JP2010000480A - Effective denitrification method for organic raw water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a denitrification method for organic raw water can prevent the production of gaseous nitrogen and dinitrogen monoxide in a nitrification tank in a denitrification method adopting a nitrous acid type nitrification process. <P>SOLUTION: The method for denitrification of the organic raw water includes the nitrous acid type nitrification process in which the organic raw water containing ammonia nitrogen is oxidized to nitrite nitrogen and a denitrification process in which gaseous nitrogen is produced from effluent from the nitrification tank. As a pretreatment process of the denitrification method of the organic raw water, a BOD decomposition process, in which organic waste water containing ammonia nitrogen is introduced into a BOD decomposition tank 1, where an organism carrier 8 is charged and aeration amount is controlled so that dissolved oxygen amount is ≤2.8 mg/L, to decompose organic materials, is provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an efficient method for denitrifying organic raw water.

  Conventionally, as a method for denitrifying a nitrogen-containing liquid, there is a nitrification process in which ammonia nitrogen is oxidized to nitrite nitrogen by the action of ammonia oxidizing bacteria, and nitrite nitrogen is oxidized to nitrate nitrogen by nitrite oxidizing bacteria. , A two-stage biological reaction with a denitrification process in which these nitrite nitrogen and nitrate nitrogen are converted to nitrogen gas by using organic matter such as methanol as an electron donor by denitrifying bacteria which are heterotrophic bacteria. Biological nitrification and denitrification methods are common.

  However, the nitrification / denitrification treatment using such heterotrophic bacteria has a drawback that a large amount of aeration power is required because ammonia nitrogen is nitrified until it becomes nitrate nitrogen via nitrous acid.

  As means for overcoming the drawbacks, a nitrite-type nitrification step for leaving a part of ammonia nitrogen, and reacting both ammoniacal nitrogen as an electron donor and nitrite nitrogen as an electron acceptor under anaerobic conditions, A denitrification method including a denitrification step for generating nitrogen gas is disclosed (Patent Document 1).

Here, when the denitrification method disclosed in Patent Document 1 is performed using organic raw water, dinitrogen monoxide (N ₂ O ↑) is generated in the nitrite type nitrification step in the nitrite type nitrification step, Nitrogen gas (N ₂ ↑) was observed as a by-product.

Nitrous oxide (N ₂ O) is a 320 times stronger greenhouse gas than carbon dioxide, and it can be said that the suppression of its generation is urgent from the viewpoint of preventing global warming and ozone layer destruction.
JP 2006-88092 A

  An object of the present invention is to provide a method for denitrification of organic raw water which prevents generation of nitrogen gas and dinitrogen monoxide in a nitrification tank in a denitrification method employing a nitrite type nitrification step.

The present inventors have result of extensive research in order to solve this problem, nitrite nitrogen ions organic in raw high BOD (NO ₂ ^-) in the case of the coexistence, the nitrite nitrogen (NO ₂ ^- ) Was subjected to a denitrification reaction, and dinitrogen monoxide (N ₂ O ↑) was produced as a by-product. The present invention made on the basis of the above knowledge, an organic raw water containing ammonia nitrogen is introduced into a nitrification tank, and oxidized to nitrite nitrogen by the action of ammonia oxidizing bacteria, In the denitrification method of organic raw water comprising the denitrification step of introducing the effluent water from the nitrification tank into the denitrification tank and generating nitrogen gas by the action of denitrifying bacteria, before the nitrite type nitrification step, Organic wastewater containing ammonia nitrogen is introduced into the BOD decomposition tank where the aeration amount is controlled so that the biological carrier is introduced and the dissolved oxygen amount (hereinafter referred to as “DO”) is 2.8 mg / L or less. Thus, a BOD decomposition process for decomposing organic substances is provided.

  The invention according to claim 2 is the nitrite type in which the nitrite type nitrification step oxidizes a part of ammonia nitrogen to nitrite nitrogen by the action of ammonia oxidizing bacteria in the denitrification method of organic waste water according to claim 1 Anaerobic that is a nitrification process and the denitrification process generates nitrogen gas by the action of autotrophic microorganisms using nitrite nitrogen generated in the nitrite type nitrification process as an electron acceptor and remaining ammonia nitrogen as an electron donor. It is a characteristic ammonia oxidation reaction step.

  The invention described in claim 3 is characterized in that in the method for denitrifying organic waste water described in claim 2, the autotrophic microorganism is anammox.

  According to a fourth aspect of the present invention, in the denitrification method for organic waste water according to the first aspect, the denitrification step uses nitrite nitrogen as an electron acceptor and organic matter as an electron donor. It is a normal denitrification step for generating gas.

