JP3265981B2 - Entrapping immobilization carrier for nitrogen removal and method for forming the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an entrapping immobilization carrier for nitrogen removal and a method for forming the same, and more particularly to a nitrogen removal entrapping and fixing activated sludge containing nitrifying bacteria and denitrifying bacteria used for nitrification and denitrification reactions. The present invention relates to an entrapping immobilization carrier for use and a method for forming the same.

[0002]

2. Description of the Related Art Wastewater treatment using an entrapping immobilization carrier in which microorganisms are entrapped and immobilized in a polymer hydrogel has characteristics such as improvement of treatment efficiency, downsizing of a reaction tank, and reduction of generated sludge.

[0003] The entrapping immobilization carrier is usually prepared by cutting a suspension obtained by suspending activated sludge in a gel raw material such as polyacrylamide or polyvinyl alcohol into a predetermined size after gelling the suspension with a polymerization agent. It is formed by pelletizing.

[0004] This entrapping immobilization carrier selectively immobilizes microorganisms at a higher concentration than a biofilm-type immobilization method of adhering microorganisms to the surface, such as sand, activated carbon, and ceramics. For this reason, it has attracted attention as a method for immobilizing nitrifying bacteria having a small growth ability.

[0005] The entrapping immobilization carrier entrapping and immobilizing nitrifying bacteria has already been put to practical use in the nitrification step for removing ammonia nitrogen in wastewater. Practical application is also being considered.

Incidentally, in order to enhance the nitrogen removal effect in the nitrification / denitrification step, the nitrification rate in the nitrification step is increased to efficiently nitrify ammoniacal nitrogen into nitrite ions or nitrate ions, It is necessary to increase the denitrification rate in the nitrification step to efficiently denitrify nitrite ions and nitrate ions generated in the nitrification step. In particular, since nitrite ions are toxic to microorganisms, reducing them to nitrogen gas is effective in increasing the activity of microorganisms.

For this purpose, it is necessary to keep nitrifying bacteria or denitrifying bacteria at a high concentration in the carrier, and it is important to efficiently flow the carrier in the reaction tank to increase the contact efficiency with the wastewater. .

[0008]

However, the conventional carrier has not been sufficient in the following points. If the denitrification process is not sufficiently performed in the denitrification process, particularly toxic nitrite ions will be released in a state where they remain,
There is a need for a carrier that can more efficiently remove nitrite ions. If the carrier is broken by collision of the carriers flowing in the reaction tank, the quality of the treated water tends to be turbid and the abrasion resistance is not sufficient. Conventional carriers have poor mixing properties between the sludge and the gelling agent, and a material composition that is easy to form is desired. The specific gravity of the carrier is usually about 1.03. However, if a worm is attached to the wastewater in the wastewater treatment, the apparent specific gravity becomes light and floats on the water surface, resulting in poor fluidity in the reaction tank. Disadvantage.

The present invention has been made in view of such circumstances, and simultaneously solves a plurality of problems of improving nitrogen removal performance and abrasion resistance, and further improving moldability in molding a carrier by a simple method. It is an object of the present invention to provide an entrapping immobilization carrier for removing nitrogen and a method for forming the same.

[0010]

According to the present invention, in order to achieve the above object, an activated sludge containing nitrifying bacteria and denitrifying bacteria is entrapped and fixed in a polymer hydrogel to form a entrapped fixed carrier for nitrogen removal .
In addition, the polymer hydrogel contains at least one metal oxide fine powder selected from iron oxide and silicon oxide.

[0011] Further, the present invention provides
Activated sludge containing nitrifying bacteria and denitrifying bacteria and metal oxide fine powder were mixed and allowed to stand for 1 to 2 hours. A mixed solution was suspended in a gel raw material solution to prepare a suspension. It is characterized in that

According to the present invention, nitrifying bacteria and denitrification can be carried out by a simple method of including a metal oxide fine powder containing iron oxide, silicon dioxide or a mixture thereof as a main component in a polymer hydrogel.
Enhance the activity of denitrifying bacteria, it can improve the abrasion resistance of the water-containing gel, more excellent in formability with enhanced nitrogen removal performance in the wastewater nitrogen
An entrapping immobilization carrier for removal can be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a nitrogen-containing entrapping immobilization carrier and a method for forming the same according to the present invention will be described below in detail with reference to the accompanying drawings.

