JPH10180291A - Nitrificating-denitrificating method of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove a nitrogen component in a waste water by executing nitrification.denitrification in one reactor, to make a device remarkably compactor and also to reduce a treating time and a treating cost. SOLUTION: The inside of a reactor 12 is kept in an aerobic state by aerating air into the reactor 12 and regulating an opening degree of an aerating rate regulating valve 42 with a controller 22 so that a DO concn. (dissolved oxygen concn.) in the reactor may be 0.5-5mg/l based on the DO concn. measured with a DO sensor 20. This aerobic state is kept for 10-20min. In this way, ammonia nitrogen in the waste water is aerobically denitrificated by a reaction process of NH4 →NH2 OH→N2 since the aerobic state for executing an aerobic denitrification is formed. Then the aeration into the reactor 12 is stopped with the controller 22 and also the DO concn. in the reactor is kept in <=0.5mg/l to keep the inside of the reactor 12 in an anaerobic state, and this anaerobic state is kept for 15-60min. In this way, a nitrate nitrogen and nitrous nitrogen remained by the aerobic denitrification are anaerobiacally denitrificated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a method for nitrifying and denitrifying wastewater,
In particular, the present invention relates to a wastewater nitrification and denitrification method for biologically removing nitrogen components in wastewater.

[0002]

2. Description of the Related Art In recent years, studies have been made on water pollution control measures on a global environmental scale. One of the development issues of biological wastewater treatment is to improve the efficiency of removing ammonia nitrogen in wastewater. . Conventionally, as a typical example of a nitrification / denitrification method for biologically removing a nitrogen component from wastewater, there is a modified activated sludge circulation method. In this nitrification and denitrification method, ammonia nitrogen in wastewater is first oxidized to nitrite nitrogen or nitrate nitrogen under aerobic conditions by utilizing the ammonia oxidation ability of nitrifying bacteria, which are autotrophic bacteria, in a nitrification tank. After that, in the denitrification tank, anaerobic denitrification in which the nitrite nitrogen and nitrate nitrogen are reduced to nitrogen gas in an anaerobic state using a hydrogen donor such as methanol as a nutrient by the action of a heterotrophic bacterium denitrification bacterium I do. This removes nitrogen from the wastewater.

[0003]

However, the conventional method of nitrifying and denitrifying wastewater involves a nitrification tank (aerobic tank) for working nitrifying bacteria, which is an aerobic bacterium, and a denitrifying bacteria, which is an anaerobic bacterium. Since two denitrification tanks (anaerobic tanks) are required to work, there is a disadvantage that the apparatus becomes large. In addition, since nitrate nitrogen, which is the final oxidation product produced by oxidizing ammonia nitrogen, and then nitrate nitrogen, is reduced to nitrogen gas, processing time is long and it is not efficient. There is.

[0004] Further, since a hydrogen donor, which is a nutrient source of the denitrifying bacteria, such as methanol, is required, there is a disadvantage that the treatment cost is high. In view of such circumstances of the present invention, it is possible to efficiently remove nitrogen components in wastewater by performing nitrification and denitrification treatment in one reaction tank,
The device can be made much more compact,
An object of the present invention is to provide a method for nitrifying and denitrifying wastewater, which can reduce the processing time and the processing cost.

[0005]

In order to achieve the above object, the present invention provides a method of nitrifying and denitrifying wastewater for biologically removing ammonia nitrogen in wastewater, comprising the steps of:
The method is characterized in that nitrifying bacteria, iron oxidizing bacteria, and denitrifying bacteria coexisting in one reaction vessel are brought into contact with each other, and an aerobic state and an anaerobic state are formed at least once in the reaction vessels.

According to the present invention, when the reaction tank is in an aerobic state, nitrifying bacteria and iron-oxidizing bacteria convert ammonia-based nitrogen into aerobic denitrification at the stage of hydroxylamine, an intermediate product of oxidized nitrogen. At the same time, during the anaerobic condition, hydroxylamine remaining without being converted to nitrite nitrogen or nitrate nitrogen is aerobically denitrified. In addition, when the reaction tank is in an anaerobic state, nitrifying bacteria and denitrifying bacteria convert ammonia nitrogen into anaerobic denitrification at the stage of nitrite nitrogen and nitrate nitrogen, the final products of oxidized nitrogen. Along with
In the aerobic state, nitrite nitrogen and nitrate nitrogen converted from hydroxylamine to final oxidation products without aerobic denitrification are anaerobically denitrified.

