JP2000061494A - Biological treatment of ammonia nitrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and effectively perform nitrification reaction of nitrous acid type by biologically treating ammonia nitrogen. SOLUTION: A biological reactor 14 is constituted of a nitrification tank consisting of two tanks a first stage nitrification tank 24 and a second stage nitrification tank 26, a denitrification tank consisting of two tanks, a first stage denitrification tank 28 and a second denitrification tank 30, and one aerobic tank 32. In this way, the load quantity of ammonia nitrogen per the first stage nitrification tank 24 is kept at 1.5-2.5 kg-N/m3.day, and the concentration of ammonia nitrogen in the first stage nitrification tank 24 is kept at 250-550 mg/L, thereby enabling to dominantly perform nitrification reaction of nitrous acid type be stopping nitrification reaction in the stage of nitrous acid nitrogen which is an intermediate product for oxidizing ammonia nitrogen to nitric acid nitrogen. Therefore, since the nitrification reaction of nitrous acid type can be stably performed, the time required for the nitrification reaction can be shortened, and also the aeration quantity of air for forming aerobic conditions can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biologically treating ammoniacal nitrogen, and more particularly to a method for biologically removing high concentrations of ammoniacal nitrogen.

[0002]

2. Description of the Related Art Ammonia nitrogen contained in wastewater such as sewage, night soil, industrial wastewater, etc. is said to be a cause of declining dissolved oxygen and eutrophication in closed water bodies such as lakes and inner bays. . Conventionally, as a nitrogen removal technology for removing nitrogen components from these wastewaters, biological nitrification / denitrification treatment using microorganisms has been performed. Biological nitrification and denitrification treatment utilizes the ammonia oxidizing power and nitrite oxidizing power of autotrophic nitrifying bacteria to remove ammoniacal nitrogen in wastewater in an aerobic state through nitrite nitrogen and nitrate. Oxidize to neutral nitrogen. Then, by the action of denitrifying bacteria, which are heterotrophic bacteria, the organic matter in the wastewater is used as an electron donor to reduce nitrate nitrogen to nitrogen gas in an anaerobic state, thereby removing the ammoniacal nitrogen in the wastewater.

Therefore, the nitrification reaction is carried out in two steps, as shown in the following equation, a reaction of oxidizing ammonia to nitrite nitrogen and a reaction of oxidizing nitrite nitrogen to nitrate nitrogen. NH ₄ -N → NO ₂ -N → NO ₃ -N In addition, the denitrifying bacteria in the denitrification treatment after the nitrification reaction are:
It is possible to reduce nitrite nitrogen to nitrogen gas.

By the way, if the nitrification reaction can be carried out at a stage of nitrous acid, which is an intermediate product for oxidizing ammonia nitrogen to nitric acid, the nitrification type nitrification reaction that stops the nitrification reaction can be carried out, air is supplied during the nitrification reaction. The amount of aeration can be reduced,
The operating power cost of the blower can be significantly reduced.
Further, the amount of organic substances such as methanol, which is a nutrient source in the denitrification process, can be reduced. Furthermore, since it is not necessary to react up to nitrate nitrogen, the time required for the nitrification reaction can be shortened.

From such a background, conventionally, the dissolved oxygen of the liquid in the nitrification tank is changed, the pH is controlled, or a method for inhibiting microorganisms by using organic ammonia or nitrous acid is used. Then, an attempt has been made to carry out a nitrite type nitrification reaction.

[0006]

However, in any of the above-mentioned conventional attempts, a nitrite type nitrification reaction that stops the nitrification reaction at the stage of nitrite which is an intermediate product that oxidizes ammoniacal nitrogen to nitric acid is carried out. Could not be done. The present invention has been made in view of such circumstances, and an object thereof is to provide a biological treatment method of ammoniacal nitrogen capable of stably and efficiently performing a nitrite type nitrification reaction. To do.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method of contacting wastewater containing ammoniacal nitrogen with a microorganism-immobilized carrier under aerobic conditions in a nitrification tank. In the biological treatment method of ammoniacal nitrogen for nitrifying nitrogen, the ammoniacal nitrogen load per nitrification tank is 1.5 to 2.5 kg-N / N.
The nitrite type nitrification reaction is carried out by maintaining m ³ · day and maintaining the concentration of ammonia nitrogen in the nitrification tank at 250 to 550 mg / L.

