JPH09117782A - Treatment of ammonia-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the total nitrogen concn. by blowing a specified gaseous oxygen into an ammonia-contg. waste water under specified pressurized conditions, bringing the water into contact with a noble metal carrying catalyst under specified heated conditions, then adding hydrogen peroxide and bringing the water into contact with a noble metal carrying catalyst under specified heated conditions. SOLUTION: The ammonia-contg. waste water is sent by a pump 2 from a raw water tank 1 under pressure, and gaseous oxygen having >=90% purity is blown from an oxygen generator 3 into the water at 3-10kg/cm<2> (gage pressure). The water is heated by the remaining heat in a heat exchanger 4, further heated to 140-180 deg.C by a heater 5 and sent to a catalytic reaction tank 6, and the ammonia is removed by the cracking reaction between ammonia and oxygen catalyzed by a noble metal carrying catalyst. Hydrogen peroxide in an amt. more than the equivalent to residual ammonia is added to the treated water leaving the reaction tank 6, and the water is sent to a catalytic reaction tank 7 and brought into contact with a noble metal carrying catalyst at 140-180 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for treating wastewater containing ammonia. More specifically, the present invention provides an ammonia-containing wastewater that can be economically and efficiently advanced treated by treating wastewater containing a high concentration of ammonia to obtain treated water having a total nitrogen of 10 mg / liter or less. Regarding processing method.

[0002]

2. Description of the Related Art Fertilizer factory wastewater, dye factory wastewater, semiconductor factory wastewater and power plant wastewater contain a considerable amount of ammonia. Ammonia is a source of eutrophication in closed waters and must be removed by wastewater treatment. Conventionally known methods for removing ammonia in wastewater include an air oxidation method under high temperature and high pressure, an adsorption treatment method using zeolite, a thermal decomposition treatment method using ammonium nitrite, and a biological nitrification denitrification method. Air oxidation method under high temperature and high pressure is 50kg / cm ²
Blow air into the ammonia-containing wastewater under the above high pressure,
This is a method of decomposing ammonia and removing it as nitrogen gas. Since this method requires high pressure, the equipment is expensive, and there is a drawback that there is a danger of explosion and the reaction vessel is easily corroded. The adsorption treatment method using zeolite is a method of adsorbing and removing the ammonia in the wastewater by the zeolite by utilizing the ion exchange capacity of the zeolite, but at the time of regenerating the zeolite that has reached the ion exchange equilibrium, a high concentration Since the ammonia-containing waste water is discharged, there is a drawback that the treatment is required again. The method of thermally decomposing as ammonium nitrite is a method of adding nitrite to ammonia-containing wastewater to make ammonium nitrite, and then contacting with a noble metal catalyst under heating conditions to decompose and treat as nitrogen gas. In this method, it is necessary to add an equivalent amount of nitrite nitrogen to ammoniacal nitrogen, and ammonia present in the wastewater and an equivalent amount of nitrous acid are required.Therefore, for wastewater containing a high concentration of ammonia, running It has the disadvantage of high cost. The biological nitrification and denitrification method is a method in which ammonia is oxidized to nitrite or nitrate nitrogen by nitrifying bacteria and then reduced to nitrogen gas by denitrifying bacteria. Since this method is a microbial reaction, its decomposition activity is unstable with respect to various fluctuation factors, and the reaction rate is slow and it is necessary to take a long residence time. It has drawbacks such as the need for post-treatment.

[0003]