That is, the processing time is short in the aerobic state,
Aerobic denitrification that does not require a hydrogen donor such as methanol is performed, and nitrite nitrogen and nitrate nitrogen that are not removed by aerobic denitrification are removed by anaerobic denitrification. Can be obtained, and the processing cost and processing time can be reduced. Furthermore, nitrification and denitrification can be performed in one reaction tank.

Further, the aerobic condition is such that the dissolved oxygen concentration is 0.5 to 5 mg / l and the aerobic holding time is 10 to 20 minutes, and the anaerobic condition is that the dissolved oxygen concentration is 0.5 mg / l.
By setting the anaerobic holding time to 15 to 60 minutes below,
Aerobic and anaerobic denitrification can be performed efficiently. Furthermore, by repeating the aerobic state and the anaerobic state a plurality of times, the amount of hydroxylamine generated increases, so that aerobic denitrification, which is advantageous in processing time and processing cost, can be performed in preference to anaerobic denitrification. it can.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for nitrifying and denitrifying wastewater according to the present invention will be described below in detail with reference to the accompanying drawings. Before describing the embodiments of the present invention, the theoretical basis of the present invention will be described first.

[0010] The inventors of the present invention contact the ammonia-containing wastewater under aerobic conditions with a carrier on which a mixed bacterium of nitrifying bacteria and iron oxidizing bacteria is immobilized to thereby obtain (1)
As shown in the equation, before being oxidized to nitrite nitrogen (NO ₂ -N) or nitrate nitrogen (NO ₃ -N) which is a final oxidation product of ammonia nitrogen (NH ₄ -N). It has been found that an aerobic denitrification reaction occurs in the stage of an intermediate product, hydroxylamine (NH ₂ OH), which is oxidized to nitrogen gas (N ₂ ).

NH ₄ → NH ₂ OH → N ₂ (1) That is, nitrifying bacteria oxidize ammoniacal nitrogen to hydroxylamine, and iron oxidizing bacteria oxidize hydroxylamine to nitrogen gas. The reaction takes place.
This aerobic denitrification has a great merit that the treatment time is short and does not require a hydrogen donor such as methanol, but on the other hand, nitrous nitrogen and nitrate nitrogen are not aerobicly denitrified at the hydroxylamine stage. There is a disadvantage that the oxidized nitrogen oxide remains in the treated water.

The present invention has been made based on the above findings, and combines anaerobic denitrification in order to improve the total nitrogen (TN) removal rate while maximizing the advantages of aerobic denitrification. At the same time, the aerobic denitrification and the anaerobic denitrification can be efficiently performed in one reaction tank. FIGS. 1 to 4 show a dissolved oxygen concentration (hereinafter referred to as a DO concentration) and an aerobic concentration suitable for performing aerobic denitrification in a state where nitrifying bacteria, iron oxidizing bacteria, and denitrifying bacteria coexist in a reaction tank. It is the figure which investigated the retention time, the dissolved oxygen concentration (henceforth DO concentration) suitable for performing anaerobic denitrification, and the anaerobic retention time.

FIG. 1 shows the relationship between the DO concentration and the nitrogen removal rate under aerobic conditions. As shown in FIG.
When the O concentration is 0.5 mg / l or less and 5 mg / l or more, the nitrogen removal rate decreases. This is because if the DO concentration is too low, the activity of nitrifying bacteria and iron-oxidizing bacteria becomes too small and aerobic denitrification is hardly performed, while if the DO concentration is too high, the activity of nitrifying bacteria becomes too large and hydroxylamine It is considered that the rate of conversion from nitrogen to nitrite nitrogen or nitrate nitrogen increases. Therefore, the DO concentration condition for performing aerobic denitrification is preferably 0.5 to 5 mg / l.

FIG. 2 shows the relationship between the aerobic holding time and the nitrogen removal rate when the DO concentration is 0.5 to 5 mg / l. FIG. 2 shows a DO concentration appropriate for aerobic denitrification in which the time factor is added to the results of FIG. As shown in FIG. 2, when the aerobic holding time is 10 minutes or less and 20 minutes or more, the nitrogen removal rate decreases. Therefore, the aerobic holding time for performing aerobic denitrification is preferably 10 to 20 minutes.

