JPH09276896A - Denitrification treatment of waste water containing ammonia - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform efficient denitrification treatment, in subjecting waste water containing a specific amt. or more of ammonia to denitrification treatment, by dividing waste water into two parts and subjecting one part to biological nitrification treatment to form nitrite ions to mix the treated part with the other part and decomposing formed ammonium nitrite. SOLUTION: In the denitrification treatment of waste water containing ammonia such as excretion type sewage, at first, raw water (waste water with an NH4 <+> concn. of 500mg-N/L or more) introduced from piping 10 is equally divided into first and second flow parts and the first flow part is introduced into an aerobic tank 1 from piping 11 to perform biological NO2 type nitrification under an aerobic condition by nitrifying bacteria to form NO2 <-> ions. NO2 <-> of the nitrification treatment soln. of the first flow part and NH4 <-> of the second flow part (raw water) are mixed to form NH4 NO2 . This mixed soln. is supplied to a decomposition column 2 to be inorganically decomposed and denitrified and the treated soln. is sent to a gas venting tank 4 from piping 15 through a water cooling pipe 3 to separate N2 gas and discharged out of the system through piping 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for denitrifying wastewater containing ammonia, and more particularly, to a method for biologically nitrifying wastewater containing ammonia to perform ammonium nitrification (NH 3).
₄ NO ₂ ) and decompose the generated NH ₄ NO ₂ into nitrogen (N ₂ ) gas.

[0002]

2. Description of the Related Art For night soil sewage, 3000-4000 p
Since it contains pm of ammonia nitrogen,
For the treatment of night soil sewage, it is necessary to remove it efficiently. Conventionally, a biological nitrification denitrification method has been widely used as a nitrogen removal process.

The nitrification reaction in the conventional biological nitrification denitrification method is a two-step sequential reaction by two kinds of nitrifying bacteria, nitrite and nitric acid bacterium, and NH ₄ ⁺ is oxidized to NO ₂ ⁻ by nitrite. Then, it is oxidized to NO ₃ ⁻ by nitric acid bacteria. Then, the produced NO ₃ ⁻ is biologically denitrified into N ₂ gas.

Such a biological nitrification denitrification method has many advantages, but on the other hand, a large amount of O ₂ is required for nitrification; it is necessary to supply BOD as a hydrogen donor for denitrification. There are drawbacks such as;

On the other hand, in the nitrification reaction, if nitrification can be maintained in the nitrous acid (NO ₂ ) type, O ₂ required for nitrification is required.
On which can be reduced BOD amount when the amount and biological ^{_{denitrification, NH 4 + + NO 2 -}} → N 2 ↑ + 2H _{since 2} O can be introduced chemical denitrification process that, even more necessary amount of O ₂ Can be reduced, which is extremely advantageous industrially.

The 28th Annual Meeting of the Japan Society on Water Environment (1)
996) “Examination of nitriding treatment method utilizing NH ₄ NO ₂ production by living organisms” describes NH produced by biological nitrification.
It has been reported that ₄ NO ₂ can be decomposed at high speed by a catalyst.

In order to carry out such decomposition of NH ₄ NO ₂ , in JP-A-2-198695, the pH in the aerobic tank is adjusted to 6 to 8 and NO in biological nitrification.
_A method has been proposed in which NO ₂ -type nitrification is carried out by keeping ₂ ^- ions at 50 mg-N / L or more. This method has a pH of 6-
If ion concentration 50 mg-N / L or more, ^- 8, NO ₂
It utilizes that nitric acid bacterium is not inhibited and only nitric acid bacterium is selectively inhibited and NO ₂ type nitrification can be performed.

Further, in Japanese Patent Laid-Open No. 2-198696, NH ₄ ⁺ concentration and alkalinity in waste water are measured, and acid or alkali is added to control the nitrification rate so that the equivalent ratio becomes a predetermined value. A method of doing so is disclosed.

Further, in Japanese Unexamined Patent Publication No. 3-161095, NH ₄ NO is obtained by anaerobically treating human sewage and performing biological nitrification.
₂ is generated, and then NH ₄ NO ₂ is decomposed into N _2, and in JP-A-3-161096, organic waste water is aerobically treated to decompose BOD and biological nitrification. NH ₄ NO ₂ is produced by, then, NH ₄
A method of decomposing NO ₂ into N ₂ has been proposed.

Among these methods, for example, Japanese Unexamined Patent Publication No.
In the method described in Japanese Patent No. 161096, in order to generate NH ₄ NO ₂ by biological nitrification, NH ₄ ⁺ concentration and alkalinity in wastewater are measured based on the following principle. By adding an acid or an alkali so that the equivalent ratio of 1 is 1, the nitrification by nitrifying bacteria is carried out to obtain a treated water of NH ₄ / NO ₂ = 1 with a nitrification rate of 50%. Type nitrification and chemical decomposition of NH ₄ NO ₂ are carried out stepwise to efficiently carry out nitrification denitrification.