  In the method for denitrifying organic raw water according to claim 1, in the method for denitrifying organic raw water comprising a nitrite type nitrification step and a denitrification step, a biological carrier is introduced and the amount of dissolved oxygen is 2.8 mg / By introducing a BOD decomposition process that decomposes organic matter by introducing it into a BOD decomposition tank that controls the amount of aeration so that it is less than or equal to L, the BOD of treated water introduced into the nitrite type nitrification process is reduced . As a result, in the process where nitrous acid is generated in the nitrite-type nitrification step, it is possible to solve the problem that denitrification occurs due to coexistence of BOD and dinitrogen monoxide is generated as a byproduct.

  In addition, although the technique of performing BOD decomposition | disassembly using activated sludge without using a biological carrier is known, in this case, the sedimentation pond for separating activated sludge behind the BOD decomposition tank, and the separated activity The sludge must be returned to the BOD decomposition tank to return the sludge, which complicates the facilities and makes the operation difficult. On the other hand, according to the present invention in which BOD decomposition is performed using a biological carrier, generation of dinitrogen monoxide can be suppressed without causing these problems.

  In addition, by controlling the amount of aeration so that DO is 2.8 mg / L or less in the BOD decomposition step, it is possible to suppress the metabolism of ammonia oxidizing bacteria in the BOD decomposition tank (to suppress the progress of the nitrification reaction). It becomes possible. For this reason, the coexistence state of a high BOD organic substance and nitrous acid occurs in a BOD decomposition tank, a denitrification reaction arises, and the problem that nitrous oxide is produced as a by-product can be solved.

According to a second aspect of the present invention, the nitrite type nitrification step is a nitrite type nitrification step in which a part of ammonia nitrogen is oxidized to nitrite nitrogen by the action of ammonia oxidizing bacteria, and the denitrification step is the nitrous type nitrification step. In the case of an anaerobic ammonia oxidation reaction process in which nitrogen gas is generated by the action of autotrophic microorganisms using nitrite nitrogen generated in the nitrate type nitrification process as an electron acceptor and remaining ammonia nitrogen as an electron donor, It is considered that ammonia nitrogen and nitrite nitrogen are decomposed into nitrogen gas (N ₂ ) by the following reaction.

That is, in order to efficiently perform denitrification in the anaerobic ammonia oxidation reaction step, the content ratio of ammonia nitrogen and nitrite nitrogen in the water to be treated introduced into the anaerobic ammonia oxidation reaction step is NO ²⁻ / NH. ^{4 +} = 0.57 / 0.43 = 1.32 According to the present invention, the nitrogen source is nitrogen gas or dinitrogen monoxide before the introduction of the anaerobic ammonia oxidation reaction step as described above. The problem of being lost as a gas is solved, and the control of the nitrification rate becomes easy.

  FIG. 1 is a block diagram showing an example of an apparatus suitable for carrying out the present invention. An apparatus for carrying out the present invention shown in FIG. 1 includes a BOD decomposition tank 1, a nitrification tank 2, an anaerobic ammonia oxidation reaction tank 3, a BOD decomposition tank DO meter 4, a BOD decomposition tank aeration apparatus 5, A nitrification tank DO meter 6 and a nitrification tank aeration apparatus 7 are configured.

  The organic raw water introduced into the BOD decomposition tank 1 is, for example, sludge return water generated at a sewage treatment plant, and has a relatively high concentration of phosphate ions (30 to 150 mg / L as P) and ammonium ions ( Organic raw water containing N (500 to 1500 mg / L) and further containing magnesium ions (5 to 15 mg / L).

  The present invention relates to a method for denitrification of organic wastewater comprising a nitrite type nitrification step and a denitrification step, wherein a biological carrier is introduced into the preceding stage of the nitrification tank 2 and DO is 2.8 mg / L or less. BOD decomposition tank 1 with controlled aeration amount as described above, and organic wastewater characterized by introducing an organic wastewater containing ammoniacal nitrogen into the BOD decomposition tank 1 and decomposing organic matter In this embodiment, in particular, a partial nitrification step in which a part of ammonia nitrogen is oxidized to nitrite nitrogen by the action of ammonia-oxidizing bacteria, and nitrite nitrogen is used as an electron acceptor. In the denitrification method for organic wastewater, which comprises an anaerobic ammonia oxidation reaction step of generating nitrogen gas by the action of autotrophic microorganisms using the treated ammonia nitrogen as an electron donor, a pretreatment step is provided in the previous stage of the nitrite tank 4 The embodiment And explain.

  An anaerobic ammonia oxidation reaction process that generates nitrogen gas by the action of autotrophic microorganisms using nitrite nitrogen as an electron acceptor and remaining ammonia nitrogen as an electron donor is an autotrophic denitrifying microorganism called anammox bacteria. This is an anaerobic ammonia oxidation reaction process to be used.

