JPH10314782A - Water treatment carrier, its production method and nitrification denitrification method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute simultaneously nitrification and denitrification of organic wastewater by constituting so that a microbe having nitrification function lives near a surface of a carrier, and a microbe having a denitrification function lives near a central part. SOLUTION: For the water treating carrier, acetal-made PVA or polyethylene glycol water-containing gel having a network structure on a surface or inside is used. In this carrier, a microbe having a nitrification function lives near the surface of the carrier, and a microbe having a denitrification function lives near a central part. In order to manufacture such the carrier, for example, PVA is brought in contact with the microbe having denitrification function such as Pseudomonas denitrificans or the like, brought in contact with the microbe having nitrification function such as Nitrosomonas or the like after the microbe having denitrification function enters an inside of the carrier, and cultured to obtain such the carrier. Since the carrier has both of the nitrification function and the denitrification function, nitrification and denitrification can be simultaneously executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for water treatment, a method for producing the same, and a method for nitrification and denitrification using the same. More specifically, microorganisms having nitrifying ability inhabit near the surface,
A water treatment carrier comprising an acetalized polyvinyl alcohol-based hydrogel or polyethylene glycol-based hydrogel in which microorganisms having a denitrifying ability inhabit in the vicinity of the center, a method for producing the same, and use thereof The nitrification and denitrification method.

[0002]

2. Description of the Related Art Conventionally, organic wastewater containing nitrogen compounds, such as rural settlement wastewater, household wastewater, urban wastewater, fish culture wastewater and various industrial wastewater, generally uses aerobic microorganisms and anaerobic microorganisms. It has been treated by methods of purifying pollutants. For example, as shown in FIG. 1, the wastewater flows into the anaerobic tank 1 to remove most of the BOD components, and then oxidizes the remaining BOD components under aerobic conditions in the aerobic tank 2 and removes nitrogen compounds by nitrifying bacteria. Nitrification is performed, a part of the treated water flowing out of the aerobic tank 2 is circulated to the anaerobic tank 1, and denitrification is removed using denitrifying bacteria under anaerobic conditions, and the effluent from the remaining aerobic tank is settled. The sludge was settled and separated in the tank 3 and then discharged.

In recent years, studies have been made to reduce the size of a wastewater treatment apparatus by filling a processing tank with a carrier to which microorganisms adhere and proliferate. As such a carrier, various types of granular materials such as ceramics and plastics, and honeycombs have been proposed. -Like structures have been developed. The carrier used for wastewater treatment is required to have a high water content, excellent oxygen and substrate permeability, high affinity with living organisms, etc. Various types of polymer carriers have been proposed as examples, and examples thereof include polyvinyl alcohol-based hydrogels.

A water-containing gel of polyvinyl alcohol (hereinafter, polyvinyl alcohol is abbreviated as PVA) is prepared by bringing an aqueous mixed solution of PVA and sodium alginate into contact with an aqueous calcium chloride solution to form a sphere, followed by freezing and thawing (Japanese Patent Laid-Open No. Sho 64). No. 43188), a method of bringing a PVA aqueous solution into contact with a saturated boric acid aqueous solution to form a hydrous gel (Sewer Association of Japan, Vol. 23 (1986) p41;
Vol. 30 (1986) p36), a method of injecting a PVA aqueous solution into a mold and then performing a partial dehydration by freezing (JP-A-58-366)
No. 30 publication), and such PVA hydrogel is known to be used for water treatment.

[0005] However, in these organic wastewater treatments, an aerobic tank for the nitrification reaction and an anaerobic tank for the denitrification reaction are separately arranged. Therefore, the carrier must be separately charged into each tank. Therefore, miniaturization of the apparatus has its limits. If a carrier capable of simultaneously performing nitrification and denitrification can be used, it is extremely efficient and the apparatus can be made compact.

