JPH10180292A - Method of removing nitrogen from waste water and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of nitrous oxide and to rapidly remove generated nitrous oxide by bringing ammonia-containing waste liquid into contact with nitrifica tion bacteria under an aerobic condition to be performed a nitrification treatment, and then bringing the resultant nitrification liquid into contact with nitrous oxide decomposition bacteria under an anaerobic condition. SOLUTION: The ammonia-containing waste water flowed in a nitrification tank 12 comes into contact with the nitrification bacteria at an aerobic condition to be performed a nitrification treatment, and the nitrification liquid flows out from an outflow part 20 into a nitrous oxide decomposition tank 14. In the nitrous oxide decomposition tank 14, floating sludge containing the nitrous oxide decomposition bacteria is housed and also air in the liquid is deaerated by stirring the liquid with an underwater agitator 24 provided at the bottom, thus the nitrification liquid comes into contact with the nitrous oxide decomposition bacteria under an anaerobic condition to be decomposed the nitrous oxide. Next, the treated liquid flows out in a solid-liquid separation tank 28, and here the floating sludge is settled and returned to the nitrous oxide decomposition tank 14 via a return sludge piping 30. Besides, the supernatant is discharged outside via a treated water piping 31 as the treated water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for removing nitrogen from wastewater, and more particularly, to a method and an apparatus for removing nitrogen from wastewater when treating wastewater containing high concentration of ammonia with a high load.

[0002]

2. Description of the Related Art Ammonia nitrogen contained in wastewater such as sewage, night soil, and industrial wastewater is considered to cause a decrease in dissolved oxygen and a eutrophication phenomenon in closed water bodies such as lakes and inner bays to which water is discharged. Conventionally, as a nitrogen removal technology for removing nitrogen components from these wastewaters, biological nitrification and denitrification treatment using microorganisms has been performed, and a representative example is a modified activated sludge circulation method. In this biological nitrification / denitrification treatment, ammonia nitrogen in wastewater is first oxidized to nitrite or nitric acid in an aerobic state by utilizing the ammonia oxidizing ability of nitrifying bacteria, which are autotrophic bacteria. Thereafter, nitrogen is removed from wastewater by reducing nitrous acid or nitric acid to nitrogen in an anaerobic state by using organic matter or the like in wastewater as an electron donor by the action of a denitrifying bacterium which is a heterotrophic bacterium. Wastewater to which the activated sludge circulation modification is applied is mainly sewage having a relatively low concentration of ammonia nitrogen, and the nitrogen concentration of the discharge water can be reduced to several mg / l.

However, high-concentration ammonia-containing wastewater having an ammonia nitrogen concentration of, for example, 400 mg / l to several thousand mg / l, such as wastewater from a developer wastewater, a chemical factory wastewater, a sludge treatment wastewater, etc., is an activated sludge. It is difficult to reduce by the modified circulation method, and it is difficult to treat wastewater. First, the inventors of the present invention, by a multi-stage tank nitrification treatment using the entrapping immobilization carrier of nitrifying bacteria, ammonia nitrogen concentration is 500mg
/ L high concentration ammonia-containing wastewater was subjected to high-load operation without dilution, and a method capable of reducing the wastewater to about 10 mg / l was developed.

[0004]

In a biological nitrification treatment, a nitrification reaction is performed aerobically, and usually, N
H ₄ —N → (NH ₂ OH) → NO ₂ —N → NO ₃ —N, but nitrous oxide (N ₂ O) is produced as a reaction by-product due to microbial activity and changes in operating conditions. Generated. In particular, in the case of nitrification treatment of high-concentration ammonia-containing wastewater, nitrite-type nitrification reaction in which the production of nitrite nitrogen takes precedence is likely to occur, and in the case of this nitrite-type nitrification treatment, Generated amount increases.

