swollen gel beads, and the microbial cells were repeatedly frozen and thawed to re-gel. The present invention relates to a method for producing a bacterial cell-immobilized carrier for wastewater treatment, which is characterized by binding and solidifying the carrier in a semi-enclosed form with a compound.

In the present invention, hydrophilic plastics are defined as those that swell in water to become pasty, that the swelling operation has no adverse effect on the immobilized microorganisms (for example, swelling in organic solvents is inappropriate), and that it is not suitable for freezing. , The bacteria should not be allowed to react in a solution after being made sticky (as in thawing) (adhesive bacteria will fall off in a solution), and furthermore, it should not re-gel during freezing and thawing. Desirably, polyvinyl alcohol is commonly used.

Polyvinyl alcohol is broadly classified into completely saponified products and partially saponified products depending on the degree of saponification, and further classified into low degree of polymerization (300-500), medium degree of polymerization (1000-1500), and high degree of polymerization (1700). ~2400). Among these, it is considered desirable to use a completely saponified product with a medium degree of polymerization in view of its solubility in water, aqueous solution viscosity, and its stability, but the present invention is not limited to this, and the microorganisms to be immobilized are Various polyvinyl alcohols can be used depending on the body. The higher the concentration of polyvinyl alcohol, the higher the gel strength of the resulting carrier gel, but it was dissolved in water to a concentration of 10 to 14% based on its solubility in water and the viscosity of the aqueous solution. Also, heating is required for melting, but this heating method is similar to the method of blowing steam (85
~95℃), but an autoclave (pressure cooker) (100~120℃) was used to prevent the formation of mako.
The polyvinyl alcohol aqueous solution dissolved in this manner is immediately dropped into the gelling agent from a syringe having a narrow opening to form droplets to obtain a spherical gel. Examples of gelling agents include sodium chloride, sodium sulfate, borax, boric acid, methyl alcohol,
Although acetone or the like can be used, a saturated boric acid aqueous solution was used because of its gelling property. In order to allow gelation to proceed completely, the material is stirred and suspended in the gelling agent for about one night, then taken out and thoroughly washed with running water to remove the gelling agent from the surface.

As mentioned above, conventional methods for immobilizing microorganisms cannot control the amount of microbial cells, and the attached biofilm is extremely thin, making it impossible to maintain a high density of microbial cells per surface area of the carrier. In contrast, in the present invention, free water, interstitial water, etc. contained in the bacterial cells are sublimated and removed by freeze-drying the bacterial cells to be immobilized, and the dry bacterial weight per unit volume is increased. Because it is immobilized, bacterial cell density can be maintained at a high level.

That is, by mixing the gel beads washed with water as described above in water or the supernatant obtained by centrifuging the bacterial cell suspension and stirring for several hours, the surface of the beads swells, dissolves, and becomes pasty. Separate this from water,
Mix with separately freeze-dried cells, stick the dried cells to the surface, freeze in the freezer (-20 to -80℃), thaw at room temperature, and repeat this freezing process 2 to 3 times. The surface of the gel that has been dissolved by heating is re-gelled. The dried bacterial cells that had been adhering to the resurfaced gel were bound and immobilized in a manner that they were partially encapsulated in the gel. Therefore, as a side effect, the present invention can also be used to immobilize anaerobic bacteria, which are said to have a lower adhesion to carriers than aerobic bacteria, and we believe that its use in wastewater treatment will expand. It will be done.

In addition, the above-mentioned Japanese Patent Application Nos. 59-261547 and 59-261547
When the bacteria are immobilized by the freezing method or the boric acid method as in No. 222832, there is a risk that the gel will dissolve during the treatment period and the immobilized bacteria may leak out. On the other hand, when the bacteria are immobilized on the surface after making a spherical gel with polyvinyl alcohol as in the present invention, the problem of molding can be easily avoided, and when using the immobilization carrier, The growth of the cells bound to the surface causes the cells to adhere to each other and maintain the gel shape, making it possible to provide an immobilization carrier that can withstand long-term use.