According to the present invention, the ammonia nitrogen load per nitrification tank is maintained at 1.5 to 2.5 kg-N / m ³ · day, and the ammonia nitrogen concentration in the nitrification tank is set to 250.
Since it is maintained at ˜550 mg / L, the nitrite type nitrification reaction can be carried out stably and efficiently.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the biological treatment method for ammoniacal nitrogen according to the present invention will be described below in detail with reference to the accompanying drawings. The rationale for the ammoniacal nitrogen biological treatment method of the present invention will be described. The inventors have established a management index for stably and efficiently performing a nitrite type nitrification reaction that stops the nitrification reaction at the stage of nitrite nitrogen, which is an intermediate product that oxidizes ammoniacal nitrogen to nitrate nitrogen. It was investigated.

(1) First, the relationship between the nitrite type nitrification reaction and the amount of ammonia nitrogen loaded per nitrification tank will be described. FIG. 1 shows the relationship between the amount of ammonia nitrogen loading per nitrification tank (hereinafter referred to as “load”) and the nitrite type nitrification reaction. That is, only 1000 (mg of ammoniacal nitrogen (NH ₄ -N) is contained in a nitrification tank containing a microorganism-immobilized carrier (hereinafter referred to as “carrier”) having a filling rate of 20%.
/ L) was supplied, and the nitrification reaction was performed while increasing the load amount to 0.8 to 3.0 (kg-N / m ³ · day). Then, the ammoniacal nitrogen concentration (NH ₄ -N), the nitrite nitrogen concentration (NO ₂ -N), and the nitrate nitrogen concentration (NO _3- ) in the nitrification liquid in the nitrification tank at this time.
The change in N) was examined.

FIG. 2 shows the ratio of nitrite nitrogen to the total amount of nitrate nitrogen and nitrite nitrogen when the load is increased based on the data of FIG. 1 (hereinafter referred to as “nitrite ratio”). )
Is shown. In FIG. 2, a ratio of 1 means that a complete nitrite type nitrification reaction is performed, and a ratio of 0 means that a complete nitric acid type nitrification reaction is performed.

As can be seen from FIGS. 1 and 2, when the load was 0.8 (kg-N / m ³ · day), only nitrate nitrogen was found in the nitrification solution in the nitrification tank. . This means that when the load is 0.8 (kg-N / m ³ · day), the nitric acid type nitrification reaction, in which all of the ammoniacal nitrogen is oxidized to nitric acid nitrogen, is completely controlled by the nitrification reaction. Means

When the loading amount is increased to 1.0 (kg-N / m ³ · day), nitrite nitrogen starts to be recognized in the nitrification solution, while the nitrate nitrogen concentration decreases. Then, when the load was 1.1 (kg-N / m ³ · day), the nitrite ratio became about 0.5, and the nitric acid type nitrification reaction and the nitrite type nitrification reaction were in a substantially equilibrium state. Furthermore, the load amount is 1.5 (kg-
(N / m ³ · day), the nitrite ratio became 0.8 and the nitric acid type nitrification reaction became dominant from the nitric acid type nitrification reaction.

When the load amount is around 2.0 (kg-N / m ³ · day), the nitrite ratio reaches a maximum of 0.9 or more, and when the load amount is continuously increased, the nitrite ratio begins to decrease, and When the amount was 2.5 (kg-N / m ³ · day), the nitrite ratio was 0.8. Then, the load amount 3.0 (kg-N /
m ³ · day), the nitrite ratio decreases to about 0.4,
The nitric acid-type nitrification reaction came to dominate again.

In the above case, the load amount is 0.8 (k
g-N / m³・ Day to 3.0 (kg-N / m)³·Day)
However, on the contrary, 3.0 (kg-N
/ M ³・ Day) to 0.8 (kg-N / m)³・ Day)
Similar results were obtained when the above was used. Nitrite type glass mentioned above
Reaction and the amount of ammonia nitrogen loading per nitrification tank
From the relationship, the load amount is 1.5 to 2.5 (kg-N / m³・
(Day) to maintain the nitrite ratio below 0.8.
Dominates the nitrite type nitrification reaction because it can be on top
Can be done on a regular basis.

However, looking at the relationship between the load and the concentration of ammonia nitrogen remaining in the nitrification solution from FIG.
When increasing the load amount, the load amount becomes 1.0 (kg-
(N / m ³ · day), ammoniacal nitrogen started to remain, and thereafter, the residual concentration became higher as the load amount increased. Then, the load amount is 1.5 to 2.5 (kg-N / m ³
・ Residual concentration of ammonia nitrogen in the range of (day) is 2
The range was from 00 to 450 (mg / L). As described above, when the synthetic wastewater having an ammoniacal nitrogen concentration of 1000 (mg / L) is nitrified, the load amount is 1.5 to 2.5 (k
Although the nitrite type nitrification reaction can be predominantly carried out by maintaining it within the range of g-N / m ³ · day), a large amount of ammoniacal nitrogen in which the nitrification reaction does not proceed remains in the nitrification solution. become.