[0014] The inventors of the present invention, when forming the entrapping immobilization carrier for nitrogen removal, by containing a predetermined amount of a metal oxide fine powder containing iron oxide, silicon dioxide or a mixture thereof as a main component. It can increase the activity of nitrifying bacteria and denitrifying bacteria , improve the abrasion resistance of hydrous gel, and further improve the nitrogen removal performance in wastewater to obtain an encapsulating immobilized carrier for nitrogen removal with excellent moldability. The present invention has been made based on such findings by finding out unexpected facts.

FIG. 1 is a flow chart showing an example of a method for forming the entrapping immobilization carrier for removing nitrogen according to the present invention.
In this case, a cylindrical pellet having a length of 3 mm and a diameter of 3 mm is formed.

As shown in FIG. 1, a concentrated activated sludge and a metal oxide fine powder are mixed to prepare a mixed liquid, and the mixed liquid is left for 1 to 2 hours. On the other hand, a gel raw material liquid is prepared by adjusting a mixture of a polyethylene glycol prepolymer (hereinafter, referred to as PEG) as a hydrogel and NNN'N '@ tetramitylethylenediamine as a polymerization agent to pH 7.5. Next, a suspension was prepared by suspending the mixed solution in the gel raw material solution, potassium persulfate was added as a polymerization initiator to the suspension, and the mixture was immediately poured into a vinyl chloride tube having an inner diameter of 3 mm and heated at 20 ° C. Gel for 10 minutes. next,
The gelled rod-shaped column is cut into a length of 3 mm to form a pellet-shaped entrapping immobilization carrier for removing nitrogen .

In this method for forming the entrapping immobilization carrier for removing nitrogen , the mixed particles of activated sludge containing nitrifying bacteria and denitrifying bacteria and metal oxide fine powder are allowed to stand for 1 to 2 hours, whereby powder particles are activated. Evenly dispersed in sludge. This dispersed mixture has a viscosity suitable for handling. This was suspended in a gel raw material solution to prepare a suspension, and the suspension was gelled, so that the content of the metal oxide can be made uniform when pelletized.

The metal oxide fine powder used in the present invention preferably contains iron oxide, silicon oxide, a mixture of iron and silicon as a main component, and has an average particle size of 5 to 40 μm. As a raw material of the iron oxide, oxides such as ferrite and magnetite recovered from a steel pickling wastewater discharged from an ironworks can be used. As a raw material of silicon oxide, a viscous powder such as kaolin, monlonite, or pyrophyllite used in the ceramic industry is used. As a mixture of iron and silicon, fly ash separated and removed from flue gas of a coal combustion furnace or a sludge combustion furnace can be used.

When a metal oxide having an average particle diameter in the range of 5 to 40 μm is used, the metal oxide easily mixes with the activated sludge and maintains a uniform and stable suspension state. If the particle size is smaller than the above range, it is easy to form a lump of powder when mixed,
If it is too large, some of the particles will settle out and become non-uniform when molded with a gelling agent.

The addition amount of the metal oxide is preferably at least 5% by weight of the water-saturated hydrogel in view of improving the strength of the hydrogel. In terms of nitrogen removal performance,
It is preferably at least 6% by weight for increasing the number of denitrifying bacteria, and more preferably at least 10% for increasing the number of denitrifying bacteria remarkably.

The increase in strength and the number of bacteria is proportional to the amount added, but at the same time the specific gravity increases. If a heavy hydrogel is to be suspended in the liquid, the amount of aeration must be increased accordingly, so that the practical limit is 20%. For example, the specific gravity of the polyvinyl alcohol hydrogel containing sludge is 1.02, and the sedimentation speed when dropped into water is about 3.
3 cm / sec. When 10% of iron oxide powder is added, the specific gravity becomes about 1.09, the sedimentation velocity is 6.1 cm / sec, and when the addition amount of iron oxide is 20%, the apparent specific gravity is 1.17 and the sedimentation velocity is 9 .9 cm / sec.