On the other hand, it has already been proposed to simultaneously perform nitrification and denitrification.
The publication has a point that the shortest distance to the surface is 2 mm or more inside the hydrogel, aerobic bacteria are fixed near the surface, and PVA in which anaerobic bacteria are fixed near the center is the main component. JP-A-8-224076 discloses a carrier in which microorganisms such as ammonia-oxidizing bacteria and / or denitrifying bacteria are immobilized on a synthetic polymer carrier such as a photocurable resin. Is formed into a tube shape, a film shape, or the like.

[0007]

However, since the carrier disclosed in Japanese Patent Application Laid-Open No. Hei 5-130867 is a hydrogel produced by freezing and thawing, the obtained hydrogel has a dense layer. The dense layer becomes a barrier,
It is difficult for microorganisms capable of denitrification (hereinafter, referred to as denitrifying bacteria) to enter inside. Therefore, in order to obtain a carrier in which denitrifying bacteria live inside using such a hydrogel, It is necessary to use a so-called entrapment fixing method in which denitrifying bacteria are produced by entrapping them in a carrier.

[0008] The carrier disclosed in Japanese Patent Application Laid-Open No. H8-224076 is also one in which bacteria are entrapped and immobilized on a synthetic polymer carrier, which is further molded.
There are difficulties that cannot be easily manufactured. Accordingly, an object of the present invention is to provide an acetalized PVA-based hydrous gel or polyethylene glycol-based gel that can be produced without entrapping and fixing bacteria and can simultaneously perform nitrification and denitrification of organic wastewater. Another object of the present invention is to provide a water treatment carrier comprising a hydrogel and a method for producing the same, and a nitrification denitrification method using the same.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies and have used as a carrier a PVA-based hydrogel or a polyethylene glycol-based hydrogel having a network structure on the surface and / or inside. If there is no dense layer that prevents the invasion of denitrifying bacteria, the denitrifying bacteria can easily inhabit inside the carrier, and microorganisms having nitrification ability (hereinafter referred to as nitrifying bacteria) can easily invade on the carrier surface. It has been found that nitrification and denitrification can be carried out simultaneously, leading to the present invention. That is, the present invention relates to a carrier comprising an acetalized PVA-based hydrogel or a polyethylene glycol-based hydrogel having a network structure on the surface and / or inside, and having a nitrification ability near the surface of the carrier. A carrier for water treatment, wherein microorganisms inhabit, and microorganisms having a denitrifying ability inhabit in the vicinity of the center.

Another aspect of the present invention is to provide a method comprising contacting an acetalized PVA-based hydrogel or a polyethylene glycol-based hydrogel with a microorganism having a denitrifying ability, and the microorganism invading the interior of the hydrogel. A water treatment carrier comprising an acetalized PVA-based hydrogel or a polyethylene glycol-based hydrogel, which is brought into contact with a microorganism having a nitrifying ability, and the microorganism inhabits near the surface of the hydrogel. It is a manufacturing method.

[0011] Still another invention of the present invention is an acetalized PVA-based hydrogel in which microorganisms having nitrifying ability inhabit near the surface and microorganisms having denitrifying ability inhabit in the vicinity of the center. Alternatively, a nitrification denitrification method characterized by simultaneously performing nitrification denitrification of organic wastewater using a water treatment carrier comprising a polyethylene glycol-based hydrogel.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. The carrier for water treatment of the present invention has a network structure on the surface and / or inside. As the carrier having such a structure, acetalized PVA or a polyethylene glycol-based hydrogel is used. Acetalized PVA hydrogel or polyethylene glycol-based hydrogel has a network structure on the surface and inside of the carrier, and does not have a dense layer that serves as a barrier when bacteria enter, so that denitrifying bacteria are contained inside. Since it is easy to enter and nitrifying bacteria easily inhabit on the surface, it becomes a carrier suitable for the purpose of the present invention and is easy to manufacture. The carrier of the present invention is excellent as a carrier for water treatment because it has excellent ability to remove organic compounds and excellent mechanical strength.