This simply controls the amount of load.
Then there is a problem. (2) Then, the present inventors set the load amount to 1.5 to 2.5.
(Kg-N / m³・ Synthesis in the range of (day)
Ammonia nitrogen concentration in wastewater (hereinafter “wastewater NH _Four-N
Of the ammoniacal nitrogen remaining in the nitrification solution.
Concentration (hereinafter “Nitrification liquid NH_Four-N concentration ")
There were examined.

FIG. 3 shows that the NH ₄ -N concentration of the wastewater is 1000 (m
(g / L) to 100 (mg / L), the nitrification solution NH ₄ -N against the wastewater NH ₄ -N concentration
The residual NH ₄ —N ratio, which is the ratio of the concentrations, was investigated. As can be seen from FIG. 3, the NH ₄ -N concentration of the wastewater is 100%.
The residual NH ₄ -N ratio decreases with decreasing 0 (mg / L) to 100 (mg / L), and the wastewater NH
_{In the 4-} N concentration range of 550 to 250 (mg / L), the residual NH _4- N ratio was the minimum region of 0.1 or less. Then, when the NH ₄ -N concentration of the wastewater fell below 250 (mg / L), the residual NH ₄ -N ratio increased again.

From the results of (1) and (2) above, the inventors have found that the load amount is 1.5 to 2.5 (kg-N / m ³ · day).
And maintain the ammonia nitrogen concentration of wastewater at 2
It was found that the nitrite type nitrification reaction can be stably and efficiently carried out by maintaining the range of 50 to 550 (mg / L). By the way, the nitrifying bacteria that carry out the nitrification reaction are roughly classified into AH bacteria that exhibit high activity under conditions of high-concentration ammoniacal nitrogen atmosphere and AL that exhibits high activity under conditions of low-concentration ammoniacal nitrogen atmosphere. There are fungi. And, AH bacteria has an ammoniacal nitrogen concentration of 4
It proliferates preferentially in the area of 00 (mg / L) or more, the number of bacteria is remarkably increased, and the nitrification rate is remarkably increased. In contrast, the AL bacterium has an ammoniacal nitrogen concentration of 200 (mg /
L) and the following regions are preferentially propagated, marked growth of the number of bacteria is observed, and the nitrification rate shows a parabola with a peak at 100 (mg / L). Moreover, the ammonia nitrogen concentration is 150 to 40.
In the region of 0 (mg / L), AH bacteria and AL bacteria propagate in a mixed phase, and the nitrification rate produces a synergistic effect due to the mixing of two kinds of bacteria.

Therefore, the ammonia nitrogen concentration is 250
To 550 (mg / L), 400 to 550
When maintaining in the range of (mg / L), it is preferable to use a microorganism-immobilized carrier in which AH bacteria are preferentially propagated in advance. Here, the AH bacterium is a concentration of 5000 (mg / L)
Refers to nitrifying bacteria that are detected by culturing for 8 weeks in an ammonium sulfate solution, and AL bacterium refers to nitrifying bacteria that are detected by culturing for 8 weeks in an ammonium sulfate solution with a concentration of 100 (mg / L).

The present invention is based on the above findings, and an ammoniacal nitrogen treatment for nitrifying ammoniacal nitrogen is carried out by bringing wastewater containing ammoniacal nitrogen into contact with a microorganism-immobilized carrier under aerobic conditions in a nitrification tank. In the biological treatment method of nitrogen, the ammonia nitrogen loading per nitrification tank is maintained at 1.5 to 2.5 kg-N / m ³ · day, and the ammonia nitrogen concentration in the nitrification tank is 250 to 550 mg. / L
It is configured to maintain.

FIG. 4 shows an example of an apparatus 10 to which the method for biological treatment of ammonia nitrogen according to the present invention is applied. As shown in FIG. 4, a water pipe 18 is connected in the middle of a raw water pipe 16 connecting the raw water tank 12 and the bioreactor 14, and the raw water pipe 16 and the water pipe 18 are provided with flow rate adjusting pumps 20 and 22, respectively. It is arranged. Thereby, the waste water supplied from the raw water tank 12 to the bioreactor 14 can be diluted with tap water.