In recent years, this nitrous oxide has been regarded as a greenhouse gas next to carbon dioxide, and also as an ozone depleting gas that destroys the stratospheric ozone layer, and wastewater is one of the sources of nitrous oxide. Treatment facilities have been identified. From such a background, it is necessary to suppress the generation of nitrous oxide in wastewater treatment, and it is particularly important to solve the problem of nitrous oxide in treating high-concentration ammonia-containing wastewater. .

The present invention has been made in view of such circumstances, and suppresses the generation of nitrous oxide generated as a reaction by-product of the nitrification treatment of ammonia-containing wastewater.
It is an object of the present invention to provide a method and an apparatus for removing nitrogen from wastewater that can quickly remove generated nitrous oxide.

[0007]

In order to achieve the above object, the present invention provides a nitrification solution obtained by contacting ammonia-containing wastewater with nitrifying bacteria under aerobic conditions, and converting the nitrifying solution to anaerobic nitrous oxide-decomposing bacteria. Contact under sexual conditions. Further, the present invention, in order to achieve the above object, a high-concentration ammonia-containing wastewater, and a carrier encapsulating and immobilizing nitrifying bacteria that preferentially propagate nitrifying bacteria that are less prone to growth inhibition in the high-concentration ammonia-containing wastewater. And a nitrite decomposing tank for contacting the effluent from the nitrification tank with nitrous oxide decomposing bacteria under anaerobic conditions.

[0008] In order to achieve the above object, the present invention provides:
A nitrification tank in which a high-concentration ammonia-containing wastewater and a carrier entrapping and immobilizing a nitrifying bacterium that preferentially proliferates nitrifying bacteria that are less likely to be inhibited by the high-concentration ammonia-containing wastewater under aerobic conditions, A nitrous oxide decomposing tank in which an effluent from the nitrification tank and nitrous oxide decomposing bacteria are brought into contact under anaerobic conditions, and a denitrifying bacterium and an effluent from the nitrous oxide decomposing tank under anaerobic conditions. And a denitrification tank to be contacted.

According to the present invention, the ammonia-containing wastewater is
A nitrification solution that has been subjected to nitrification treatment by contact with nitrifying bacteria under aerobic conditions is brought into contact with nitrous oxide decomposing bacteria under anaerobic conditions to decompose nitrous oxide. In addition, by installing a nitrification tank in a multi-stage manner, and installing a nitrous oxide decomposition tank between the nitrification tanks, the nitrous oxide generated in the nitrification tank preceding the nitrous oxide decomposition tank is decomposed and removed. In addition, the production of nitrous oxide in the nitrification tank located downstream of the nitrous oxide decomposition tank is suppressed.

[0010] In particular, nitrous oxide is easily generated in the nitrification treatment of wastewater containing ammonia with a high concentration of ammonia nitrogen, so that it is particularly effective as a method and apparatus for removing nitrogen from wastewater containing a high concentration of ammonia.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method and apparatus for removing nitrogen from wastewater according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a configuration diagram illustrating a first embodiment of a wastewater nitrogen removing apparatus according to the present invention, and is suitable when the ammonia concentration in the wastewater is equal to or lower than the medium concentration.

As shown in FIG. 1, the nitrogen removal apparatus 10 for waste water shown in the first embodiment is mainly composed of a nitrification tank 12 and a nitrous oxide decomposition tank 14. Nitrification tank 1
A carrier A (B) containing and immobilizing nitrifying bacteria is accommodated in 2, and an aerator 16 for forming an aerobic condition in the nitrification tank 12 is provided at the bottom of the nitrification tank 12. . Depending on the ammonia nitrogen concentration of the raw water of the wastewater, the carrier is a carrier A encapsulating and immobilizing a nitrifying bacterium that is less likely to be inhibited by a high concentration of ammonia nitrogen, or a carrier B encapsulating and immobilizing a normal nitrifying bacterium. Selected. And raw water inflow pipe 1
The ammonia-containing wastewater that has flowed into the nitrification tank 12 through 8 is brought into contact with nitrifying bacteria in an aerobic state. Next, the nitrification tank 12
The nitrification liquid which has been subjected to the nitrification treatment flows out of the outflow portion 20 into the nitrous oxide decomposition tank 14. The outflow part 20 is provided with a screen 22 for carrier prevention, and the liquid in the nitrification tank 12 is sent to the nitrous oxide decomposition tank 14 through an opening (not shown).