That is, in the wastewater, there are substances having various pH buffering powers such as bicarbonates, carbonates and phosphates, that is, buffers. Then, nitrification proceeds and NO ₂ ⁻ ions are generated, and the buffer is consumed. When all the buffer is consumed, the pH drops sharply and nitrification stops. Therefore, the NH ₄ ⁺ concentration in the wastewater and the buffer concentration, that is, the alkalinity is measured, and the buffer is adjusted by adding an acid or an alkali to adjust this equivalence ratio, and the nitrification rate is set to a desired value. You can That is, NH ₄ ^{+ in the} wastewater
If the concentration and alkalinity are equivalent, NH in the wastewater
Half of ₄ ⁺ is nitrified and NH ₄ NO ₂ (NH ₄ / NO ₂ =
Since the buffer does not remain when 1) is generated, p
H is lowered, nitrification is stopped, and the nitrification rate becomes 50%. Also,
When the ammonia concentration is higher than the alkalinity, NH ₄ ⁺ remains when the buffer is completely digested and nitrification stops when the nitrification amount is smaller, and the nitrification rate becomes less than 50%. On the other hand, when the ammonia concentration is lower than the alkalinity, the pH does not decrease because the buffer remains even at the stage where the nitrification has progressed to half, and the nitrification further proceeds and the nitrification rate is 50%.
% Will be exceeded.

By the way, the biological nitrification reaction is expressed by the following basic equation.

NH ₄ ⁺ +3/2 O ₂ → NO ₂ ⁻ + H ₂ O + 2H ⁺ Conventionally, in order to prevent a decrease in pH due to generated H ⁺ , pH control is usually performed to perform 100% nitrification.

On the other hand, the form of N in the waste water is mostly NH ₄ ⁺ -N, and the source of the generation is due to the decomposition of the amino group of the protein.
When BOD coexisting in the waste water is decomposed, there is the generation of CO _2, which the NH ₄ ⁺ are bonded, NH ₄ ⁺ forms NH ₄
It becomes HCO ₃ . The reaction formula of the nitrification reaction of NH ₄ HCO ₃ without adjusting the pH is as follows.

NH ₄ HCO ₃ +3/4 O ₂ → 1/2 NH ₄ N
When O ₂ +3/2 H ₂ O + CO ₂ NH ₄ NO ₂ is produced, all NH ₄ HCO ₃ in the waste water is consumed, and if no other buffer is present in the liquid, the pH will drop and nitrification will stop. That is, NH ₄ / NO ₂
The reaction stops spontaneously when = 1.

Therefore, if the buffer amount is equimolar to NH ₄ ⁺ , it is possible to obtain treated water of NH ₄ / NO ₂ = 1 without adjusting the pH, but due to factors such as the pretreatment step, NH ₄ ⁺ When NH ₄ / NO ₂ = 1 is not obtained due to the equivalence relationship between the alkalinity and the alkalinity, it is necessary to measure the NH ₄ ⁺ concentration and the buffer amount of the solution, that is, the alkalinity, and adjust the equivalent ratio in advance. Becomes That is, in the case of NH ₄ / NO ₂ > 1, a predetermined amount of alkali is added, and in the case of NH ₄ / NO ₂ <1, the acid is added.

[0017]

As described above, in biological nitrification, the NH ₄ ⁺ concentration and alkalinity in the wastewater are used as the control criteria for performing NO ₂ -type nitrification to generate NH ₄ NO _2. The method described above requires an apparatus and operation for measuring the NH ₄ ⁺ concentration and alkalinity and adding an acid or an alkali based on the measured values, and is not easy to carry out.

If the method described in JP-A-2-198695 utilizes the selective inhibitory effect of nitrifying bacteria due to the presence of NO ₂ ⁻ ions, it is not necessary to measure the alkalinity, etc. to obtain a selective inhibitory effect of nitrifying bacteria stably and reliably, NO ₂ ^- ion concentration 500 mg-N /
It has been found that L or more is required. That is, when applying this method to the production of NH ₄ NO ₂ ,
After O ₂ type nitrification, it is necessary that the NO ₂ ⁻ ion concentration in the nitrification treatment liquid in which NH ₄ NO ₂ is generated is 500 mg-N / L or more. To do this, the NH ₄ ⁺ concentration in the raw water is 1
It is necessary to be 000 mg-N / L or more. Therefore, this method cannot be applied to wastewater having an NH ₄ ⁺ concentration lower than 1000 mg-N / L.

The present invention solves the above conventional problems and can be applied to the biological nitrification denitrification of ammonia-containing wastewater having a NH ₄ ⁺ concentration lower than 1000 mg-N / L. , without the need for measurement of alkalinity, NH ₄ performed easily and reliably NO ₂ type nitrification
It is an object of the present invention to provide a method for producing NO ₂ and performing an efficient denitrification treatment.

[0020]

The method for denitrifying wastewater containing ammonia according to the present invention comprises 500 mg-ammonia of ammonia.
In a method for denitrifying a wastewater containing N / L or more, the wastewater is divided into two parts, one of them is subjected to a biological nitrification treatment to generate nitrite ions, and then the other is mixed to decompose ammonium nitrite formed. It is characterized by doing.