From FIGS. 1 and 2, in order to efficiently perform aerobic denitrification, it is preferable that the DO concentration is 0.5 to 5 mg / l and the aerobic holding time is 10 to 20 minutes. FIG. 3 shows the relationship between the DO concentration and the nitrogen removal rate under anaerobic conditions. As shown in FIG. 3, when the DO concentration is 0.5 mg / l or more, the nitrogen removal rate decreases. This means that the DO concentration is 0.
It is considered that in the aerobic state of 5 mg / l or more, even if the nitrification reaction is performed by the nitrifying bacteria, the activity of the denitrifying bacteria becomes too small and the anaerobic denitrification becomes slow. In the anaerobic state where the DO concentration is 0.5 mg / l or less, the activity of the nitrifying bacteria decreases and the nitrification reaction becomes slow, but the activity of the denitrifying bacteria increases. It is considered that nitrate nitrogen is surely anaerobically denitrified. FIG. 4 shows the results of FIG. 3 in which a time factor is added to determine the DO concentration appropriate for anaerobic denitrification. As shown in FIG. 4, when the anaerobic holding time is 15 minutes or less and 60 minutes or more, the nitrogen removal rate decreases. Therefore, the anaerobic holding time for performing anaerobic denitrification is preferably 15 to 60 minutes.

From FIGS. 3 and 4, in order to efficiently perform anaerobic denitrification, it is preferable that the DO concentration is 0.5 mg / l or less and the aerobic holding time is 15 to 60 minutes. FIG. 5 is a cross-sectional view showing an example of a nitrification / denitrification apparatus to which the method for nitrification / denitrification of wastewater of the present invention is applied. The nitrification / denitrification apparatus 10 mainly includes a reaction tank 12 in which nitrifying bacteria, iron oxidizing bacteria, and denitrifying bacteria are stored in a mixed state, and a raw water supply pipe for supplying wastewater to an air reservoir described later in the reaction tank 12. 14 and the reaction tank 12
An aerator 16 for aerating air into the inside, a stirrer 18 for slowly stirring the wastewater in the reaction tank 12, a DO sensor 20 for measuring the DO concentration of the wastewater in the reaction tank 12, and a measured value from the DO sensor 20 Controller 2 that controls the driving of the aerator 16 and the amount of aeration and the driving of the stirrer 18 based on the
2 and a treated water pipe 24.

For the nitrifying bacteria, iron oxidizing bacteria, and denitrifying bacteria contained in the reaction tank 12, use of an entrapping immobilization carrier entrapped and immobilized on an immobilizing material can increase the number of bacteria in the reaction tank 12. It is preferable to keep the concentration. In FIG. 5, an entrapping immobilization carrier A in which nitrifying bacteria and denitrifying bacteria are mixed and an entrapping immobilization carrier B in which iron-oxidizing bacteria are entrapped and immobilized were used. As a material for immobilizing the carrier to be comprehensively immobilized, a polymer gel obtained by gelling polyethylene glycol, polyvinyl alcohol, acrylamide, polyvinyl formal, or the like can be used. In the lower part of the reaction tank 12, a wire mesh diffusion plate 2 is provided.
6 is disposed in the lateral direction of the reaction tank 12, a reaction section 28 in which the entrapping immobilization carrier is accommodated is formed above the diffusion plate 26, and air from the aeration device 16 is blown below the diffusion plate 26. An air storage section 30 for storing is formed. Thus, the air aerated in the air reservoir 30 is uniformly supplied to the entire reaction unit 28 by the diffusion plate 26. Further, a screen 32 for preventing carrier outflow is provided in the treated water discharge part 31 at the upper part of the reaction tank 12.

The aeration device 16 includes an air diffuser 36 disposed in the air reservoir 30, a blower 38 for supplying compressed air to the air diffuser 36, an air pipe 40 connecting the blower 38 and the air diffuser 36, and an air pipe. And an aeration amount adjusting valve 42 provided in the middle of 40. The controller 22 is a DO
The aeration amount is controlled by adjusting the opening of the aeration amount adjustment valve 42 based on the DO concentration in the reaction tank 12 measured by the sensor 20, and a timer set in advance by a timer mechanism built in the controller 22. The opening / closing time of the aeration amount adjusting valve 42 is controlled based on the air holding time and the anaerobic holding time. Further, the agitator 18 is operated when the aeration amount adjusting valve 42 is closed.