In the nitrous oxide decomposing tank 14, suspended sludge containing nitrous oxide decomposing bacteria is stored, and an underwater stirrer 24 is provided at the bottom to slowly stir the liquid in the tank. Degas the air in the liquid and make the tank anaerobic.
As a result, the nitrification liquid that has flowed into the nitrous oxide decomposition tank 14 comes into contact with nitrous oxide decomposing bacteria under anaerobic conditions, and decomposes nitrous oxide (N ₂ O) generated in the nitrification tank 12. The liquid treated in the nitrous oxide decomposition tank 14 flows out of the water pipe 26 into the solid-liquid separation tank 28, where the suspended sludge is settled and returned to the nitrous oxide decomposition tank via the return sludge pipe 30. On the other hand, the supernatant liquid of the solid-liquid separation tank 28 is discharged out of the apparatus via the treated water pipe 31 as treated water.

As the nitrous oxide-decomposing bacteria accommodated in the nitrous oxide-decomposing tank 14, in addition to the suspended sludge containing the nitrous oxide-decomposing bacteria, a carrier in which the nitrous oxide-decomposing bacteria are immobilized is used in combination. Nitrogen-decomposing bacteria can be maintained in the tank at a high concentration, which is more preferable. As nitrous oxide degrading bacteria,
Facultative anaerobic Pseudomonas, Microco
ccus, Spirillum, Achromobac
ter, Alcaligenes, autotrophic Alca
ricees eutrophus, Paracoc
cus denitrificans, Pseudom
onaspseudoflava, Micrococc
us denitrificans, Tiobacil
rus and Sulfolobus can be used.

According to the first embodiment of the present invention, in a biological nitrification treatment, nitrous oxide (N ₂ O) produced as a reaction by-product due to a change in microbial activity or operating conditions, etc. Can be quickly decomposed and removed in the nitrous oxide decomposition tank 14. This makes it possible to prevent nitrous oxide, which is regarded as a problem as a greenhouse gas or an ozone-depleting gas that destroys the stratospheric ozone layer, from being released into the atmosphere.

FIG. 2 is a block diagram for explaining a second embodiment of the nitrogen removal apparatus for waste water of the present invention. In the case where a multi-stage nitrification tank is provided in order to cope with high-concentration ammonia-containing waste water. It is. The same reference numerals are given to the same devices and members as those in FIG. 1 and the description is omitted. The nitrogen removing device 10 according to the second embodiment of the present invention includes, as shown in FIG.
A nitrous oxide decomposition tank 14 is provided between the first-stage nitrification tank 12A and the second-stage nitrification tank 12B.

The first and second nitrification tanks 12A, 12A
The structure of the B and nitrous oxide decomposition tank 14 is the same as that of the first embodiment. However, nitrifying bacteria that are not easily inhibited by high-concentration ammonia-nitrogen are inhibited in the first-stage nitrification tank 12A. The first carrier B that has been comprehensively fixed is stored. The carrier B of the first-stage nitrification tank is provided in the second-stage nitrification tank 12B in accordance with the concentration of ammonia flowing into the second-stage nitrification tank.
Either the carrier A or the carrier A in which ordinary nitrifying bacteria are entrapped and immobilized.

According to the second embodiment of the present invention, the nitrogen removal rate of the high-concentration ammonia-containing wastewater can be improved by forming the nitrification tanks 12A and 12B in multiple stages, and the first stage can be improved. The nitrous oxide generated in the nitrification tank 12A can be decomposed and removed in the nitrous oxide decomposition tank 14. Further, by providing a nitrous oxide decomposition tank 14 in front of the second nitrification tank 12B, the second nitrification tank 1
The generation of nitrous oxide in 2B can be suppressed.

