JPH08206670A - Treatment of ammonia nitrogen-containing waste water - Google Patents

Abstract

PURPOSE: To economically perform the treatment of waste water by suppressing the formation of Br2 and NO3 <-> as by-products and to reduce the consumption amt. of ozone in the treatment of ammonia nitrogen-containing waste water by the addition of ozone in the presence of bromide ions. CONSTITUTION: Ozone is added to ammonia nitrogen-containing waste water in an amt. smaller than an amt. necessary for perfectly decomposing ammonia nitrogen to nitrogen gas. The control of the addition amt. of ozone is performed by installing a reducing nitrogen measuring means 22 measuring the concn. of reducing nitrogen in treated water and a control means 24 controlling the addition amt. of ozone to ammonia nitrogen-containing waste water on the basis of the concn. of reducing nitrogen and regulating the addition amt. of ozone so that the concn. of reducing nitrogen in treated water becomes 0.1-20mgN/L.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method for removing ammoniacal nitrogen by adding ozone in the presence of bromine ions to wastewater containing ammoniacal nitrogen such as various industrial wastewater.

[0002]

2. Description of the Related Art Conventionally, the addition of ozone has been used to oxidize and decompose organic substances in wastewater, but since ammonia nitrogen is highly stable, the ammonia nitrogen in wastewater is oxidized and decomposed by adding ozone. Was thought to be difficult to do. However, recently, it was found that ammonia nitrogen can be oxidized and removed by adding ozone to ammonia nitrogen-containing wastewater in the presence of bromide ion, and a wastewater treatment method using this has been proposed. (JP-A-3-181390, JP-A-4-66190).

In the oxidation and removal of ammonia nitrogen by the addition of ozone in the presence of bromine ion, first, the bromine ion present in the waste water reacts with the added ozone to react with hypobromite ion BrO ⁻ (or Bromate HBr
O) is generated (Equation 1 below). Next, the generated BrO ⁻
(Alternatively, HBrO) reacts with ammoniacal nitrogen to gasify the ammoniacal nitrogen (formula 2 below). As a result, ammoniacal nitrogen is oxidized according to the reaction formula (3) below. O ₃ + Br ⁻ → BrO ⁻ + O ₂ (1) 2NH ₄ ⁺ + 3BrO ⁻ → N ₂ + 3Br ⁻ + 3H ₂ O + 2H ⁺ (2) 2NH ₄ ⁺ + 3O ₃ → N ₂ + 3O ₂ + 3H ₂ O + 2H ⁺ (3)

Therefore, in the treatment of ammoniacal nitrogen-containing wastewater by adding ozone in the presence of bromide ions, Br
^- reacts with the ozone BrO ^- becomes, then NH ₄ ⁺ reacts with Br ^- returns to further BrO react with ozone ^- in which repeated cycles of becoming, Br ^- is a catalytic action Show.

A continuous waste water treatment apparatus for removing ammoniacal nitrogen by adding ozone has, for example, the structure shown in FIG. In FIG. 2, 2 is a reaction tank, 4 is a raw water injection device installed in the upper part of the reaction tank 2, 6 is a raw water injection device 4
A raw water introduction pipe connected to, a reference numeral 8 denotes a bromide ion-containing water introduction pipe connected to the raw water introduction pipe 6 (bromine ion addition mechanism), 1
0 is an air diffuser installed in the lower part of the reaction tank 2, 12 is an ozone-containing gas introduction pipe connected to the air diffuser 10, 14 is an ozone-containing gas generator connected to the ozone-containing gas introduction pipe 12, Reference numeral 16 denotes an exhaust gas discharge pipe connected to the upper portion of the reaction tank 2, 18 denotes an ozone decomposer interposed in the exhaust gas discharge pipe 16, and 20 denotes a treated water discharge pipe connected to the bottom portion of the reaction tank 2. In this device, the raw water introducing pipe 6 and the raw water injecting device 4 constitute a raw water introducing mechanism, and the ozone-containing gas generating device 14, the ozone-containing gas introducing pipe 12 and the air diffuser 10 constitute an ozone adding mechanism.

When wastewater treatment is performed by the apparatus shown in FIG. 2, bromine ion-containing water is added from the bromine ion-containing water introduction pipe 8 to ammoniacal nitrogen-containing wastewater (raw water) flowing through the raw water introduction pipe 6, and this raw water is injected into the raw water. It is introduced from the device 4 into the reaction tank 2. Then, the ozone-containing gas generated by the ozone-containing gas generator 14 is added to the raw water in the reaction tank 2 from the diffuser 10 through the ozone-containing gas introduction pipe 12. As a result, the ammoniacal nitrogen in the raw water is decomposed into nitrogen gas and removed. The treated water from which the ammonia nitrogen has been removed is discharged from the treated water discharge pipe 20. Further, the exhaust gas generated in the reaction tank 2 passes through the ozone decomposer 18 and the exhaust gas exhaust pipe 1
It is discharged from 6.