  In the anaerobic ammonia oxidation tank 3 that performs the anaerobic ammonia oxidation reaction step, sludge of anammox bacteria (not shown) is held.

In the anaerobic ammonia oxidation reaction process using anaerobic ammonia oxidation reaction by anammox bacteria, it is considered that ammonia nitrogen and nitrite nitrogen are decomposed into nitrogen gas (N ₂ ) by the above (chemical formula 1) reaction. .

That is, in order to efficiently perform denitrification in the anaerobic ammonia oxidation reaction step, the content ratio of ammonia nitrogen and nitrite nitrogen in the nitrification tank effluent 12 introduced into the anaerobic ammonia oxidation reaction step is NO _2. ⁻ / NH ₄ ⁺ = 0.57 / 0.43 = 1.32 is desirable, and nitrification is performed so that the nitrification tank effluent 12 that has undergone the partial nitrification step, which is the previous step, has the content ratio. The amount of aeration in the tank 2 is controlled.

  A carrier 9 carrying ammonia-oxidizing bacteria is dispersed in the nitrification tank 2 for performing the partial nitrification process, and the amount of aeration is controlled by controlling the amount of air supplied from the aeration apparatus 7 provided at the bottom. To do.

When aeration is performed in the nitrification tank 2, the nitrification reaction by ammonia-oxidizing bacteria is promoted. However, as described above, nitrite nitrogen ions (NO ₂ ⁻ ) are present in the high BOD organic raw water. In this case, there is a problem that nitrite nitrogen (NO ₂ ⁻ ) undergoes a denitrification reaction and dinitrogen monoxide (N ₂ O ↑) is generated as a by-product.

  In the present invention, the pretreatment for reducing the BOD of the nitrification tank inflow water 11 is performed to solve the above-mentioned problem that occurs in the nitrification step. In addition, since the raw water introduced into the pretreatment process has a high BOD, it is also controlled to prevent nitrite nitrogen ions from being generated in the pretreatment process. The problem of occurrence does not occur.

  In the pretreatment process of the present invention, the organic raw water 10 is introduced into the BOD decomposition tank 1 in which the biological carrier 8 is introduced and the aeration amount is controlled so that the dissolved oxygen amount is 2.8 mg / L or less. This is a BOD decomposition process that decomposes organic matter.

  A carrier 8 carrying BOD degrading bacteria is dispersed in the BOD decomposition tank 1 for performing the BOD decomposition process, and the amount of aeration is controlled by supplying air from the aeration apparatus 5 for the BOD decomposition tank provided at the bottom. This is done by controlling the amount. Moreover, in order to control the amount of aeration so that DO is 2.8 mg / L or less, BOD decomposition tank DO meter 4 is provided.

  By controlling DO to 2.8 mg / L or less, it is possible to selectively perform metabolism of BOD-degrading bacteria while suppressing metabolism of ammonia-oxidizing bacteria. As a result, only the BOD decomposition reaction accompanying the metabolism of the BOD-degrading bacteria selectively proceeds in the tank of the BOD decomposition tank 1, and nitrogen gas and nitrous oxide gas are generated in the tank of the BOD decomposition tank 1. Without this, it becomes possible to reduce the BOD.

  The low BOD nitrification tank inflow water 11 thus obtained was introduced into the nitrification tank 2 and the following ammonia-oxidizing bacteria carried on the carrier dispersed in the nitrification tank 2 were used. The oxygen supply amount from the nitrification tank aeration apparatus 7 is adjusted so that the aerobic state suitable for the partial nitrification reaction can be maintained.

  Here, according to the present invention, the inflow water 11 in the nitrification tank introduced into the nitrification tank 1 has a low BOD due to the pretreatment process. The problem of generating nitrogen gas or the like can be solved.

The content ratio of nitrite nitrogen: ammonia nitrogen = 0.57 mol: 0.43 mol is a content ratio suitable for the denitrification reaction (chemical formula 1) by anaerobic ammonia oxidizing bacteria in the latter anammox process. According to the present invention, as a result of solving the problem that the nitrogen source is lost as nitrogen gas or dinitrogen monoxide gas in the nitrification tank 11, the nitrification tank effluent 12 introduced into the anaerobic ammonia oxidation reaction step. The effect of facilitating the control of the content ratio of ammonia nitrogen and nitrite nitrogen of NO ₂ ⁻ / NH ₄ ⁺ = 0.57 / 0.43 = 1.32 is also obtained.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
(Example)
The apparatus suitable for carrying out the present invention shown in FIG. 1 is used to carry out a denitrification method comprising a BOD decomposition process, a nitrification process and a denitrification process, and the water quality status in the BOD decomposition tank and the nitrification tank The results of measuring the amount of denitrification and the amount of nitrous oxide generated are shown below. In this example, the residence time of the BOD decomposition tank is 6 hours, a cylindrical polyurethane carrier is used as the carrier of the BOD decomposition tank, the carrier charging rate is 10%, and the DO control value is 1.5 mg / L. The residence time in the nitrification tank was 6 hours, and the DO control value was 3.5 mg / L. The other conditions were the same as those conventionally used when the denitrification process was an anammox process.