In particular, in the case of wastewater containing a high concentration of ammonia, such as wastewater from a developing lab wastewater, a chemical factory wastewater, a sludge treatment wastewater, etc., nitrite-type nitrification in which a large amount of nitrite nitrogen is generated. The treatment is easily performed, and there is a close relationship between the concentration of nitrate nitrogen produced at this time and the amount of nitrous oxide produced. Therefore, the second embodiment of the present invention is particularly effective for high-concentration ammonia-containing wastewater.

FIG. 3 is a block diagram illustrating a third embodiment of the wastewater nitrogen removing apparatus according to the present invention. In order to further improve the nitrogen removal rate of high-concentration ammonia-containing wastewater,
This is a case where a denitrification tank is provided after a multi-stage nitrification tank. The same devices and members as those in the first and second embodiments are denoted by the same reference numerals and description thereof is omitted. A nitrogen removing apparatus 10 according to a third embodiment of the present invention is a combination of the second embodiment and a denitrification tank, and includes a first-stage nitrification tank 12A,
The nitrous oxide decomposition tank 14, the second-stage nitrification tank 12B, and the denitrification tank 32 are arranged in this order. In addition, suspended sludge containing denitrifying bacteria is stored in the denitrification tank 32, and an underwater agitator 24 is provided at the bottom of the denitrification tank 32, similarly to the nitrous oxide decomposition tank 14. Thus, the liquid flowing from the second-stage nitrification tank 12B is brought into contact with the denitrifying bacteria under anaerobic conditions. The sludge settled in the solid-liquid separation tank 28 is returned to both the nitrous oxide decomposition tank 14 and the denitrification tank 32 via the return sludge pipe 30.

According to the third embodiment of the present invention, the second
In addition to achieving the same effects as the embodiment,
In the final stage of the denitrification tank 32, the second-stage nitrification tank 12B
Since the nitrate nitrogen and nitrite nitrogen generated in the above are denitrified, the nitrogen removal rate can be improved.

[0022]

【Example】

(Embodiment 1) Embodiment 1 is a case where the apparatus is formed by using an apparatus composed of two tanks of the nitrification tank and the nitrous oxide decomposition tank described with reference to FIG. In the nitrification tank, an entrapping immobilization carrier in which nitrifying bacteria which are hardly hindered by growth inhibition by high-concentration ammonia nitrogen is immobilized is stored at a filling rate of 20%.
0 kg-N / m ^3. days. In the nitrous oxide decomposition tank, suspended sludge containing nitrous oxide decomposing bacteria was used.

As a comparative example, a multi-stage nitrification treatment in which three nitrification tanks having the same conditions as those used in Example 1 were arranged in series was performed. As the raw water of the ammonia-containing wastewater used in the test, inorganic wastewater of a chemical factory having an ammonia nitrogen (NH ₄ —N) concentration of 600 mg / l was used in both Example 1 and Comparative Example. Table 1 shows the results of Example 1 and Comparative Example. The values in Table 1 are
It is a measured value of the effluent of each tank.

[0024]

[Table 1] From the results in Table 1, it was found that both of Example 1 and Comparative Example had about 70% of NH ₄ —N in raw water in the nitrification tank (Comparative Example was the first stage).
% Is converted to NO ₂ -N and N ₂ O is 3.33 in the example.
mg / l, and 3.69 mg / l in the comparative example.

[0025] Then, in the comparative example, N ₂ O in the nitrification tank of the second stage increases to 8.2 mg / l, N ₂ O in the nitrification tank of the third stage is 1.44 mg / l There was no sufficient reduction. On the other hand, in Example 1, N ₂ O was removed to 0.05 mg / l in the nitrous oxide decomposition tank, and at the same time, NO ₂ -N was denitrified to 10 mg / l or less.