[0007]

In the treatment of ammoniacal nitrogen-containing wastewater by addition of ozone in the presence of bromide ions, it has been necessary to reduce the concentration of ammoniacal nitrogen in the treated water to the wastewater regulation value or a certain target value. For the purpose, the ozone addition amount is determined by feedforward control or feedback control so that the ammonia nitrogen concentration approaches zero as much as possible.

However, when the inventors of the present invention are studying the practical application of the wastewater treatment, when the amount of ozone added is controlled so that the concentration of ammonia nitrogen in the treated water becomes zero, the bromine gas ( It was noticed that Br ₂ ) was generated and the amount of nitrate nitrogen (NO ₃ ⁻ ) by-produced in the treated water was increased. Since Br ₂ is toxic, it cannot be discharged into the environment as it is. In this case, B
Most of r ₂ is discharged together with the exhaust gas. Therefore,
When Br ₂ is produced as a by-product, a facility for removing Br _{2 in} the exhaust gas must be separately provided, which increases the cost. Further, the NO ₃ ⁻ by-product leads to a decrease in the nitrogen removal rate in the entire process and also increases the ozone consumption amount. . Therefore, the present inventors
A means for suppressing the by-production of ₂ and NO ₃ ⁻ was examined.

The present invention has been made as a result of such a study, and suppresses by-production of Br ₂ and NO ₃ ⁻ as much as possible in the treatment of ammoniacal nitrogen-containing wastewater by adding ozone in the presence of bromine ions. It is an object of the present invention to provide a method for treating wastewater containing ammoniacal nitrogen.

[0010]

Means and Action for Solving the Problems The present inventors have
As a result of various studies to achieve the above-mentioned object, the following findings (a) to (e) were obtained. (A) As can be seen from the reaction formulas 1 and 2, in order to make the concentration of ammonia nitrogen in the treated water zero, the ozone addition amount is controlled so that a constant amount of BrO ⁻ always remains in the water in the reaction tank. Therefore, in the past, ozone was added in excess of the amount required to completely decompose all the ammoniacal nitrogen into nitrogen gas. On the other hand, BrO ^-
In the remaining water, BrO ⁻ , HBrO, and Br ₂ coexist by the equilibrium shown in the following formulas 4 and 5. B of this
Part of r ₂ moves to the gas phase side and is discharged from the reaction tank together with the exhaust gas.

[0011]

Embedded image

As described above, Br ₂ is produced because BrO ⁻ remains in the water in the reaction tank, and BrO ^−.
Remains because the excess ozone is added. Therefore, without adding excess ozone to the water in the reaction tank, by adding an amount of ozone less than that required to completely decompose the ammoniacal nitrogen into nitrogen gas,
It is possible to prevent BrO ⁻ from remaining and prevent Br ₂ from being produced as a by-product. Further, when ozone is added in an amount smaller than that required to completely decompose ammoniacal nitrogen into nitrogen gas, ozone consumption can be reduced, which is economically advantageous.

(B) The reaction of oxidizing and removing ammoniacal nitrogen by adding ozone in the presence of bromide ion is as shown in the above formulas 1 and 2, but the actual reaction process is more complicated. Is. That, NH ₄ ⁺ in the part free of ammonia in the treated water (NH _3), and this NH ₃ is O _3, Br ^- and has Deki reacted BrO ^-
It reacts with (HBrO) to form an amine monobromide (NH ₂ Br), and this NH ₂ Br acts as BrO ⁻ (HBrO) to produce an amine dibromide (NHBr ₂ ) and an amine tribromide (NB
r ₃ ), and finally decomposed to N ₂ . Therefore, when the decomposition of NH ₃ is incomplete, ammonia and the above various amine bromide-based substances coexist.

Therefore, when ozone is added in an amount less than the amount required to completely decompose ammoniacal nitrogen into nitrogen gas and the decomposition of ammoniacal nitrogen is incomplete, reducing nitrogen (ammonia) is added to the treated water. Nitrogen and amine bromide-based nitrogen) will always be contained. Therefore, the reducing nitrogen concentration in the treated water was measured, and this concentration was within a certain range,
Specifically, the amount required to completely decompose ammoniacal nitrogen into nitrogen gas by controlling the ozone addition amount so as to be 0.1 to 20 mgN / liter, preferably 0.5 to 5 mgN / liter. It becomes possible to control the ozone addition amount so that a smaller amount of ozone is added to the water.