When the average degree of polymerization and / or saponification degree of PVA is higher, the concentration of PVA can be reduced, so that the water content of the hydrogel can be increased. . From this point, PVA
The average degree of polymerization is preferably 1,000 or more, more preferably 1500 or more. Further, the degree of saponification of PVA is preferably 95 mol% or more, particularly preferably 9 mol%.
More than 8 mol% is more preferable.

The concentration of PVA is preferably large from the viewpoint of the strength of the carrier, and is preferably small from the viewpoint of microbial habitat. Therefore, the concentration is preferably 1 wt% to 40 wt%, more preferably 3 wt% to 2 wt%.
0 wt% is more preferable.

In the present invention, PVA is acetalized in order to prevent elution or deterioration of PVA, and formaldehyde and glyoxal are used as acetalizing agents.
, Glutaraldehyde, benzaldehyde, succinaldehyde, malondialdehyde, adipaldehyde, terephthalaldehyde, ω, ω'-nonandial, and the like. Polyvinyl formal is a preferred example of such an acetalized PVA. If the degree of acetalization is too low, the water resistance will be low, and if it is too high, it will be hydrophobized and the inhabitation of microorganisms will deteriorate, so it is preferably from 10 to 60 mol%, more preferably from 20 to 55 mol%.

Examples of the acid used for acetalization include acids such as sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, acetic acid and oxalic acid, and acidic salts such as sodium hydrogen sulfate and ammonium hydrogen sulfate. Is also used. In the presence of an aldehyde compound or acid, the hydrogel may overswell or dissolve, so that sodium acetate or the like, which has the effect of synthesizing PVA, is added to the acetalization solution as an inhibitor. You may.

As long as the acetalization of PVA is not inhibited, for example, molding aids such as sodium alginate, carrageenan, boric acid, and two or more kinds of carbonate ions, hydrogen carbonate ions, sulfate ions, phosphate ions, etc. A monovalent or polyvalent anion for phase separation of the polymer may be added.
The acetalized PVA-based hydrated gel has an uneven surface and a communication hole from the surface to the center, so that it can be effectively used not only on the surface but also on the inside.

The acetalized PVA hydrogel is separated from the acetalized solution, subjected to a treatment such as washing or neutralization, and becomes a carrier which can be used for wastewater treatment. The hydrogel carrier may be dried once. When immersed in water, it becomes a hydrogel again. The higher the water content, the better, and 50 to 50% by wet weight.
It is preferably 99%, more preferably 60 to 98%. The method for measuring the moisture content based on wet weight is as follows.
After immersion in water at 24 ° C. for 24 hours or more, the weight of the carrier excluding water adhering to the surface is measured (wet weight), and after drying at 105 ° C. for 4 hours, the weight is measured (dry weight). The moisture content based on wet weight is {(wet weight−dry weight) / wet weight} × 100
(%).

The most preferred acetalized PVA hydrated gel has a surface having an average diameter of 10 to 100 μm and a depth of 10 to 100 μm in a concave portion having a length of 1 mm, which has already been filed by the applicant as Japanese Patent Application No. 9-11057. 1 per
Acetator having 0 or more and having a water content of 50% by weight or more
Hydrated PVA hydrogel. The method for producing this hydrogel is described in detail in the above specification, but, for example, a P having an average degree of polymerization of 1700 and a degree of saponification of 99.8 mol% can be mentioned.
A mixed aqueous solution of 8 wt% of VA, 1 wt% of sodium alginate and 0.3 wt% of sodium hydrogen carbonate is prepared, and the aqueous solution is dropped into a 0.1 mol / L (L) aqueous solution of calcium chloride to obtain a spherical molded product. Then, formaldehyde 20g / L, sulfuric acid 200g / L
L, 100 g / L sodium sulfate can be obtained by immersion in an aqueous solution for acetalization and washing with water. Such a P
As described above, the VA hydrogel has a network structure on the surface and inside of the carrier. The presence of a network structure on the surface and inside of the carrier can be confirmed by a scanning electron microscope.

Polyethylene glycol-based hydrogel is also B
It is excellent in OD removal ability, nitrification ability and denitrification ability, and is a suitable carrier. The polyethylene glycol hydrated gel can be obtained, for example, by the method disclosed in Japanese Patent Publication No. 6-32615.