Therefore, the use of the apparatus according to the first embodiment of the present invention makes it possible to remove nitrous oxide generated in the nitrification tank to a low concentration. (Embodiment 2) In Embodiment 2, a multi-stage nitrification tank is provided to cope with high-concentration ammonia-containing wastewater. The first-stage nitrification tank and the nitrous oxide decomposition tank described with reference to FIG. And a second-stage nitrification tank.

In the first and second nitrification tanks, an entrapping immobilization carrier in which nitrifying bacteria are entrapped and immobilized is accommodated at a filling rate of 20%, and the load of the nitrification tanks is set at the first and second stages. 1.0 for both eyes
kg-N / m ^3. days. In the nitrous oxide decomposition tank, suspended sludge containing nitrous oxide decomposing bacteria was used. As a comparative example, the same nitrification tank as in Example 1 was subjected to three-stage treatment.

The raw water of the ammonia-containing wastewater subjected to the test was prepared using ammonia nitrogen (NH ₄ −) in both Example 2 and Comparative Example.
N) Chemical factory inorganic wastewater with a concentration of 1000 mg / l was used. Table 2 shows the results of Example 2 and Comparative Example. Table 1
Are the measured values of the effluent from each tank.

[0029]

[Table 2] From the results shown in Table 2, in both Example 2 and Comparative Example, about 70% of the NH ₄ —N in the raw water was NO ₂ —N in the first-stage nitrification tank.
Is converted to that, N ₂ O is Example 2 in 5.47mg / l,
In the comparative example, 5.12 mg / l was produced.

[0030] Then, in the comparative example, N ₂ O in the nitrification tank of the second stage is significantly increased to 48.2 mg / l, N ₂ O is 3.44mg / l in the nitrification tank in the third stage Met. In contrast, in the case of Example 2, N ₂ O was reduced to 0.35 mg / l in the nitrous oxide decomposition tank, and
_2- N was denitrified to 10 mg / l. In the case of Example 2, nitrous oxide hardly increased in the second-stage nitrification tank.

As can be seen from the results, when the high-concentration NO ₂ —N generated in the first-stage nitrification tank is carried over to the second-stage nitrification tank as it is, a remarkable increase in N ₂ O occurs. Admitted. Therefore, by providing a nitrous oxide decomposition tank to decompose and remove nitrous oxide and simultaneously removing NO ₂ -N, it is possible to suppress the generation of N ₂ O in the second and subsequent nitrification tanks.

Therefore, by using the apparatus of the second embodiment of the present invention, the concentration of ammonia nitrogen in the treated water can be reduced and the generation of nitrous oxide can be suppressed. (Embodiment 3) In Embodiment 3, a denitrification tank is provided after the second nitrification tank of Embodiment 2, and the first nitrification tank, the nitrous oxide decomposition tank, and the second nitrification tank described in FIG. 4th stage nitrification tank and denitrification tank
This was performed using an apparatus constituted by a tank.

In the first and second nitrification tanks, an entrapping immobilization carrier entrapping and immobilizing nitrifying bacteria is stored at a filling rate of 20%, and the load of the nitrification tanks is reduced to the first and second stages. 1.0 for both eyes
kg-N / m ^3. days. In the nitrous oxide decomposition tank, suspended sludge containing nitrous oxide decomposing bacteria was used. In the denitrification tank,
Suspended sludge containing denitrifying bacteria was used. As a comparative example, the result of the comparative example in Example 2 was used as it was.

The raw water of the ammonia-containing wastewater subjected to the test was ammonia nitrogen (NH ₄ −) in both Example 2 and Comparative Example.
N) Chemical factory inorganic wastewater with a concentration of 1000 mg / l was used. Table 3 shows the results of Example 3, and the numerical values are the measured values of the effluent of each tank.

[0035]

[Table 3] From the results in Table 3, in the first nitrification tank of Example 3, about 70% of the NH ₄ —N in the raw water was converted to NO ₂ —N,
5.30 mg / l of N ₂ O was produced.

