JPH09252771A - Biological carrier and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a biological carrier predicable without using precipitation separation process or screen separation process having various problems and to provide a process for the production of the biological carrier. SOLUTION: This biological carrier is composed of a hydrated gel of a polyvinyl alcohol containing 20-50vol.% of dispersed polymethylpentene particles and 5-13vol.% of dispersed foamed polystyrene particles and has a specific gravity of 0.92-0.99 and a particle diameter of 2-10mm. The carrier can be produced by adding dispersible particles of the above resins to an aqueous solution of a polyvinyl alcohol, mixing the composition, repeating the freezing and thawing of the mixture to obtain a gel having the above specific gravity and granulating the gel to the above particle diameter.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carrier for immobilizing useful microorganisms such as nitrifying bacteria and denitrifying bacteria used for treating wastewater such as sewage, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a biological carrier for immobilizing nitrifying bacteria or denitrifying bacteria, a gelled product of polyvinyl alcohol has been known, and a freezing method and a boric acid method are generally used as the production method. In these methods, after polyvinyl alcohol is heated and dissolved in water, seed sludge containing a large amount of cells to be immobilized is mixed. In the freezing method, freezing and thawing are repeated, and in the boric acid method, in a saturated boric acid solution. A biological carrier can be obtained by gelling and granulating by, for example, dropping into.

The behavior of the thus obtained carrier in the treatment of waste water will be described with reference to FIG.
Is mixed with the activated sludge mixed solution in the latter half of the aerobic tank 12 of the reaction tank 1 including the anaerobic tank 11 and the aerobic tank 12, and is circulated up and down together with the mixed solution by aeration by the air diffuser 14. Flows and promotes oxidative action. In this case, the carrier 10 has a specific gravity of 1.26 to 1.28.
Since it is formed of a gelled product having a specific gravity of 1.02 to 1.03, which is slightly larger than that of water, which is made from the polyvinyl alcohol as a raw material, it coexists well with the mixed solution.

Next, at the end of the aerobic tank 12, the carrier 10 and the activated sludge mixed solution are separated, and the separated mixed solution is transferred to the next settling tank. As an operation for separating the carrier 10 and the activated sludge mixed solution, there are a screen separation method using a wedge wire screen 13 shown in FIG. 8 and a precipitation separation method using a difference in specific gravity between the activated sludge mixed solution.

In the case of a screen separation method using a screen, the discharge of solid impurities flowing in together with the stock solution is hindered by the screen, so that the impurities are successively concentrated and accumulated in the aerobic tank to make the purification treatment unstable. However, there is a problem that the screen is clogged by the flocculent microorganisms generated in the tank, and it takes a lot of labor and cost for maintenance to remove them.

Further, in the case of the precipitation separation method utilizing the difference in specific gravity from the activated sludge mixed liquid, the specific gravity of the carrier 10 is 1.02 to 1.02.
Since 1.03 is close to the specific gravity of the activated sludge, it is difficult to reliably separate it from the activated sludge, and the carrier 10 flows out from the reaction tank 1 to the next settling tank along with the sludge. was there.

[0007]

The present invention provides a biological carrier and a method for producing the same, which does not require the use of the precipitation separation method or the screen separation method which have various problems as described above. In particular, the present invention provides a biological carrier suitable for the floating separation method and a method for producing the same. Here, the outline of the flotation separation method will be described. FIG. 9 shows a cross section of the main part of the flotation separation tank. , The upper flow section 15 to the lower flow section 16
During the flow of the sludge, the carrier having a smaller specific gravity than the activated sludge mixed liquid floats by buoyancy and collects upward.
On the other hand, the activated sludge mixed liquid from which the carrier has been separated in this way is taken out from the upper outlet of the second upper fluidizing section 17. As described above, the flotation method is performed by making the specific gravity of the carrier smaller than 1, which is the specific gravity of the activated sludge mixed solution.
This is a method that uses buoyancy.

[0008]

The above problems can be solved by the following biological carriers. (1) A biological carrier comprising granules of a hydrated gelled product of polyvinyl alcohol containing dispersed particles of a synthetic resin and having a specific gravity of less than 1.0. (2) A biological carrier comprising a core particle of a synthetic resin coated with a hydrated gel of polyvinyl alcohol and having a specific gravity of less than 1.0.

The above-mentioned solving means can be embodied as follows. In the biological carrier according to (1) above,
The dispersed particles are particles of polymethylpentene or foamed resin, and the specific gravity of the hydrated gel particles is 0.92 to 0.99.
A biological carrier that is within the scope of. In the biological carrier according to (2), the core particle is a particle of expanded polypropylene, expanded polyethylene, polymethylpentene or expanded nylon, and has a specific gravity within the range of 0.92 to 0.99. .