The carrier for water treatment of the present invention comprises, as described above,
Microorganisms having nitrification ability live near the surface of the carrier, and microorganisms having denitrification ability live near the center. In order to manufacture such a carrier for water treatment, for example, the above PVA is prepared by using Pseudomonas denitrificans (Pseudomo).
nitrosomonas (Nitrosomnas) after the microorganisms having a denitrifying ability are brought into contact with a microorganism having a denitrifying ability such as nas denitrificans.
By contacting and acclimating with a microorganism having a nitrifying ability such as onas), a carrier in which a microorganism having a nitrifying ability inhabits near the surface and a microorganism having a denitrifying ability inhabits near the center can be obtained.

As another method, a method may be employed in which a carrier such as PVA is brought into contact with microorganisms such as general activated sludge and then aerated with water containing ammonia nitrogen. According to this method, the surface of the carrier is an aerobic atmosphere, so that nitrifying microorganisms are dominant.On the other hand, the vicinity of the center of the carrier is an anaerobic atmosphere, and the microorganisms that have entered the inside are microorganisms capable of denitrification. Because it will be dominant,
In the present invention, microorganisms having nitrifying ability inhabit near the surface,
A water treatment carrier in which microorganisms having a denitrifying ability inhabit in the vicinity of the center can be obtained.

In the water treatment carrier of the present invention, nitrifying bacteria inhabit near the surface and denitrifying bacteria inhabit near the center. In the present invention, the meaning of the vicinity of the surface and the vicinity of the center is not strictly defined, but the meaning of the vicinity of the surface is approximately 10% from the surface.
And the vicinity of the center is approximately 90 degrees from the center.
%. The distribution of nitrifying bacteria and denitrifying bacteria is not completely separated, and there may be a region where both bacteria are mixed to some extent as long as they have nitrifying ability and denitrifying ability as a carrier.

The fact that microorganisms having nitrification ability inhabit near the surface and microorganisms having denitrification ability inhabit in the vicinity of the center can be confirmed, for example, by the FISH method using a gene probe (fl
urescent in situ hybridi
zation). That is, the FISH method is a method utilizing a gene probe that specifically binds to a gene of a target microorganism. Such a gene probe is prepared, and one end of the gene probe is FITC. Specific microorganisms can be detected by labeling with such a fluorescent dye.

The shape of the acetalized PVA hydrogel is not particularly limited, and a gel formed into an arbitrary shape such as a fibrous shape, a dice shape, a film shape, a columnar shape, a hollow cylindrical shape, a spherical shape, and a disk shape is used. However, spherical ones are preferred from the viewpoint of the fluidity of the carrier.

Since the water treatment carrier of the present invention has a nitrifying ability and a denitrifying ability, the nitrifying and denitrifying reactions can be carried out simultaneously. That is, by flowing the water treatment carrier of the present invention under an aerobic atmosphere, a nitrification reaction occurs,
Further, since a denitrification reaction occurs inside the carrier, water treatment such as wastewater treatment can be rationally performed in one reactor, and the apparatus can be made compact.

Conventionally, purification of water systems inhabited by fish has been carried out by physical filtration for removing solids such as food leftovers and excrement, and ammonia generated from food leftovers and excrement by feeding microorganisms on carriers. There is a biofiltration that converts nitrogen into nitrate. Biofiltration aims to nitrify ammonia nitrogen, which is harmful to fish, into nitrate nitrogen, which is relatively harmless.If nitrification of ammonia nitrogen continues, nitrate nitrogen will continue to increase, eventually causing fish It will be harmful and water must be replaced.

The water treatment carrier of the present invention can also be suitably used for purifying such a fish-inhabiting water system. In other words, the present invention can be used for general purification of water systems inhabited by fish, such as purification of aquariums for aquaculture and ornamental fish, purification of fish cages and aquaculture water areas, purification of live fish transport water, and the like.