When used in an upwardly packed packed bed or fluidized bed, the apparent specific gravity is preferably large, but when fluidized by aeration, the apparent specific gravity is suitably about 1.1 or less.

[0023] In the interior of the well-acclimated treated water-containing gel nitric
It is inferred from observations with an electron microscope and the like that the germs and the denitrifying bacteria form colonies and cause an active biological reaction. However, in concentrated sludge, several to several tens of cells are loosely connected and separated and aggregated repeatedly. When silicon dioxide having an average particle size of 10 μm is added to this concentrated sludge, silicon dioxide is generated between a group of cells of nitrifying bacteria and denitrifying bacteria ,
Disperses into a stable suspension. If you leave the suspension was left for a while, the size of the group of nitrifying bacteria and denitrifying bacteria is substantially added metal oxides size and nitrifying bacteria and denitrifying bacteria becomes comparable
Of bacteria are strengthened. Nitrifying bacteria and denitrifying bacteria are poisoned by organic solvents and catalysts contained in the gelling agent, and the number of bacteria is greatly reduced during gel formation. However, the addition of metal oxide particles mitigates the effects of poisoning and shortens the initial startup time of the entrapping immobilization carrier for nitrogen removal . In addition, the cell density, particularly the number of denitrifying bacteria, is increased by a factor of ten or more by adding metal oxides, and nitrite and nitric acid generated by nitrifying bacteria can be rapidly reduced to nitrogen.

There is no particular limitation on the hydrogel used when the immobilizing carrier for removing nitrogen is formed. For example, polyacrylamide, carrageenan, agar, polyvinyl alcohol, sodium alginate and the like can be used. Further, the polymerization agent and the polymerization initiator are not limited to the above agents.

[0025]

FIG. 2 shows that the metal oxide content is 5, 10, 15 or less by the method of the present invention described in the above embodiment.
It is physical property data of the nitrogen- containing entrapping immobilization carrier molded to 20% and data for determining a preferable content of the metal oxide. Table 1 shows nitrogen removal according to the present invention.
Fig. 3 shows the composition ratio of the composition for forming the entrapping immobilization carrier for leaving . Then, the specific gravity, the sedimentation velocity, and the compressive strength as an index of abrasion resistance were examined for each of the nitrogen- immobilized encapsulation-immobilized carriers. The comparative example in FIG. 2 is a conventional product which does not contain a metal oxide but is formed in the same manner as other compositions.

[0026]

[Table 1] Examples of the metal oxide of this example include iron oxide (contents of 5, 1
5%), kaolin (contents 10, 20%) and fly ash (contents 5 to 20%). Regarding fly ash, two types of fly ash (A) having a silicon dioxide content of 50% and fly ash (B) having a silicon dioxide content of 47% were used. There are two types of pellet shapes of the entrapping immobilization carrier: a 3 mm square die pellet and a 3 mm φ × 3 mm columnar pellet.

The abrasion resistance was evaluated by measuring the compressive strength. The compressive strength was measured by using a rheometer and gradually applying pressure to the pellet surface to measure the pressure (kg) at which the pellet was broken.
m ² ) to calculate the compressive strength (kg / cm ² ).

From the results shown in FIG. 2, first, the measures against the hanging insects will be discussed.

In the meantime, in the measures against the rodent insects which the present inventors conducted an experiment, the sedimentation speed of the carrier was set to about 5 to 8 (cm / sec) in a state where the rodent was not attached. It is found that the fluidity is appropriate in terms of fluidity, and the specific gravity is about 1.07 to 1.14.