(C) When adding a smaller amount of ozone than the amount required for completely decomposing ammoniacal nitrogen into nitrogen gas, reducing nitrogen is contained in the treated water, and particularly, the reducing nitrogen concentration is 5 mgN / Below 1 liter, the amine bromides (NH ₂ Br, NHBr ₂ and NBr ₃ ) account for most of the proportion, and below ₂ mg N / liter, most are in the amine form. Since this amine bromide-based substance is toxic, it is necessary to remove it. However, the amine bromide-based substance can be easily decomposed by the action of a catalyst or a reducing agent, and a part of it is decomposed into N ₂ Br ⁻ and the rest NH ₃ and Br ⁻ . The amine bromide-based material can be easily decomposed, especially by a catalyst. Therefore, when an amount of ozone that is less than the amount required to completely decompose ammoniacal nitrogen into nitrogen gas is added, by reacting a catalyst on the treated water in the latter stage of the reaction tank, the amine bromide system in the treated water is reduced. The substance can be easily removed.

(D) NO ₃ ⁻ is a part of NH ₄ ⁺ which is free ammonia (NH ₃ ) in water, and this NH ₃ directly reacts with ozone, or is an intermediate product of the reaction of formula 2. NH
₂ Generated when Br and ozone react with each other. Therefore, when ozone is added in an amount less than the amount required to completely decompose all the amount of ammoniacal nitrogen into nitrogen gas, the amount of ozone added is reduced, and as a result, the amount of NO ₃ ⁻ by-produced is reduced. Moreover, NH ₄ ⁺ from NO ₃ ^- more than route N ₂ is produced from NH ₄ ⁺ is a path generates O ₃ ^-
Therefore, the suppression of the by-production of NO ₃ ⁻ leads to the reduction of ozone consumption, which is economically advantageous.

(E) When a smaller amount of ozone than that required for completely decomposing ammoniacal nitrogen into nitrogen gas is added, a small amount of NH ₃ remains in the water, and this NH ₃ and Br
O ^- and because is NH ₂ Br by reacting the (5) Generation of Br ₂ is less likely to occur by an equation. Therefore, a small amount of remaining NH ₃ is rather preferable.

The present invention has been made on the basis of the findings (a) to (e), and provides the following first to third inventions. (1) First invention In a wastewater treatment method of removing ammoniacal nitrogen in wastewater containing ammonia by adding ozone to the wastewater containing ammoniacal nitrogen in the presence of bromine ions, the ammoniacal nitrogen is completely decomposed into nitrogen gas. A method for treating ammoniacal nitrogen-containing wastewater, which comprises adding ozone in an amount smaller than that necessary for the addition to the ammoniacal nitrogen-containing wastewater.

(2) Second Invention In a wastewater treatment method for removing ammoniacal nitrogen in wastewater containing ammonia nitrogen by adding ozone to the wastewater containing ammoniacal nitrogen in the presence of bromine ions, the treatment after removal of the ammoniacal nitrogen is performed. Reducing nitrogen concentration in water is 0.1-20mgN
A method for treating ammoniacal nitrogen-containing wastewater, which comprises controlling the amount of ozone added to the ammoniacal nitrogen-containing wastewater so that it becomes 1 / liter.

(3) Third Invention In order to discharge the treated water after decomposing the amine bromide substance present in the treated water after removal of ammonia nitrogen into N ₂ and / or NH ₃ and Br ^−. The method for treating wastewater containing ammoniacal nitrogen according to the first invention or the second invention.

The present invention will be described in more detail below. In the first invention, the amount necessary for completely decomposing ammoniacal nitrogen into nitrogen gas (the amount calculated from the above 3 formula)
A smaller amount of ozone is added to the ammoniacal nitrogen-containing wastewater.

The amount of ozone added may be controlled by using the reducing nitrogen concentration in the treated water after removal of ammonia nitrogen as an index, and the reducing nitrogen concentration in the treated water after removal of ammonia nitrogen is 0.1 to 20 mgN. / Liter, preferably 0.
By adding ozone to 5 to 5 mgN / liter, the ozone addition amount can be appropriately controlled (second invention). That is, the reducing nitrogen concentration is 20 m
When it is larger than gN / liter, it can be judged that the ozone addition amount is too small, and when it is smaller than 0.1 mgN / liter, the ozone addition amount is too large. If the reducing nitrogen concentration is less than 0.1 mgN / liter, B
20 mg of Br ₂ may be formed due to residual rO ^−.
If it is more than N / liter, a large amount of ammoniacal nitrogen may remain in the treated water.