[0029]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. Example 1 6 wt% of PVA (average degree of polymerization 1700, degree of saponification 99.8 mol%) manufactured by Kuraray Co., Ltd., sodium alginate 1
An aqueous solution consisting of wt% and 0.35 wt% of sodium hydrogen carbonate was prepared. This aqueous solution was supplied to a roller pump equipped with a silicon tube having an inner diameter of 4 mm equipped with a nozzle having an inner diameter of 3 mm at the tip thereof to obtain 5 ml (mL).
/ Min, and agitated with a stirrer at a concentration of 0.1
It was added dropwise to an aqueous solution of calcium chloride at mol / liter (L). The dropped droplets became spherical and settled in the calcium chloride aqueous solution.

[0030] The spherical molded product was treated with formaldehyde 20
g / L, sulfuric acid 200g / L, sodium sulfate 90g / L
Immersed in a 40 ° C. aqueous solution for 70 minutes, washed with water,
Thus, a spherical hydrogel having a thickness of 0.3 mm was obtained. The degree of acetalization of this hydrogel was 39 mol%, and the water content was 93%. As a result of observation with an optical microscope and an electron microscope, the surface and the inside of the acetalized PVA carrier have a network structure, and have a diameter of 1 to 10 from the carrier surface to the center.
There were countless μm communication holes.

5 kg of this carrier is added to 10 L (MLSS 3000 ppm) of sludge containing microorganisms having a denitrifying ability.
After immersion for a day, the carrier was taken out, put into 10 L of waste water adjusted to 100 ppm of TOC and 100 ppm of nitrate nitrogen, and stirred to the extent that air was not involved. After about three days, the amount of nitrate nitrogen became almost 0 ppm, and it was confirmed that the carrier had a denitrifying ability.

Further, this carrier is added to 10 L of sludge (MLSS 3000 ppm) in which microorganisms having nitrification ability are present.
It was immersed for a day and aerated. The carrier was taken out, put into 10 L of waste water adjusted to 50 ppm of ammonia nitrogen, and aerated.
After about one week, the amount of ammonia nitrogen became almost 0 ppm, and it was confirmed that the carrier had a nitrifying ability.

This carrier was placed in a 10 L aeration tank,
Wastewater adjusted to 100 ppm of C and 50 ppm of ammonia nitrogen was supplied at 2 L / hour. Dissolved oxygen is 1-3 ppm
The aeration amount was adjusted so that After a lapse of 10 days, the quality of the treated water was measured.
m, nitrite nitrogen 0.2 ppm, nitrate nitrogen 4.9 pp
m, the TOC was 5.1 ppm, and the nitrification and denitrification treatment was successfully performed.

This carrier was placed in a 100 L aeration tank, and this aeration tank was connected to a 1 m ³ water tank (100 fish).
Water was circulated at 10 L / min. After one month, when the water quality was measured, it was 0.1 ppm ammonia nitrogen, 0 ppm nitrite nitrogen, and 5.3 ppm nitrate nitrogen, and the water quality was good. No fish died.

Example 2 As PVA, the average degree of polymerization was 4000 and the degree of saponification was 99.8.
An aqueous solution consisting of 5% by weight of PVA, 1% by weight of sodium alginate, and 0.25% by weight of sodium sulfate was brought into contact with a 0.1 mol / L aqueous solution of calcium chloride to form a sheet. This is formaldehyde 20
g / L, sulfuric acid 200g / L, sodium sulfate 100g /
L was immersed in a 40 ° C. aqueous solution for 60 minutes, and then washed with water. This was cut into a die having a diameter of about 5 mm and observed with an electron microscope. As a result, it was confirmed that the mesh had a network structure on the surface and inside. Was found to have

1 kg of this carrier was used for 10 L of activated sludge (MLSS5) collected from a wastewater treatment tank at the Kuraray Okayama Plant.
000 ppm) for 3 days, put into a 10 L aeration tank, TOC 100 ppm, ammonia nitrogen 50 pp
m was supplied at a rate of 2 L / hour. Dissolved oxygen is 1
The aeration amount was adjusted so as to be 3 ppm. After 30 days, the quality of the treated water was measured to be 0.0 ppm of ammoniacal nitrogen, 0.1 ppm of nitrite nitrogen, 6.2 ppm of nitrate nitrogen, and 5.5 ppm of TOC. did it.