According to the results shown in FIG. 2 based on the above findings, when iron oxide and fly ash are used as the metal oxide, if the content is 10% or less, a sufficient sedimentation velocity or specific gravity at the time of sticking of the worm is sufficient. Cannot be obtained, and if it is 20% or more, the energy consumption for flowing the entrapping immobilization carrier for nitrogen removal becomes large. In the case of kaolin, since the specific gravity of kaolin itself is light, addition of 20% or more is also possible.

Next, looking at the compressive strength which affects the abrasion resistance of the entrapping immobilization carrier for removing nitrogen from the results of FIG. 2, the conventional product having a content of 0% has a compressive strength of 2-3 kg. /
cm ² , and this degree of compressive strength has a disadvantage that it is easily damaged by long-term use. On the other hand, the entrapping immobilization carrier for nitrogen removal of the present invention containing a metal oxide increases in proportion to the content, and even at a 5% content, obtains about 1.5 times the compressive strength of the conventional product. I was able to. When the content is examined in consideration of the result of the compressive strength and the result of the measures against the hanging insect, the content is preferably 5% to 20%, and more preferably 10% to 20%.

FIG. 3 shows that the activated sludge at the sewage treatment plant is used as a seed fungus to form a nitrogen- added entrapping immobilization carrier to which metal oxide has been added according to the method of the present invention, and that it has been acclimated in ammonia water for 2 months. It is a result of examining the densities of the respective numbers of nitrifying bacteria, denitrifying bacteria, and general bacteria in the entrapping immobilization carrier for removing nitrogen . As the metal oxide, fly ash containing silicon dioxide and iron oxide as main components was used.
% For two levels. As a comparative example, a conventional product to which no metal oxide was added was used.

According to FIG. 3, the number of bacteria of the conventional product was 10 ⁸ for both nitrifying bacteria and denitrifying bacteria, and 5 × 10 ⁸ for general bacteria. On the other hand, the number of bacteria of the entrapping immobilization carrier for nitrogen removal of the present invention is 7 × 10 ^{8 for} nitrifying bacteria at a fly ash content of 10%,
Denitrifying bacteria were 3 × 10 ⁹ and general bacteria were 5 × 10 ^{9. At} a fly ash content of 20%, nitrifying bacteria were 10 ⁹ , denitrifying bacteria were 8 × 10 ⁹ , and general bacteria were 10 ¹⁰ . As can be seen from this result, by including fly ash, nitrifying bacteria, general bacteria, and the number of both denitrifying bacteria increase,
In particular, it was found that the increase in denitrifying bacteria was remarkable. And the result of FIG. 3 shows the result of the present invention containing fly ash.
The entrapment immobilization carrier for nitrogen removal suggests the possibility of improving the nitrogen removal performance of ammoniacal nitrogen wastewater, especially the performance of denitrification treatment, as compared with the conventional product containing no fly ash.

From the results of this acclimatization test, the present inventors
Iron oxide (content 10%), fly ash (content 5,
10%), the nitrogen of the present invention containing kaolin (20%)
With respect to the entrapping immobilization carrier for removal, a confirmation test of nitrogen removal performance using sewage having an ammonia nitrogen concentration of 20 mg / l was continuously performed for 30 days. As a comparative example, a conventional product to which no metal oxide was added was used. FIG. 4 shows the result.

In FIG. 4, the concentration of ammoniacal nitrogen (NH ₄ —N) in the treated water 30 days after the test was such that the entrapping immobilization carrier for nitrogen removal of the present invention containing a metal oxide also contained a metal oxide. The conventional product which did not have the same value of 2 mg / l or less.

However, nitrite ions (N
The concentration of O ₂ -N) is 5 mg / l or less for the conventional product, 2 mg / l or less for 5% fly ash, and 10% for fly ash, 10% iron oxide and 20% kaolin. Could be reduced to 1 mg / l or less. On the other hand, the concentration of nitrate ion (NO ₃ -N) in the treated water is 18 to 19 mg / l for the conventional product, 14 mg / l or less for 5% fly ash, and 10 mg / l for 10% fly ash. 1 or less, 8% with 10% iron oxide
mg / l or less, and kaolin 20% reduced to 7 mg / l or less.