Next, a nitrification / denitrification apparatus configured as described above.
The method for nitrification and denitrification of wastewater of the present invention will be described below. Con
The trawler 22 opens the aeration amount adjusting valve 42 to open the reaction tank.
Aerating air inside 12 and measuring with DO sensor 20
D in the reaction tank based on the measured DO concentration in the reaction tank 12
Adjust the aeration amount so that the O concentration becomes 0.5 to 5 mg / l.
The opening of the lube 42 is adjusted to bring the inside of the reaction tank 12 into an aerobic state.
I do. And, by the timer mechanism of the controller 22,
Maintain an aerobic state for 10-20 minutes. This makes it
An aerobic condition is formed to efficiently perform denitrification
And the ammonia nitrogen in the wastewater is NH_Four→ NH_TwoOH
→ N_TwoAerobic denitrification by the reaction path of Next, aerobic
If the state continues for 10 to 20 minutes, the controller 22
Closes the aeration amount adjustment valve 42 and exposes the inside of the reaction tank 12.
And the reaction measured by the DO sensor 20
DO concentration in reaction tank 12 based on DO concentration in tank 12
The stirrer slowly so that the
Rotate to degas air in wastewater and anaerobic inside reaction tank 12
State. And a timer mechanism of the controller 22
Maintain this anaerobic state for 15-60 minutes. this
Gives NH_Four→ NO_Three-N (NO _Two-N) → N_TwoAnti
Anaerobic denitrification by response route. Therefore, survived by aerobic denitrification
Nitrate nitrogen and nitrite nitrogen are removed.

As a result, the total nitrogen (TN) removal rate can be improved while maximizing the advantages of aerobic denitrification. Further, since aerobic denitrification and anaerobic denitrification can be efficiently performed in one reaction tank 12, it is necessary to form an aerobic tank and an anaerobic condition for forming aerobic conditions as in the related art. It does not require two anaerobic tanks. Therefore, nitrification
It is possible to greatly reduce the size of the denitrification device.

In this case, by repeatedly forming the aerobic state and the anaerobic state a plurality of times, the amount of hydroxylamine produced increases, so that the efficiency of aerobic denitrification can be further improved. Therefore, the advantage of aerobic denitrification can be further utilized. In the present embodiment, the aerobic state is first formed in the reaction tank, and then the anaerobic state is formed. However, the aerobic state is formed after the reaction tank is first set in the anaerobic state. You may. In this case, hydroxylamine remaining in anaerobic denitrification is removed by aerobic denitrification.

[0022]

【Example】

(Embodiment 1) An embodiment performed using a nitrification / denitrification apparatus as shown in FIG. 5 will be described. In the reaction tank, a first carrier entrapping and immobilizing nitrifying bacteria and denitrifying bacteria in a mixed state and a second carrier entrapping and immobilizing iron-oxidizing bacteria were accommodated. As the first carrier, standard activated sludge from a sewage treatment plant was used as an inoculum for immobilization. Comprehensive fixation: activated sludge 2% by weight, polyethylene glycol prepolymer 15% by weight,
The reaction was carried out by mixing 0.5% by weight of N, N, N ', N'-tetramethylethylenediamine and 0.25% by weight of potassium persulfate in water to form a gel. The obtained gel was cut into 3 mm square die-shaped pellets (carriers). Then, the obtained pellet was cultured in wastewater having an ammonia nitrogen concentration of 30 mg / l. The culture conditions were as follows: pellet filling rate 10%, DO concentration in wastewater 4.5 to 6
Performed at mg / l. The number of nitrifying bacteria in the pellet on day 90 of the culture was 2.0 × 10 ¹⁰ cells / pellet.
/ Cm ³ , and the number of denitrifying bacteria was 4.57 × 10 ⁹ cells / cm ³ per pellet. The pellets of the cultured nitrifying and denitrifying bacteria were charged into the reaction tank so as to have a filling rate of 15%.

On the other hand, as for iron oxidizing bacteria, a sample collected from a waste mine was entrapped and immobilized in the same manner as nitrifying bacteria. Then, the obtained pellets have an ammonia nitrogen concentration of 30 mg.
Per liter and 30 mg / l of divalent iron in wastewater. The culture conditions were as follows: pellet filling rate 10%, D in wastewater.
The test was performed at an O concentration of 4.5 to 6 mg / l. The number of iron oxidizing bacteria in the pellet on day 90 of the culture was 3.
It was 25 × 10 ⁹ cells / cm ³ . The cultured pellets of iron oxidizing bacteria were charged into the reaction tank so as to have a filling rate of 3%.

The concentration of ammonia nitrogen in the wastewater subjected to the test was 30 mg / l, and the hydrogen donor as a nutrient source of the denitrifying bacteria was sodium acetate (C) having a C / N ratio of 1.
6 was added. The residence time in the reactor was 3 hours. The aerobic holding time for maintaining the DO concentration at 0.5 to 5 mg / l was 15 minutes, and the DO concentration was 0.5 mg / l.
The anaerobic holding time maintained below was 45 minutes.