5 kg of this carrier was used for 100 L of activated sludge (MLSS) collected from a wastewater treatment tank at the Kuraray Okayama Plant.
5,000 ppm) for 3 days, and then put in a 100 L aeration tank, and this aeration tank and a 1 m ³ water tank (100 fish
And the water was circulated at 10 L / min. After one month, when the water quality was measured, ammonia nitrogen 0.1p
pm, nitrite nitrogen 0.0 ppm, nitrate nitrogen 8.7
ppm and good water quality. No fish died.

Example 3 As PVA, the average degree of polymerization was 1700 and the degree of saponification was 99.8.
An aqueous solution consisting of 6 wt% of PVA and 1 wt% of sodium alginate was dropped into a 0.1 mol / L aqueous solution of calcium chloride to form a spherical shape.

This spherical molded product was treated with formaldehyde 18
g / L, sulfuric acid 210 g / L, sodium sulfate 100 g /
L was immersed in an aqueous solution of 40 ° C. for 60 minutes and washed with water to obtain a flexible spherical hydrogel having a diameter of about 5 mm. The degree of acetalization of this hydrogel was 39 mol%, and the water content was 93%.
Met. As a result of observation with an optical microscope and an electron microscope, it was observed that the surface and the inside of the carrier had a network structure, and there were countless communication holes having a diameter of 1 to 10 μm from the surface of the carrier to the center.

5 kg of this carrier was added to 100
L, and the aeration tank was connected to a 1 m ³ water tank (100 fish), and water was circulated at 10 L / min. After one month, when the water quality was measured, it was 0.1 ppm ammonia nitrogen, 0 ppm nitrite nitrogen, and 7.6 ppm nitrate nitrogen, and the water quality was good. No fish died.

[0041]

According to the present invention, it is possible to provide a carrier comprising an acetalized PVA-based hydrogel or a polyethylene glycol-based hydrogel having a nitrifying ability and a denitrifying ability. According to the carrier of the present invention, it has both functions of nitrification and denitrification, and can simultaneously perform nitrification and denitrification of organic wastewater. can do.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a conventional organic wastewater treatment apparatus.
It is.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anaerobic tank 2 Aerobic tank 3 Sedimentation tank 4 Organic drainage 5 Air diffuser 6 Treated water

Claims (4)

[Claims] 1. A carrier comprising an acetalized polyvinyl alcohol-based hydrogel or a polyethylene glycol-based hydrogel having a network structure on the surface and / or inside thereof, wherein nitrification occurs near the surface of the carrier. A carrier for water treatment, wherein microorganisms having the ability are inhabited and microorganisms having the denitrification ability inhabit in the vicinity of the center. 2. Acetalized polyvinyl alcohol
2. The carrier for water treatment according to claim 1, wherein the water-containing gel is a polyvinyl formal water-containing gel. 3. Acetalized polyvinyl alcohol
A hydrogel of polyethylene type or a hydrogel of polyethylene glycol type with a microorganism having a denitrifying ability, and after the microorganisms enter the interior of the hydrogel, contact with a microorganism having a nitrifying ability, thereby bringing the microorganism into the vicinity of the surface of the hydrogel. A method for producing a water treatment carrier comprising an acetalized polyvinyl alcohol-based hydrogel or a polyethylene glycol-based hydrogel, wherein the water-treating carrier is acetalized. 4. Acetalized polyvinyl alcohol-based hydrogel or polyethylene glycol-based microorganism in which a microorganism having a nitrifying ability inhabits near the surface and a microorganism having a denitrifying ability inhabits near the center. A nitrification and denitrification method for organic wastewater using a water treatment carrier comprising a water-containing gel.