(Comparative Example 1)
The apparatus suitable for carrying out the present invention shown in FIG. 1 is used to carry out a denitrification method comprising a BOD decomposition process, a nitrification process and a denitrification process, and the water quality status in the BOD decomposition tank and the nitrification tank The results of measuring the amount of denitrification and the amount of nitrous oxide generated are shown below. In this example, the residence time of the BOD decomposition tank is 6 hours, a cylindrical polyurethane carrier is used as the carrier of the BOD decomposition tank, the carrier charging rate is 10%, and the DO control value is 3.5 mg / L. The residence time in the nitrification tank was 6 hours, and the DO control value was 3.5 mg / L. The other conditions were the same as those conventionally used when the denitrification process was an anammox process.

(Comparative Example 2)
Using the apparatus shown in FIG. 2 for the raw water similar to the above example, a denitrification method comprising a nitrification step and a denitrification step is performed by a method that does not have a BOD decomposition step before the nitrification step. The results of measuring the water quality in the nitrification tank, the amount of denitrification, and the amount of nitrous oxide generated are shown below. In this comparative example, the residence time in the nitrification tank was 12 hours, and the DO control value was 3.5 mg / L. The other conditions were the same as those conventionally used when the denitrification process was an anammox process.

Table 4 below summarizes the denitrification amounts and dinitrogen monoxide generation amounts of Examples and Comparative Examples 1 and 2 shown in Tables 1 to 3. In Table 4, “Denitrification amount of (BOD decomposition tank + nitrification tank)” means the amount of denitrification while organic raw water flows into the BOD decomposition tank and flows out of the nitrification tank in both tanks It shows the value divided by the total value of the processing volume. In Table 4, “(N ₂ O generation amount / NH ₄ ⁺ −N load amount) of (BOD decomposition tank + nitrification tank)” is the total value of N ₂ O generation amount generated in both tanks. The value divided by the amount of NH ₄ ⁺ -N in the raw water is shown.

  As shown in Table 4, according to the embodiment according to the present invention, the amount of denitrification in the nitrification process is also generated in the nitrification process compared to Comparative Example 2 in which no BOD decomposition tank is provided. The amount was also significantly suppressed. In addition, in the comparative example 1 which made DO control value 3.5 mg / L, the said effect of this invention was not acquired.

It is a block diagram which shows an example of an apparatus suitable for implementing this invention. It is a block diagram which shows an example of the apparatus used for implementation of the comparative example.

Explanation of symbols

1 BOD decomposition tank 2 nitrification tank 3 anaerobic ammonia oxidation reaction tank 4 DO meter for BOD decomposition tank 5 aeration device for BOD decomposition tank 6 DO meter for nitrification tank 7 aeration apparatus for nitrification tank 8 biological carrier 9 biological carrier 10 Organic raw water 11 Infiltration water in nitrification tank 12 Outflow water in nitrification tank

Claims (4)

A nitrite type nitrification process in which organic raw water containing ammonia nitrogen is introduced into a nitrification tank and oxidized to nitrite nitrogen by the action of ammonia oxidizing bacteria,
In the denitrification method of the organic raw water comprising the denitrification step of introducing the effluent water from the nitrification tank into the denitrification tank and generating nitrogen gas by the action of denitrifying bacteria,
Before the nitrite-type nitrification process, organic wastewater containing ammonia nitrogen is put into a BOD decomposition tank in which the biological carrier is introduced and the aeration amount is controlled so that the dissolved oxygen amount is 2.8 mg / L or less. A method for denitrifying organic raw water, comprising a BOD decomposition step for introducing and decomposing organic matter. The nitrite type nitrification step is a nitrite type nitrification step in which a part of ammonia nitrogen is oxidized to nitrite nitrogen by the action of ammonia oxidizing bacteria,
Anaerobic ammonia oxidation reaction in which the denitrification step generates nitrogen gas by the action of autotrophic microorganisms using nitrite nitrogen generated in the nitrite type nitrification step as an electron acceptor and remaining ammonia nitrogen as an electron donor The method for denitrifying organic raw water according to claim 1, wherein the method is a process.   The method for denitrifying organic raw water according to claim 2, wherein the autotrophic microorganism is anammox. 2. The denitrification step is a normal denitrification step in which nitrogen gas is generated by the action of a denitrifying bacterium using nitrite nitrogen as an electron acceptor and organic matter as an electron donor. Denitrification method for organic wastewater.

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