In this case, a known ammonia monitor can be used as a means for measuring the reducing nitrogen concentration in the treated water, but a method using a diaphragm type ammonium ion electrode is particularly preferable. The reason is that by using the diaphragm type ammonium ion electrode, not only the concentration of ammonium ions in the treated water but also the total reducing nitrogen (NH ₃ , NH ₂
This is because the concentrations of Br, NHBr ₂ and NBr ₃ ) can be measured, and therefore the above-mentioned control of (b) can be performed accurately. In addition, the amount of ozone added is controlled by
For example, it can be performed by adjusting the flow rate of the ozone-containing gas introduced into the waste water, the ozone concentration in the ozone-containing gas, or the raw water flow rate. In the present invention, the bromine ion-containing water added to the waste water is NaB
An aqueous solution of a bromine compound such as r or KBr or seawater containing a relatively large amount of bromine ions can be used.
Further, the bromine ion concentration in the wastewater at the time of adding ozone is appropriately selected according to the ammoniacal nitrogen concentration in the wastewater, etc., but is usually 1/10 to 10% of the ammoniacal nitrogen content.
It is advisable to double the bromine ion concentration.

In the third invention, the amine bromide-based substance in the treated water after removal of the ammonia nitrogen is N ₂ and / or NH ₃ ,
Dissolve it into Br ^- and discharge the treated water. in this case,
A catalyst is preferably used for decomposing the amine bromide-based substance, which allows the amine bromide-based substance to be easily decomposed. As the catalyst, activated carbon, iron, nickel,
A metal catalyst composed of cobalt, copper or the like can be used. As a means for decomposing the amine bromide-based substance,
In addition, reducing agents such as sulfite and hyposulfite (salt) may be used.

The present invention will be specifically described below with reference to the drawings, but the present invention is not limited to the following examples. FIG.
Shows an example of an apparatus used for carrying out the ammoniacal nitrogen-containing wastewater treatment method of the present invention. In FIG. 1, the same components as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

In this apparatus, a reducing nitrogen measuring means 22 for measuring the reducing nitrogen concentration in the treated water using a diaphragm type ammonium ion electrode is connected to the treated water discharge pipe 20. Further, the control means 24, the ozone-containing gas generator 14, and the reducing nitrogen measuring means 22 are instrumentally connected to each other. Further, the treated water discharge pipe 20 is provided with an amine decomposing means 26 for decomposing the amine bromide-based substance in the treated water by the action of activated carbon, and the exhaust gas discharge pipe 16 is a gas detector for detecting the Br ₂ concentration in the exhaust gas. A pipe 28 is connected.

In the wastewater treatment by this apparatus, the reducing nitrogen measuring means 22 measures the reducing nitrogen concentration in the treated water, and the signal is transmitted to the controlling means 24. The control means 24 controls the ozone-containing gas generator 14 based on the reducing nitrogen concentration, and the ozone-containing gas generator 1
The amount of ozone-containing gas generated in 4 or the ozone concentration in the ozone-containing gas is adjusted. Specifically, the ozone addition amount is controlled so that the reducing nitrogen concentration in the treated water is 0.1 to 20 mgN / liter.

In the apparatus of FIG. 1, the control means 24 controls the ozone-containing gas generator 14 to adjust the ozone addition amount. However, by controlling the flow rate of raw water flowing through the raw water introducing pipe 6. The amount of ozone added can also be adjusted. Further, other configurations may be variously modified without departing from the scope of the present invention.

When the diaphragm type ammonium ion electrode is used as the reducing nitrogen measuring means 22 as described above, the diaphragm of the electrode is deteriorated by the oxidizing power of the amine bromide-based substance in the treated water during long-term use. there is a possibility.
Therefore, when the deterioration of the diaphragm cannot be ignored,
The treated water after removal of ammonia nitrogen to be measured is brought into contact with the above-mentioned decomposition catalyst such as activated carbon, iron, or nickel in advance to decompose the amine bromide-based substance in the treated water, and then the measurement is performed using a diaphragm-type ammonium ion electrode. You may do it. In this case, the concentration of reducible nitrogen measured by the diaphragm type ammonium ion electrode is the amount before the contact treatment by the amount by which a part of the amine bromide-based substance in the treated water is decomposed into N ₂ by the contact with the decomposition catalyst. Although it is lower than water, as shown in the examples below, the amount is usually small, so
Even in such a case, there is almost no problem in practice by controlling the ozone addition amount so that the concentration of reducing nitrogen in the treated water after the decomposition of the amine bromide-based substance becomes 0.1 to 20 mgN / liter.