The bioreactor 14 is constructed by alternately arranging a plurality of nitrification tanks and denitrification tanks in series, and arranging an aerobic tank at the final stage. In FIG. 4, the first-stage nitrification tank 24 is shown. And a second-stage nitrification tank 26, which is a nitrification tank, a second-stage denitrification tank 28 and a second-stage denitrification tank 30, and a single aerobic tank 32.
An example is shown below. In each of the nitrification tanks 24 and 26, in addition to suspended sludge, a large number of carriers 34 in which nitrifying bacteria are entrapped and immobilized,
34 ... is stored. Further, diffuser plates 36, 36 are provided at the bottoms of the nitrification tanks 24, 26 and the aerobic tank 32, respectively.
Are arranged, and compressed air is supplied through the air pipe 38. Thereby, each nitrification tank 24, 26 and aerobic tank 32
Air is aerated from the diffuser plate 36 to form an aerobic condition. Screens 40, 40 for preventing carrier outflow are provided at outlets of the nitrification liquid discharged from the nitrification tanks 24, 26 to the denitrification tanks 28, 30, respectively. In addition, each nitrification tank 2
An alkali tank 42 for storing an alkaline liquid such as caustic soda is provided in the vicinity of Nos. 4 and 26, and the alkali tank 42 and each nitrification tank 24, 26 are connected via a pipe 44 and a flow rate adjusting pump 46. As a result, the nitrification tank 2
The pH of the liquid supplied to Nos. 4 and 26 is adjusted.

Floating sludge is suspended in the denitrification tanks 28 and 30, and a stirrer 48 is provided at the bottom of the denitrification tanks 28 and 30.
48 is provided. As a result, the denitrification tank 2 can be
Anaerobic conditions are formed in the denitrification tanks 28 and 30 by slowly stirring the liquid in the tanks 8 and 30. Under this anaerobic condition, the nitrification liquid is denitrified by the denitrifying bacteria contained in the floating sludge to become nitrogen gas. Further, in the vicinity of the denitrification tanks 28 and 30, an organic matter tank 50 for storing organic matter such as methanol, which is a nutrient source for denitrifying bacteria, and an acid solution tank 52 for storing acid solution such as sulfuric acid are provided. The tank 50 and the acid solution tank 52 are connected to the denitrification tanks 28 and 30 via pipes 54 and 56 and flow rate adjusting pumps 58 and 60, respectively. Then, from the nitrification tanks 24, 26 to the denitrification tanks 28, 30.
When the organic matter in the nitrification solution sent to the plant is insufficient, the denitrification tank is supplemented with the organic matter from the organic matter tank 50, and
The pH in the denitrification tanks 28 and 30 is adjusted by the acid solution from the acid solution tank 52.

In the aerobic tank 32, the second-stage denitrification tank 30
When the liquid treated in step 1 comes into contact with the floating sludge under aerobic conditions, a small amount of residual ammoniacal nitrogen and residual organic matter are decomposed. Further, the aerobic tank 32 is provided with a withdrawal pipe 64 and an withdrawal pump 66, and by appropriately withdrawing the liquid from the aerobic tank 32 to adjust the load of the entire bioreactor 14, the wastewater to the bioreactor 14 The load amount per first nitrification tank is controlled together with the supply amount.

A settling tank 62 for settling suspended sludge is provided at the subsequent stage of the bioreactor 14, and sludge settling in the settling tank 62 is returned to the first stage denitrification tank 28 by a return pipe 68 and a return sludge pump 70. It Next, the operation of the biological treatment device configured as described above will be described. When the wastewater in the raw water tank 12 has a high concentration of ammonia nitrogen of about 1000 (mg / L), for example, tap water in the middle of the raw water pipe 16 causes the ammonia nitrogen in the range of 250 to 550 (mg / L). It is diluted to the concentration. Further, the first stage nitrification tank 24 is controlled by the flow rate adjusting pumps 20 and 22.
The amount of wastewater supplied to the aerobic tank 32 is adjusted and the liquid in the aerobic tank 32 is extracted by the extraction pump 66. As a result, the ammonia nitrogen load per first stage nitrification tank 24 is maintained at 1.5 to 2.5 kg-N / m ³ · day.

As described above, the amount of ammonia nitrogen loading per first stage nitrification tank 24 is 1.5 to 2.5 kg-N / m ³
-Nitrite, which is an intermediate product that oxidizes ammoniacal nitrogen to nitrate nitrogen, was maintained on a daily basis and the ammoniacal nitrogen concentration in the first stage nitrification tank 24 was maintained at 250 to 550 mg / L. It is possible to predominantly perform a nitrite type nitrification reaction that terminates the nitrification reaction at the stage of neutral nitrogen. Therefore, the time required for the nitrification reaction can be shortened, and the aeration amount of air for forming the aerobic condition can be reduced.