As a comparative example, the experiment was performed under the same conditions as in the example except that no iron-oxidizing bacteria were present in the reaction tank. As a result, the quality of the treated water of the comparative example was found to be NH ₄ —N concentration 11 mg / l.
Hereinafter, the NH ₂ OH concentration is 13 mg / l or less, the NO ₂ -N concentration is 0.1 mg / l or less, the NO ₃ -N concentration is 0.1 mg / l or less, and the total nitrogen concentration is about 24 mg / l. 20
% Was bad.

On the other hand, the quality of the treated water of the embodiment is N
H ₄ -N concentration 5 mg / l or less, NH ₂ OH concentration 0.1 mg / l
Hereinafter, the NO ₂ -N concentration was 0.1 mg / l or less, the NO ₃ -N concentration was 0.1 mg / l or less, and the total nitrogen concentration was 5 mg / l or less, and the nitrogen removal rate was 83% or more. A large amount of hydroxylamine (NH ₂ OH) remains in the treated water of the comparative example, and it can be seen that aerobic denitrification in the presence of iron oxidizing bacteria is effective for removing total nitrogen in the treated water. . Therefore, it was confirmed that even if the inside of the reaction tank was first made anaerobic, then an aerobic state was formed, and the remaining hydroxylamine by anaerobic denitrification was removed by aerobic denitrification, and it was sufficiently effective.

[0027]

As described above, according to the method for nitrifying and denitrifying wastewater of the present invention, while maximizing the advantages of aerobic denitrification, the nitrite nitrogen remaining in aerobic denitrification can be reduced. Nitrate nitrogen can be removed by anaerobic denitrification. As a result, the total nitrogen removal rate can be improved, and the processing time and processing cost can be reduced by performing aerobic denitrification.

Further, since the aerobic denitrification and the anaerobic denitrification can be efficiently performed in one reaction tank, the aerobic tank and the anaerobic condition for forming the aerobic condition are used. It does not require two anaerobic tanks to form. Therefore, the size of the apparatus can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the relationship between dissolved oxygen concentration and nitrogen removal rate under aerobic conditions.

FIG. 2 is an explanatory diagram showing the relationship between aerobic holding time and nitrogen removal rate under aerobic conditions.

FIG. 3 is an explanatory diagram showing a relationship between a dissolved oxygen concentration and a nitrogen removal rate under anaerobic conditions.

FIG. 4 is an explanatory diagram showing the relationship between aerobic holding time and nitrogen removal rate under anaerobic conditions.

FIG. 5 is a cross-sectional view illustrating a nitrification / denitrification apparatus to which the wastewater nitrification / denitrification method of the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Nitrification / denitrification apparatus 12 ... Reaction tank 14 ... Raw water supply pipe 16 ... Aeration device 18 ... Stirrer 20 ... DO sensor 22 ... Controller 26 ... Diffusion plate 28 ... Reaction part 30 ... Air reservoir part 32 ... Screen 42 ... Aeration amount Adjustment valve

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takako Ogasawara 1-1-1 Uchikanda, Chiyoda-ku, Tokyo Inside Hitachi Plant Construction Co., Ltd.

Claims (4)

[Claims] 1. A method of nitrifying and denitrifying wastewater for biologically removing ammonia nitrogen in wastewater, wherein the nitrifying bacteria, iron oxidizing bacteria, and denitrifying bacteria coexist in the wastewater and one reaction tank. And nitrifying and denitrifying wastewater, wherein an aerobic state and an anaerobic state are formed at least once in the reaction tank. 2. The method for nitrifying and denitrifying wastewater according to claim 1, wherein an aerobic state is formed first in said reaction tank and then an anaerobic state is formed. 3. The aerobic condition, wherein the dissolved oxygen concentration is 0.5
The aerobic holding time is 10 to 20 minutes at 〜5 mg / l, and the anaerobic state is that the dissolved oxygen concentration is 0.5 mg / l or less and the anaerobic holding time is 15 to 60 minutes. Item 10. The method for nitrifying and denitrifying wastewater according to item 1 or 2. 4. The nitrifying bacteria, iron oxidizing bacteria, and denitrifying bacteria,
4. The method for nitrifying and denitrifying wastewater according to claim 1, wherein the carrier is a carrier entrapped and fixed in a polymer gel.