Thus, the nitrite ion (NO ₂ -N)
As explained in FIG. 3, the cause of the decrease in the density is as follows.
It is considered that the density of the denitrifying bacterium was remarkably increased by the inclusion of the metal oxide, whereby the nitrous acid and nitric acid generated by the nitric acid bacterium were rapidly reduced to nitrogen.

In the above confirmation test, in addition to the nitrogen removal performance, as shown in FIG. 4, the compressive strength, specific gravity, and sedimentation of the entrapping immobilization carrier for nitrogen removal at the start of the test (day 0) and after 30 days from the test Changes in speed were also investigated.

As a result, after 30 days from the test, both the compressive strength and the sedimentation speed of the entrapping immobilization carrier for removing nitrogen of the present invention and the conventional product were smaller than those at the start of the test. However, while some of the conventional products were broken, the nitrogen- immobilized encapsulating immobilization carrier of the present invention has a high compressive strength at the start of the test. Not at all. In addition , the entrapping immobilization carrier for removing nitrogen of the present invention was also improved in fluidity as compared with the conventional product.

As described above, according to the present invention, a nitrifying bacterium,
It is possible to improve the fluidity without adversely affecting the denitrifying bacteria , improve the abrasion resistance, and obtain an entrapping immobilization carrier for nitrogen removal having an enhanced performance of removing nitrogen from wastewater. Furthermore, by including an additive material having a low material cost, the amount of expensive hydrogel can be reduced, so that the cost of the entrapping immobilization carrier for nitrogen removal can be reduced.

[0041]

As described above, according to the present invention, it is possible to remove nitrogen.
According to the leaving entrapping immobilization carrier and the method of forming the same, since the entrapping immobilization carrier for nitrogen removal is formed by adding a metal oxide to the polymer hydrogel, the nitrogen removal performance and abrasion resistance are improved, Can be simultaneously solved by a simple method to improve a plurality of problems of moldability at the time of molding a carrier, and is extremely useful.

Further, since the specific gravity is increased by including the metal oxide, it was possible to take measures against the hanging insect.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a flow illustrating a method for forming an entrapping immobilization carrier for nitrogen removal according to the present invention.

FIG. 2 is a table showing the physical properties of the entrapping immobilization carrier for nitrogen removal of the present invention.

FIG. 3 is a graph showing the relationship between the metal oxide content and the growth rate of nitrifying bacteria, general bacteria, and denitrifying bacteria.

FIG. 4 is a table showing water quality and the like of treated water when ammoniacal nitrogen wastewater is treated using the entrapping immobilization carrier for nitrogen removal of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-257180 (JP, A) JP-A-63-137681 (JP, A) JP-A-2-65782 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C12N 11/00-11/18

Claims (5)

(57) [Claims] 1. A nitrifying bacteria and entrapping immobilization pellets for entrapping immobilization to nitrogen removal activated sludge in the water-containing polymer gel containing denitrifying bacteria and
Thereby forming iron oxide in said water-containing polymer gel, at least one metal oxide powder and nitrogen removal entrapping immobilization pellets, characterized in that it contains selected from silicon oxide. 2. The entrapping immobilization carrier for removing nitrogen according to claim 1, wherein the content of the metal oxide fine powder is 5 to 20% by weight in a state of a hydrogel. 3. The metal oxide fine powder has an average particle size of 5
The nitrogen of claim 1 or 2, wherein
Entrapping immobilization carrier for removal . 4. The entrapping immobilization carrier for nitrogen removal according to claim 2, wherein the metal oxide fine powder is a mixture containing iron oxide and silicon oxide as main components. 5. A mixed liquid obtained by mixing activated sludge containing nitrifying bacteria and denitrifying bacteria and metal oxide fine powder and allowed to stand for 1 to 2 hours is suspended in a gel raw material liquid to prepare a suspension. A method for forming an entrapping immobilization carrier for removing nitrogen , wherein the suspension is gelled.