According to the present invention, there is no generation of by-products that need to be reprocessed, and the process can be carried out by a small reactor so that the total nitrogen concentration in the treated water is 10 mg / liter or less. The purpose of the present invention is to provide an economically advantageous method for treating wastewater containing ammonia.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have succeeded in injecting high purity oxygen gas under pressure into ammonia-containing wastewater to decompose it under heating and catalytic decomposition. Further, they have found that ammonia in waste water can be efficiently treated by adding hydrogen peroxide to treated water and subjecting it to thermal catalytic decomposition, and based on this finding, the present invention has been completed. That is, the present invention provides (1)
Blowing ammonia-containing wastewater with oxygen gas having a purity of 90% or more under a pressurized condition of 3 to 10 kg / cm ² (gauge pressure), 1
After contact with the noble metal-supported catalyst under a heating condition of 40 to 180 ° C., hydrogen peroxide is added to the treated water,
The present invention provides a method for treating ammonia-containing wastewater, which comprises contacting with a precious metal-supported catalyst under a heating condition of 0 ° C. Further, as a preferred embodiment of the present invention,
(2) PSA (Pres
The method for treating wastewater containing ammonia according to item (1), which is oxygen gas separated from the air by the Sure Swing Adsorption method, and (3) the noble metal-supported catalyst carries 0.05 to 10% by weight of platinum on the porous carrier. The method for treating ammonia-containing wastewater according to (1) or (2) above, and (4) the porous carrier having a specific surface area of 10
The treatment method of the ammonia-containing wastewater according to the item (3), which is a titania granular material of -100 m ² / g.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the ammonia-containing wastewater to which the method of the present invention can be applied include wastewater of a dye factory, wastewater of a fertilizer factory, wastewater of a semiconductor factory, wastewater of a power plant, and the like. The method of the present invention is suitable for treating ammonia-containing wastewater containing ammoniacal nitrogen at a high concentration such as 500 to 2,000 mg / liter.
In the method of the present invention, the decomposition of ammonia in the first stage
90% purity under pressure conditions of 3 to 10 kg / cm ² (gauge pressure)
The above oxygen gas was blown into the ammonia-containing wastewater,
It is carried out by contacting with a noble metal-supported catalyst under a heating condition of 0 to 180 ° C. In the method of the present invention, the pressure for blowing oxygen gas is 3 to 10 kg / cm ² (gauge pressure), and more preferably 5 to 10 kg / cm ² (gauge pressure). Conventional air oxidation treatment of ammonia-containing wastewater is usually 50 kg / cm
^Since it is carried out under a high pressure of ² or more, the problems of explosion and corrosion of the reaction vessel were unavoidable. Also, the maximum is 10 kg / cm.
Attempting to perform air oxidation under a low pressure of ² or less was not realistic because the decomposition efficiency of ammonia was poor and the device became extremely large. In the method of the present invention, by blowing oxygen gas having a purity of 90% or more and catalytically decomposing under a heating condition, catalytic oxidative decomposition of ammonia under low pressure becomes possible. In the method of the present invention, oxygen gas having a purity of 90% or more is used. When the purity of oxygen gas is less than 90%, the volume of gas to be blown increases, and the gas volume with respect to the liquid in the reaction tank increases, so that oxygen, liquid and catalyst are
There is a possibility that the contact efficiency of the person will decrease and the decomposition efficiency of ammonia will decrease. The oxygen gas source used in the method of the present invention is not particularly limited, and an oxygen cylinder, liquid oxygen, or the like can be used. However, by providing an oxygen generator of the PSA system, oxygen gas can be easily separated from air. It can be used economically.

In the method of the present invention, the ammonia-containing wastewater in which oxygen gas is blown is contacted with the noble metal-supported catalyst under the heating condition of 140 to 180 ° C. for decomposition. Ammonia reacts with oxygen as in formula (1) to produce nitrogen gas and water. 4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O (1) The reaction is promoted by using the catalyst, and the reaction temperature is 14
It becomes possible to oxidize and decompose ammonia in the temperature range of 0 to 180 ° C. When the temperature of catalytic decomposition is lower than 140 ° C, the decomposition efficiency of ammonia decreases, the reaction time becomes long, and the reaction tank becomes large. When the temperature of catalytic decomposition exceeds 180 ° C., it is necessary to increase the pressure in order to maintain the liquid in the reaction tank in a liquid state, which increases the equipment cost. The noble metal-supported catalyst used in the method of the present invention is not particularly limited, but a catalyst in which a noble metal is supported on a porous carrier can be preferably used. Examples of the noble metal include platinum, ruthenium, palladium, iridium, rhodium, gold, and other noble metals. Among these, platinum is particularly preferable because of its high activity. Examples of the porous carrier include titania, alumina, silica, silica-alumina, and the like, and of these, titania particles can be particularly preferably used. Titania not only has good durability and chemical resistance, but also has a good affinity with ammonia, and attracts ammonia in the vicinity of the catalyst to facilitate the catalytic reaction. The amount of the noble metal supported on the carrier is preferably 0.05 to 10% by weight, and 0.1
It is more preferably ˜1 wt%. If the amount of the noble metal supported on the carrier is less than 0.05% by weight, the catalytic activity necessary for decomposing ammonia may be insufficient. If the amount of the noble metal supported on the carrier exceeds 10% by weight, the cost of the catalyst becomes high and it becomes impractical. The specific surface area of the porous carrier is preferably 10 to 100 m ² / g. If the specific surface area of the porous carrier is less than 10 m ² / g, sufficient catalytic activity may not be obtained. When the specific surface area of the porous carrier is more than 100 m ² / g, the strength of the porous carrier is lowered and the porous carrier may be easily broken. In the method of the present invention, the feed rate to the reaction vessel sparged ammonia-containing waste water the oxygen gas is preferably set to SV0.1～5H ^-1, and more preferably a SV0.5~3h ^-1. If the feed rate is less than SV 0.1 h ^-1 , the reaction time becomes long and the reaction tank becomes large. Supply speed is SV5h ^-1
If it exceeds, the decomposition of ammonia may not proceed sufficiently and the amount of hydrogen peroxide added in the second stage catalytic decomposition may increase. In the method of the present invention, it is preferable to set operating conditions under which 70% or more of the ammonia in the normal wastewater is decomposed and removed by the catalytic cracking by blowing oxygen gas in the first stage.