The above problems can be solved by the following method for producing a biological carrier. (3) A method for producing a biological carrier, characterized in that dispersed particles of a synthetic resin are added to an aqueous solution of polyvinyl alcohol, mixed, and then frozen and thawed repeatedly to form a gelled product having a specific gravity of less than 1.0. (4) An organism characterized by forming a film of an aqueous solution of polyvinyl alcohol on the surface of core particles of a synthetic resin, and bringing the film into gel by contacting with an aqueous solution of boric acid so that the specific gravity is less than 1.0. Method for producing carrier.

The above solving means can be embodied as follows. The method for producing a biological carrier according to (3) above, wherein the dispersed particles are particles of polymethylpentene or expanded resin, and a gelled product having a specific gravity within the range of 0.92 to 0.99 is formed. In the method for producing a biological carrier according to (4), the core particles are particles of expanded polypropylene, expanded polyethylene, polymethylpentene or expanded nylon, and the specific gravity after gelation is within the range of 0.92 to 0.99. How to be. In the method for producing a biological carrier according to any one of the above, a method in which activated sludge is added to and mixed with an aqueous solution of polyvinyl alcohol.

[0012]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described with reference to FIGS. First, the first embodiment of the biological carrier of the present invention is a synthetic resin dispersed particle 2 as shown in FIG.
It is composed of granules of hydrated gelled product 2 of polyvinyl alcohol containing 1 and has a specific gravity of less than 1.0 as a whole.
This biological carrier disperses, as dispersed particles, 20 to 50% by volume of particles of polymethylpentene having a specific gravity of about 0.8, or 5 to particles of expanded resin such as expanded polystyrene having a specific gravity of about 0.25. It is contained by being dispersed by 15% by volume, and the specific gravity of the whole hydrated gel material is 0.9.
It can be embodied by setting the size within a range of 2 to 0.99 as a spherical diameter or a length of one side of a hexahedron of about 2 to 10 mm.

The second embodiment of the biological carrier of the present invention comprises a core granule 31 of a synthetic resin coated with a hydrated gelation product 3 of polyvinyl alcohol as shown in FIG. 1 (B). The total specific gravity is less than 1.0. Further, in this biological carrier, the core particles are particles of expanded polypropylene, expanded polyethylene having a specific gravity of about 0.25, polymethylpentene or expanded nylon having a specific gravity of about 0.8, and 0.5 to 1 mm. It is covered with the hydrated gelation product 3 having a certain thickness, and the total specific gravity is within the range of 0.92 to 0.99, and the size thereof is the same as the diameter or the length of one side. 2-10m
It can be embodied by setting it to about m. In any of the above embodiments, in order to impart a useful microorganism such as a nitrifying bacterium or a denitrifying bacterium to a carrier, the microorganism is entrapped in advance in the hydrated gelled product, or bound after gelation. The same microorganism may be inoculated by the method.

Since the biological carrier of the present invention is constructed as described above, it can be preferably applied to the flotation separation method while having the same nitrifying or denitrifying function as the conventional carrier.
If the specific gravity or particle size of the carrier is selected within the above range, the flow uniformity in the reaction tank is maintained, and a preferable biological reaction can be expected without uneven distribution of the carrier. Further, since an appropriate floating speed can be set in the floating separation tank, the separation property is high and it is possible to properly prevent the residual liquid from flowing out of the mixed liquid after separation.

Next, the first method for producing a biological carrier of the present invention
An embodiment will be described with reference to FIG. First, an aqueous solution of polyvinyl alcohol (PVA solution) is prepared.
In this case, polyvinyl alcohol has a concentration of 10 to 20%.
It is advisable to add water so that the temperature of the mixture becomes, and heat the mixture to about 120 ° C. while mixing to dissolve it. The reason for selecting the concentration of polyvinyl alcohol in the above range is that the concentration of the gel is less than 10%, the strength of the gel described below is insufficient, and when it exceeds 20%, the structure of the finished carrier becomes excessively dense. This is because it becomes difficult for the required microorganisms to inhabit the internal pores.

Next, the PVA solution, the activated sludge concentrate and the dispersed particles of the synthetic resin are mixed. In this case, the mixing ratio of each component is selected so that the overall specific gravity is less than 1. For example, with respect to 100 parts by volume of the PVA solution, 100 of activated sludge concentrate having a sludge concentration of 50 to 200 g / liter is used.
50 to 200 parts by volume (20 to 50% by volume of the whole) of polymethylpentene particles having a specific gravity of about 0.8 as dispersed particles, or expanded polystyrene having a specific gravity of about 0.25. 10 to 35 parts by volume (5 to 15% by volume) of the foamed resin particles is blended to give an overall specific gravity of 0.9.
It is set to a value within the range of 2 to 0.99. In addition,
In this case, when a microorganism such as a nitrifying bacterium is planted later, the same amount of pure water is used instead of the activated sludge concentrate.