FIG. 1 shows a flow sheet for preparing the immobilization carrier of the present invention, in which reference numeral 1 indicates dissolution of PVA, reference numeral 2 indicates an aqueous solution of PVA, and reference numeral 3 indicates dissolution of PVA by dropping an aqueous PVA solution into a gelling agent solution to form a gel. 4 is separation and washing of gel beads, 5 is surface redissolution of gel beads, 6 is suspension of immobilized microorganisms, 7 is centrifugation, 8 is freeze drying, 9 is pulverization, 10 is surface redissolution of gel beads and Mixing with crushed dry bacterial cells, 11 frozen, 1
2 indicates thawing, 13 a circuit for repeating freezing and thawing, and 14 an immobilization carrier.

As described above, according to the present invention, the bacterial cells immobilized on the surface of the carrier act as proliferating bacteria, and the biofilm quickly attaches to it, and even if the biofilm peels off during operation, it is quickly regenerated. This process consistently results in treated water of good quality.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

[Example] 250 g of polyvinyl alcohol with a saponification degree of 98% or more and a polymerization of about 2000 was suspended in 2 parts of water, and dissolved by heating at 120°C (2 kg/cm ² ) for 20 minutes using an autoclave. This aqueous solution was dropped into a saturated boric acid aqueous solution through a 1 mm diameter nozzle to produce spherical vinyl alcohol gel beads, which were stirred overnight in the boric acid solution. Purification microorganisms (activated sludge) (MLSS4100mg/
) 5 was collected by centrifugation, the bacterial cells were dispersed and suspended in 200 ml of 3% sucrose solution, freeze-dried at -55°C for 2 hours, and then ground with a dry grinder to obtain 21 g of dry powdered bacterial cells. I got it. The activated sludge was centrifuged and stirred for 5 hours in the supernatant, and polyvinyl alcohol gel beads whose surfaces had been dissolved were mixed with dried bacterial cells to adhere the bacterial cells to the surface. This is −40℃
After freezing in a freezer for one day, thawing was performed at room temperature, and this freezing and thawing operation was repeated twice to regelify the dissolved gel to obtain 2180 g of immobilized carrier.

The obtained immobilization carrier has a spherical shape with a diameter of 3.5 to 4 mm and is covered with a thin film of polyvinyl alcohol in which a portion of the dried bacterial cells that have adhered to the surface of the gel beads has been regelled.

Test Example The immobilized carrier obtained in Example 1 was put into a 3-volume aeration tank, and urban sewage (COD _Mo : 120-170 mg/, SS: 150-200 mg/
) was treated by continuously passing water through it for a residence time of 4 hours and a volumetric load of 2.0 Kg-BOD/m ³ ·day. Figure 2 shows the results after 90 days of operation. The treated water became stable on the third day, and good treated water was stably obtained thereafter.

[Brief explanation of drawings]

FIG. 1 is a process diagram for producing the microorganism-immobilized carrier of the present invention, and FIG. 2 is a diagram showing the daily change in BOD when wastewater is aerated using the same carrier.

Claims (1)

[Scope of Claims] 1. A wastewater treatment characterized in that microbial cells adhered to the solubilized and swollen surface of hydrophilic plastic gel beads are bound and immobilized in a state in which they are partially encapsulated by the regelled product of the plastic. Microorganism immobilization carrier. 2. After gelling an aqueous solution of hydrophilic plastic in a gelling agent solution, the resulting gel beads are placed in water, an aqueous substrate solution of microbial cells to be immobilized, or a supernatant obtained by centrifuging the microbial cells. After being solubilized and swollen, the frozen and dried microbial cells are adhered to the swollen gel beads, and then frozen and thawed are repeated to regelify the microbial cells, and the microbial cells adhered to the surface of the gel beads are partially encapsulated by the regelled product. A method for producing a microorganism-immobilized carrier for wastewater treatment, characterized by binding and immobilizing microorganisms in such a form.