In the method of the present invention, hydrogen peroxide is added to the treated water which has undergone the catalytic cracking by blowing oxygen gas in the first stage to oxidize and decompose the residual ammonia. Since hydrogen peroxide and ammonia react as in formula (2), the amount of hydrogen peroxide equivalent to the amount of residual ammonia and reaction is calculated, and hydrogen peroxide in excess of that amount is added. 2NH ₃ + 3H ₂ O ₂ → N ₂ + 6H ₂ O (2) In the method of the present invention, the oxidative catalytic decomposition of ammonia with hydrogen peroxide in the second step is carried out by heating the noble metal-supported catalyst under a heating condition of 140 to 180 ° C. This is done by bringing them into contact. The reaction is promoted by using a catalyst, and the reaction temperature is 140 to 1
Oxidative decomposition of ammonia becomes possible in the temperature range of 80 ° C.
When the temperature of catalytic decomposition is lower than 140 ° C, the decomposition efficiency of ammonia decreases, the reaction time becomes long, and the reaction tank becomes large. When the temperature of catalytic decomposition exceeds 180 ° C., it is necessary to increase the pressure in order to maintain the liquid in the reaction tank in a liquid state, which increases the equipment cost. The noble metal-supported catalyst used in the method of the present invention is not particularly limited, but a catalyst in which a noble metal is supported on a porous carrier can be preferably used. Examples of the noble metal include platinum, ruthenium, palladium, iridium, rhodium, gold, and other noble metals. Among these, platinum is particularly preferable because of its high activity. Examples of the porous carrier include titania, alumina, silica, silica-alumina, and the like, and of these, titania particles can be particularly preferably used. Titania is
Not only has good durability and chemical resistance, it also has a good affinity for ammonia and attracts ammonia in the vicinity of the catalyst to make it more susceptible to catalytic reactions. The amount of noble metal loaded on the carrier is 0.
It is preferably from 05 to 10% by weight, more preferably from 0.1 to 1% by weight. If the amount of the noble metal supported on the carrier is less than 0.05% by weight, the catalytic activity necessary for decomposing ammonia may be insufficient. If the amount of the noble metal supported on the carrier exceeds 10% by weight, the cost of the catalyst becomes high and it becomes impractical. The specific surface area of the porous carrier is 1
It is preferably 0 to 100 m ² / g. If the specific surface area of the porous carrier is less than 10 m ² / g, sufficient catalytic activity may not be obtained. When the specific surface area of the porous carrier is more than 100 m ² / g, the strength of the porous carrier is lowered and the porous carrier may be easily broken. In the method of the present invention, the supply rate of the treated water to which hydrogen peroxide is added to the reaction tank is preferably SV1 to 50 h ^−1, and SV5 to
More preferably, it is 30 h ^-1 . Supply speed is SV1
When it is less than h ^-1 , the reaction time becomes long and the reaction tank becomes large. If the supply rate exceeds SV50h ^-1 , the decomposition and removal of ammonia may not be performed completely. In the method of the present invention, the first step of catalytic cracking by blowing oxygen gas and the second step of catalytic cracking by addition of hydrogen peroxide are usually carried out to remove 9% of the ammonia in the first ammonia-containing wastewater.
9% or more is decomposed and removed.