The particles of polymethylpentene or expanded polystyrene, which are the dispersed particles, have a particle size of 0.1 to 1 m.
It is suitable to be selected within the range of m. The reason why the specific gravity of the whole is set to a value within the range of 0.92 to 0.99 is that if it is out of this range, the separation characteristics of the biological carrier are deteriorated and the biological carrier remains in the separation mixed solution even after the floating separation operation. This is because it becomes easier and causes problems such as deterioration of flow uniformity in the reaction tank. FIG. 4 shows an average carrier concentration of 10 v in the reaction tank.
ol%, aeration intensity 1 m ³ Air / m ³ Hr, separation time 1 minute, is a graph showing the relationship between the specific gravity of the carrier, the carrier residual ratio% in the separation mixture and the carrier concentration% at the bottom of the reaction vessel. According to this, when the specific gravity of the carrier is less than 0.92, the carrier concentration% at the bottom of the reaction tank is reduced to 8% (corresponding to 80% of the whole) or less, and the flow uniformity is deteriorated, and the specific gravity exceeds 0.99. It can be understood that the carrier residual ratio% in the separated mixed liquid rapidly increases from 0% to 0.8% or more, and the separation characteristics deteriorate.

FIG. 5 is a graph showing the relationship between the content vol% of particles of polymethylpentene or expanded polystyrene and the finished specific gravity of the carrier in this embodiment (PVA solution concentration: 10%, activated sludge addition: none). , Gelation: freezing method, particle size: 4 mm □), and the compounding amount of polymethylpentene or expanded polystyrene can be determined in order to bring the above specific gravity range.

The mixture thus obtained is transferred to a freezing container and frozen at a temperature of -30 ° C to -20 ° C for 5 to 24 hours. After freezing, leave at -5 ° C to room temperature for 5 to 12 hours to melt. Thus, a hydrated gelation product of polyvinyl alcohol in which a myriad of fine pores containing water are formed and a predetermined microorganism propagates in the pores can be obtained.
In this case, it is preferable to repeat this freezing → thawing operation 3 to 5 times. By repeating such frozen → melting, strength of the resulting carrier, for example, from 0.5 kg / cm ² in the case of not repeated tensile strength 1 kg / cm ²
It can be improved to a certain degree.

The obtained gelled product can be taken out of the container, granulated into an appropriate size with a cutter, and then washed sufficiently with water to obtain a biological carrier on which desired microorganisms are immobilized. In this embodiment, the PVA solution is preliminarily 1 to
If 2% sodium alginate is added and the dispersed particles are mixed and then added dropwise to a 0.2 M calcium chloride solution, spherical granulation can be achieved. The biological carrier can be obtained.

In this granulation operation, the size of the biological carrier is 2 to the spherical diameter or the length of one side of the hexahedron.
It is preferable to select within a range of about 10 mm. FIG.
Is a graph showing the relationship between the particle size of the carrier and the nitrification rate in the reaction tank, and the relationship with the floating speed of the carrier (reaction tank temperature:
20 ° C, NH ₄ -N: 25 mg / liter, carrier concentration: 1
It is understood that a carrier having a particle size in the range of 2 to 10 mm is suitable because the separation characteristics are not impaired in the flotation tank and the nitrification function above a certain level can be exhibited. .

Next, the second method for producing a biological carrier of the present invention
An embodiment of the present invention will be described with reference to FIG.
After forming a film of an aqueous solution of polyvinyl alcohol on the surface of core particles of a synthetic resin, it is reacted with an aqueous solution of boric acid to gel the film so that the specific gravity is less than 1.0. First, as in the first method, the PVA solution (concentration 10
~ 20%) and prepare an equal volume of activated sludge concentrate (concentration 50
˜250 g / liter), and as a core particle of the synthetic resin, for example, polymethylpentene or foamed nylon having a specific gravity of about 0.8 or a specific gravity of 0.25.
A granular material such as expanded polypropylene or expanded polyethylene having a particle diameter of 2 to 10 mm is dipped and then pulled up to be coated with a PVA mixed liquid film having a thickness of about 0.5 to 1 mm.
Then, this is immersed in a saturated boric acid solution to form a gel, and then aged for 1 to 3 days. Then, it can be sufficiently washed with water to obtain a predetermined biological carrier.