Next, the nitrification liquid is sent from the first-stage nitrification tank 24 to the first-stage denitrification tank 28 to perform denitrification treatment. In this denitrification process, most of the nitrification solution contains nitrite nitrogen, so that the amount of organic substances used as a nutrient source for denitrifying bacteria can be reduced. The reduction amount of this organic substance will be described with an example using methanol. And are the denitrification reaction formulas of nitric acid type and nitrite type, and Table 1 shows the theoretical value of the ratio of the required amount of methanol to the denitrification amount (methanol / N ratio). [Nitrate type] _{2NO 3 -N +5/3 CH 3 OH →} N 2 + 2OH - +5/3 CO 2 +7/3 H 2 O ... [nitrite type] _{2NO 2 -N + CH 3 OH →} N 2 + 2OH - + CO ₂ + H ₂ O…

[0029]

[Table 1] As can be seen from Table 1, the nitrite type nitrification reaction can reduce the amount of methanol used by 30% as compared with the nitric acid type nitrification reaction.

Next, the liquid in the first denitrification tank 28 is sent to the second nitrification tank 26. In the second stage nitrification tank 26, the low-concentration ammoniacal nitrogen remaining in the first stage nitrification tank 24 is nitrified by a nitrification type nitrification reaction. The nitrification solution nitrified in the second-stage nitrification tank 26 is sent to the second-stage denitrification tank 30 for denitrification treatment, and then finally nitrification treatment is carried out in the aerobic tank 32 to decompose the residual organic matter. It

[0031]

As described above, according to the biological treatment method for ammoniacal nitrogen of the present invention, the nitrite type nitrification reaction can be carried out stably and efficiently. Therefore,
The amount of aeration that is aerated during the nitrification reaction can be reduced, and the operating power cost of the blower can be significantly reduced. Further, the amount of organic substances such as methanol, which is a nutrient source in the denitrification process, can be reduced. Furthermore, since it is not necessary to react up to nitrate nitrogen, the time required for the nitrification reaction can be shortened.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between ammonia nitrogen loading per nitrification tank and nitrite type nitrification reaction.

FIG. 2 shows the ratio of nitrite nitrogen to the total of nitrate nitrogen and nitrite nitrogen (hereinafter referred to as “nitrite ratio”) when the load is increased based on the data of FIG. 1. Graph

FIG. 3 shows the relationship between the concentration of ammonia nitrogen in the synthetic wastewater and the concentration of ammonia nitrogen remaining in the nitrification solution, while maintaining the range of 1.5 to 2.5 (kg-N / m ³ · day). Graph showing

FIG. 4 is a configuration diagram showing a configuration example of an apparatus to which the biological treatment method for ammoniacal nitrogen of the present invention is applied.

[Explanation of symbols]

10 ... Biological processing device 12 ... Raw water tank 14 ... Bioreactor 16 ... Raw water piping 18 ... Water pipe 24 ... 1st stage nitrification tank 26 ... Second stage nitrification tank 28 ... 1st stage denitrification tank 30 ... 2nd stage denitrification tank 32 ... aerobic tank 34 ... Carrier for immobilizing microorganisms 36 ... Air diffuser 38 ... Air piping 40 ... Screen 62 ... Settling tank 68 ... Return sludge piping

Claims (3)

[Claims] 1. A biological treatment method of ammonia nitrogen, comprising nitrifying ammonia nitrogen by contacting wastewater containing ammonia nitrogen with a microorganism-immobilized carrier in a nitrification tank under aerobic conditions. The ammonia nitrogen load per nitrification tank is 1.5 to
Ammonia characterized by carrying out a nitrite type nitrification reaction by maintaining the concentration of ammonia nitrogen in the nitrification tank at 250 to 550 mg / L, while maintaining 2.5 kg-N / m ³ · day. Of biological nitrogen treatment. 2. The ammoniacal nitrogen concentration is set to 400 to 55.
The biological treatment method for ammoniacal nitrogen according to claim 1, wherein a microorganism-immobilized carrier in which AH bacteria, which are nitrifying bacteria, are preferentially propagated is used to maintain the amount at 0 mg / L. 3. The ratio of nitrite nitrogen to the total of nitrate nitrogen and nitrite nitrogen in the nitrification solution becomes 0.8 or more by the nitrite type nitrification reaction. Biological treatment of ammoniacal nitrogen.