In the denitrification treatment method for wastewater containing ammonia according to the present invention, wastewater having an NH ₄ ⁺ concentration of 500 mg-N / L or more is divided into two parts (hereinafter, sometimes referred to as "first stream"). Is biologically nitrified to produce NO ₂ ⁻ ions.
That, NO ₂ ^- and a stream portion of higher ion concentration 500mg-N / L. This stream fraction is, NO ₂ ^- ion concentration 500 mg-N
/ L or more, nitrification becomes NO ₂ type due to the selective inhibitory effect of nitrifying bacteria due to the presence of NO ₂ ⁻ ions, and NO ₃ ⁻ is hardly generated. Then, the NO ₂ ^- ion concentration 500m
The nitrification treatment liquid for the first flow of g-N / L or more is mixed with the other flow when the waste water is divided into two (hereinafter sometimes referred to as "second flow"). This second stream is NH ₄ ⁺ concentration 5
200 mg-N / L or more in the first flow amount of NO ₂ ^- from those containing NH ₄ ⁺ ions and finally the amount, mixing the second stream component and a first flow portion of nitrified liquid Then NH ₄ NO
₂ will definitely generate.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a denitrification treatment method for wastewater containing ammonia according to the present invention.

As shown in the figure, in the present invention, first, the raw water (NH ₄ ⁺ concentration 500 mg-N
/ L or more of wastewater) is divided into an equal amount into a first stream and a second stream, and the first stream is introduced from a pipe 11 into an aerobic tank 1 equipped with an aeration pipe 1A under aerobic conditions. Biological NO by nitrite
Type ₂ nitrification is performed to generate NO ₂ ⁻ ions. Then, the first stream of the nitrification treatment liquid extracted from the pipe 12 and the pipe 1
Mix the second stream from 3 (raw water).

This mixed solution contains NH 2 of the second stream (raw water).
NH ₄ NO ₂ is produced by mixing ₄ ⁺ and the NO ₂ ⁻ of the nitrification treatment liquid of the first stream in an equivalent amount. This mixed liquid is used for the heater 2
A is supplied to the decomposition tower 2 filled with the catalyst 2B,
NH ₄ NO ₂ is inorganically decomposed and denitrified into N ₂ gas. The treated water in the decomposition tower 2 is extracted from the pipe 15, sent through the water cooling pipe 3 to the degassing tank 4, N ₂ gas is separated, and the treated water is discharged out of the system through the pipe 16.

Thus, the raw water is divided into two, and only the first stream is subjected to biological nitrification with nitrifying bacteria to produce NO ₂ ⁻ , which is mixed with the second stream containing NH ₄ ^+. NH ₄ NO
₂ to generate, by the generated NH ₄ NO ₂ to denitrification in inorganically N ₂ gas, is it possible to perform efficient denitrification.

In the present invention, it is optimal that the first and second streams are equal in quantity, but it is not necessary that they are exactly equal in quantity. Min = 50-5
A sufficient effect can be obtained in the range of 5:45 to 50.

[0028]

The present invention will be described more specifically with reference to the following examples and comparative examples.

Example 1 The treatment of ammonia-containing water having the water quality shown in Table 1 was performed by the method shown in FIG. 1 at a flow rate of 1 L / day for the first stream and 1 L / day for the second stream.

In the aerobic tank, the filling rate of immobilized nitrifying bacteria is 2
The treatment was carried out at 0% and a residence time of 1 day.

The decomposition tower 2 was filled with 0.5% Pt-alumina as a catalyst, and the temperature was 200 ° C. and the pressure was 25 kg / cm.
^2. Treated with a residence time of 20 minutes.

Table 1 shows the quality of treated water in each step.

From Table 1, according to the method of the present invention, by simply dividing the raw water into two, NH ₄ NO ₂ is produced and decomposed without the need for sophisticated control and complicated operation, and high water quality is obtained. It is clear that the treated water can be obtained.

[0034]

[Table 1]

Comparative Example 1 As shown in Table 2, raw water having an NH ₄ ⁺ concentration lower than 500 mg-N / L was treated in the same manner as in Example 1, and the obtained treated water is shown in Table 2.

[0036]

[Table 2]

From Table 2, NH ₄ ⁺ concentration 500 mg-N / L
It is clear that NO ₂ -type nitrification cannot be performed with raw water of less than 1.

[0038]

As described above in detail, according to the denitrification treatment method for wastewater containing ammonia of the present invention, the denitrification of wastewater containing ammonia for decomposing NH ₄ NO ₂ produced by NO ₂ type nitrification is produced. It is possible to surely generate NH ₄ NO ₂ and perform an efficient denitrification process without complicated control in the process.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example method of a method for denitrifying wastewater containing ammonia according to the present invention.

[Explanation of symbols]

 1 aerobic tank 2 decomposition tower 3 water cooling tube 4 degassing tank

Claims (1)

[Claims] 1. A method for denitrifying a wastewater containing 500 mg-N / L or more of ammonia, wherein the wastewater is divided into two, one of which is subjected to a biological nitrification treatment to generate nitrite ions, and the other is then treated. A method for denitrifying wastewater containing ammonia, which comprises decomposing ammonium nitrite produced by mixing.