The thickness of the PVA mixed liquid coating is 0.5 to 1
The mm is set because the habitat region of microorganisms such as nitrifying bacteria is a range from the surface of these coatings to a depth of about 0.5 mm, and therefore the above range with a slight margin is preferable. To adjust the thickness of the coating within the above range, P
Since the viscosity of the VA mixed liquid is large, excess liquid attached when the core particle is pulled up may be removed by dropping or shaking it off.

The point that the particle size of the carrier is preferably in the range of 2 to 10 mm is as described above with reference to FIG. 6, but in the embodiment using this core particle, it is shown in FIG. Graph showing the relationship between the particle size of the core granules and the specific gravity of the carrier (coating thickness: 0.5 to 1.0 mm, PVA solution: 10
%, Activated sludge: no addition, gelation: boric acid method),
When foamed nylon 71, polymethylpentene 72, foamed polypropylene 73, etc. are applied to the core particles of the above particle size, the specific gravity of 0.92, which is a preferable value, as already described.
Biological carriers in the range of -0.99 can be obtained.

As explained in detail above, according to the method for producing a biological carrier of the present invention, a biological carrier suitable for the above-mentioned flotation method can be easily produced, or the biological carrier can be prepared according to the specifications of wastewater treatment. There is an advantage that the specific gravity, particle size, shape, gelled structure and the like can be easily adjusted to suit.

[0026]

INDUSTRIAL APPLICABILITY According to the present invention, a biological carrier that can be applied to a flotation separation method utilizing a difference in specific gravity from an activated sludge mixed solution in a reaction tank while maintaining nitrification or denitrification performance as a biological carrier. Therefore, there is no need to use a precipitation separation method or a screen separation method, and naturally there is an excellent effect that problems associated with those methods can be completely avoided. Therefore, the present invention has an extremely great industrial value as a biological carrier and a method for producing the same, which solve the conventional problems.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a biological carrier of the present invention.

FIG. 2 is a flow chart showing an example of a method for producing a biological carrier of the present invention.

FIG. 3 is a flowchart showing another example of the method for producing a biological carrier of the present invention.

FIG. 4 is a graph showing the relationship between the specific gravity of the carrier and the concentration of the carrier.

FIG. 5 is a graph showing the relationship between the specific gravity of the carrier and the content of dispersed particles.

FIG. 6 is a graph showing the relationship between the particle size of a carrier and its floating speed.

FIG. 7 is a graph showing the relationship between the particle size of the core particles and the specific gravity of the carrier.

FIG. 8 is a sectional view showing a main part of a conventional wastewater treatment facility.

FIG. 9 is a sectional view showing the principle of a flotation tank.

[Explanation of symbols]

2,3 hydrated gel, 21 dispersed particles, 31 core particles.

Claims (10)

[Claims] 1. A hydrated gel product of polyvinyl alcohol containing dispersed particles of a synthetic resin, having a specific gravity of 1.0.
A biological carrier that is less than. 2. The dispersed particles are particles of polymethylpentene or a foamed resin, and the specific gravity of the granules of the hydrated gel is within the range of 0.92 to 0.99. The described biological carrier. 3. A biological carrier comprising a core particle of a synthetic resin coated with a hydrated gel of polyvinyl alcohol and having a specific gravity of less than 1.0. 4. The core particle is made of expanded polypropylene, expanded polyethylene, polymethylpentene or expanded nylon particles, and has a specific gravity in the range of 0.92 to 0.99. Biological carrier. 5. A biological carrier characterized in that dispersed particles of a synthetic resin are added to and mixed with an aqueous solution of polyvinyl alcohol, and then frozen and thawed repeatedly to form a hydrated gelled product having a specific gravity of less than 1.0. Production method. 6. The method for producing a biological carrier according to claim 5, wherein activated sludge is added and mixed together with the dispersed particles of the synthetic resin to the aqueous solution of polyvinyl alcohol. 7. The biological carrier according to claim 5, wherein the dispersed particles are particles of polymethylpentene or a foamed resin, and a hydrated gelled product having a specific gravity within the range of 0.92 to 0.99 is formed. Production method. 8. A coating of an aqueous solution of polyvinyl alcohol is formed on the surface of core particles of a synthetic resin, and then contacted with an aqueous solution of boric acid to form the hydrated gel product, and
A method for producing a biological carrier, characterized in that the entire specific gravity is less than 1.0. 9. The method for producing a biological carrier according to claim 8, wherein a film of an aqueous solution of polyvinyl alcohol mixed with activated sludge is formed. 10. The core particle is expanded polypropylene,
The method for producing a biological carrier according to claim 8 or 9, which is a granular body of expanded polyethylene, polymethylpentene or expanded nylon, and has a specific gravity of 0.92 to 0.99 as a whole.