Thereafter, N ₂ O is placed in a nitrous oxide decomposition tank.
Is reduced to 0.37 mg / l, at the same NO ₂ -N simultaneously it has been denitrified to 10 mg / l. Then, while the remaining NH ₄ —N is reduced to 10 mg / l or less in the second-stage nitrification tank, the N ₂ O slightly increases to 1.63 mg / l. / L, and the remaining NO ₂ -N was also denitrified to 10 mg / l or less.

Therefore, the use of the apparatus according to the third embodiment of the present invention makes it possible to significantly increase the nitrogen removal rate and further suppress the generation of nitrous oxide.

[0038]

As described above, according to the method and apparatus for removing nitrogen from wastewater of the present invention, it is possible to suppress the generation of nitrous oxide generated as a reaction by-product of the nitrification treatment of wastewater containing ammonia. The generated nitrous oxide can be quickly removed. Therefore, nitrous oxide, which is regarded as a problem as a greenhouse gas or an ozone layer-depleting gas that destroys the stratospheric ozone layer, can be prevented from being released to the atmosphere.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a first embodiment of a nitrogen removing device of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a second embodiment of the nitrogen removing apparatus of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration of a third embodiment of the nitrogen removing apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Nitrogen removal apparatus 12 ... Nitrification tank 12A ... First-stage nitrification tank 12B ... Second-stage nitrification tank 14 ... Nitrous oxide decomposition tank 16 ... Aeration device 18 ... Raw water supply pipe 22 ... Screen 24 ... Underwater stirrer 28: solid-liquid separation device 30: return sludge piping 32: denitrification tank

 ──────────────────────────────────────────────────の Continued from the front page (72) Inventor Kazuhiko Noto 1-1-1 Uchikanda, Chiyoda-ku, Tokyo Inside Hitachi Plant Construction Co., Ltd.

Claims (5)

[Claims] 1. A method for removing nitrogen from wastewater, comprising: contacting nitrifying solution with nitrifying bacteria by contacting nitrifying bacteria with ammonia-containing wastewater under aerobic conditions, and contacting the nitrifying solution with nitrous oxide-decomposing bacteria under anaerobic conditions. . 2. The ammonia-containing wastewater is a high-concentration ammonia-containing wastewater in which nitrite nitrogen is easily generated by the nitrification treatment, and the nitrifying bacteria is less susceptible to growth inhibition by a high-concentration ammonia-nitrogen. The method for removing nitrogen from wastewater according to claim 1, wherein the method is a carrier for entrapping and immobilizing nitrifying bacteria in which bacteria are preferentially propagated. 3. The method according to claim 1, wherein said high-concentration ammonia-containing wastewater is contacted with a carrier, on which a nitrifying bacterium which preferentially proliferates nitrifying bacteria which is hardly inhibited by the high-concentration ammonia-containing wastewater is immobilized and immobilized. A nitrogen nitrification tank, and a nitrous oxide decomposition tank for bringing an effluent from the nitrification tank into contact with nitrous oxide decomposing bacteria under anaerobic conditions. 4. A nitrification tank having a plurality of nitrification tanks and a nitric oxide decomposition tank having at least one of the nitrification tanks arranged in the plurality of stages.
4. The method according to claim 3, wherein the step is disposed after the nitrification tank in the first stage.
Wastewater nitrogen removal equipment. 5. The method according to claim 1, wherein the high-concentration ammonia-containing wastewater is brought into contact with a carrier on which a nitrifying bacterium which preferentially proliferates nitrifying bacteria which is hardly inhibited by the high-concentration ammonia-containing wastewater is immobilized under aerobic conditions. A nitrification tank, a nitrite decomposing tank for bringing an effluent from the nitrification tank into contact with nitrous oxide decomposing bacteria under anaerobic conditions, and an effluent from the nitrous oxide decomposing tank and denitrifying bacteria. An apparatus for removing nitrogen from wastewater, comprising: a denitrification tank contacted under anaerobic conditions.