[0030]

EXAMPLES Next, examples will be shown. An experimental apparatus having the configuration shown in FIG. 1 was produced and the wastewater containing ammoniacal nitrogen was treated under the following conditions. As the ammonia-nitrogen-containing wastewater (raw water), the concentration of ammonia nitrogen in the tap water is 300 mgN
A solution in which NH ₄ Cl was dissolved so that the concentration became / liter was used. As the bromine ion-containing water added to the wastewater, Na
The concentration of NaBr in the wastewater is 130 mg using the Br aqueous solution.
/ Liter (101 mgBr / liter as Br). Ammonium ion measuring device NHMS-3 manufactured by Toa Denpa Co., Ltd. is used as the reducing nitrogen measuring means 22.
It was used. Other conditions are as follows. Reaction tank: capacity 200 liters (height 5 m, inner diameter 22.5
cm) Raw water flow rate: 660 liters / day pH of wastewater in the reaction tank: 6.8

The reducing nitrogen concentration in the treated water is set to 0, 2, 5,
Table 1 shows the results of the wastewater treatment by controlling each to 20 mgN / liter. From Table 1, when the reducing nitrogen concentration in the treated water is 0.1 to 20 mgN / liter, that is, the amount of ozone is less than the amount necessary to completely decompose ammoniacal nitrogen into nitrogen gas, It is recognized that when added to the waste water, Br ₂ in the exhaust gas can be significantly reduced, and NO ₃ ⁻ by-product can be satisfactorily suppressed. On the other hand, when the reducing nitrogen concentration in the treated water is set to zero, excess ozone is added to the ammoniacal nitrogen-containing wastewater in excess of the amount required to completely decompose the ammoniacal nitrogen into nitrogen gas. To
The amount of by-produced Br ₂ and NO ₃ ⁻ was large. Table 1 shows the reducing nitrogen concentration in the treated water after the amine decomposing means 26 decomposed the amine bromide-based substance.
_This corresponds to the amount of the amine bromide substance that became ₂ .

[0032]

[Table 1]

[0033]

In the present invention, since an amount of ozone less than that required for completely decomposing ammoniacal nitrogen into nitrogen gas is added to the ammoniacal nitrogen-containing wastewater, Br ₂ ,
By-production of NO ₃ ⁻ can be suppressed, and the ozone consumption can be reduced. Therefore, there is no need to separately provide a treatment facility for the by-produced Br _{2 in} the exhaust gas line, and it is possible to economically treat the ammoniacal nitrogen-containing wastewater by adding ozone in the presence of bromine ions.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of an apparatus used for carrying out a method for treating wastewater containing ammoniacal nitrogen according to the present invention.

FIG. 2 is a flowchart showing a conventional wastewater treatment apparatus containing ammoniacal nitrogen.

[Explanation of symbols]

 2 Reaction tank 4 Raw water injection device 6 Raw water introduction pipe 8 Bromine ion-containing water introduction pipe 10 Air diffuser, 12 Ozone-containing gas introduction pipe 14 Ozone-containing gas generator 16 Exhaust gas discharge pipe 20 Treated water discharge pipe 22 Reducing nitrogen measuring means 24 Control means 26 Amine decomposition means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuya Uesugi 1-4-9 Kawagishi, Toda City, Saitama Prefecture Organo Research Institute

Claims (3)

[Claims] 1. A wastewater treatment method of removing ammoniacal nitrogen in wastewater containing ammonia by adding ozone to the wastewater containing ammoniacal nitrogen in the presence of bromine ions, whereby the ammoniacal nitrogen is completely decomposed into nitrogen gas. A method for treating wastewater containing ammoniacal nitrogen, comprising adding ozone to the wastewater containing ammoniacal nitrogen in an amount smaller than that required for the wastewater containing ammoniacal nitrogen. 2. A wastewater treatment method for removing ammoniacal nitrogen in wastewater containing ammonia by adding ozone to the wastewater containing ammoniacal nitrogen in the presence of bromine ions. The nitrogen concentration is 0.
A method for treating wastewater containing ammoniacal nitrogen, comprising controlling the amount of ozone added so as to be 1 to 20 mgN / liter. 3. The amine bromide-based substance present in the treated water after removal of ammoniacal nitrogen is N ₂ and / or NH ₃ and Br.
^The method for treating wastewater containing ammonia nitrogen according to claim 1 or 2, wherein the treated water is discharged after being decomposed into-and.