FIG. 1 is a process flow chart of one embodiment of the method of the present invention. Wastewater containing ammonia is pumped from the raw water tank 1 to the pump 2
Is sent by pressure, and oxygen is blown into the waste water from the oxygen generator 3. The waste water is preheated in the heat exchanger 4 by recovering the residual heat, then further heated to a predetermined temperature by the heater 5 and sent to the catalytic reaction tank A6 to remove ammonia by the catalytic decomposition reaction of ammonia and oxygen. . To the treated water flowing out from the catalytic reaction tank A, hydrogen peroxide in an amount equal to or more than the reaction amount of residual ammonia is added and sent to the catalytic reaction tank B7, and the residual ammonia is almost completely removed by the reaction of ammonia and hydrogen peroxide. It The treated water that has left the catalytic reaction tank B is sent to the next step such as pH adjustment after recovering residual heat with a heat exchanger. The method of the present invention, by connecting the catalytic decomposition by oxygen gas and the catalytic decomposition by hydrogen peroxide,
Ammonia is decomposed at a high removal rate even with low-pressure treatment,
It enables efficient treatment of wastewater containing ammonia. Although hydrogen peroxide has a stronger oxidizing power than oxygen and is preferable as an oxidant in terms of performance, it is more expensive than oxygen gas, and the one-step decomposition treatment method using hydrogen peroxide alone is not economical. The method of the present invention removes most of the ammonia with oxygen gas and then removes only the residual ammonia with hydrogen peroxide to keep the amount of hydrogen peroxide used to a small amount and to increase the high oxidizing power of hydrogen peroxide. It can be utilized to reduce the ammonia concentration in the treated water. According to the method of the present invention, ammonia in water can be decomposed and removed into harmless nitrogen gas and water, and by-products that require reprocessing are not generated. Also, by using oxygen necessary for oxidative decomposition of ammonia by separating it from the air by the PSA method, it is possible to easily supply the necessary oxygen on-site. P
When oxygen gas separated by the SA method is used as an oxidant, the cost as an oxidant required for the oxidation of ammonia is generally 1/10 or less of the case of using sodium nitrite,
It becomes 1/20 or less of the case where only hydrogen peroxide is used. In the method of the present invention, since the reaction is promoted by using the noble metal-supported catalyst, the reaction efficiency is increased and the processing apparatus can be downsized. Further, since oxygen gas is used, the amount of gas blown into the target drainage can be theoretically reduced to 1/5 as compared with the case where air is used. Therefore, the contact efficiency between the wastewater to be treated and the catalyst in the catalytic reaction tank is improved.

[0009]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Example 1 Wastewater from a power plant containing 982 mg / liter of ammonia nitrogen and having a pH of 4.9 was treated. In this drainage,
Oxygen gas is blown in 17 liters per 1 liter of drainage (standard condition) under a pressure of 7 kg / cm ² (gauge pressure), 155
After heating to ~ 160 ° C, a catalyst reaction tank filled with 70 ml of a catalyst supporting 0.5% by weight of platinum on a 1.5 mmφ titania carrier (specific surface area 55 m ² / g) is 70 ml / h (SV =
The liquid was passed through at a flow rate of ¹ h ^-1 ). The nitrogen component in the treated water flowing out from the catalytic reaction tank is ammonia nitrogen 220 mg /
Liter, nitrite nitrogen 1 mg / liter, nitrate nitrogen 1
mg / liter or less, total nitrogen 221 mg / liter,
The removal rate of nitrogen by this treatment was 77%. In addition,
The pH of the treated water was 2.1. Then, hydrogen peroxide was added to the treated water to a concentration of 900 mg / liter, and the mixture was heated to 155 to 160 ° C., and then 400 ml / h (SV) was added to the catalytic reaction tank filled with 40 ml of the platinum-supported catalyst.
= 10 h ⁻¹ ). The nitrogen component in the treated water flowing out from the catalytic reaction tank is ammonia nitrogen 1 mg /
Liter, nitrite nitrogen 1 mg / liter, nitrate nitrogen 1
The total nitrogen content was 2 mg / liter or less, and the nitrogen removal rate from the first power plant wastewater was 99.8%. The pH of the treated water was 2.0. From the above results, after the catalytic decomposition of ammonia nitrogen by blowing oxygen gas, the treatment method of the present invention of catalytic decomposition by adding hydrogen peroxide to the treated water, advanced treatment of ammonia-containing wastewater by a small device It was confirmed that it was possible.

[0010]

Industrial Applicability The method of the present invention connects catalytic decomposition of ammonia with oxygen gas and catalytic decomposition of ammonia with hydrogen peroxide, and produces ammonia-containing wastewater with a small device without generation of by-products. Process it efficiently,
Treated water having a low total nitrogen concentration can be used.

[Brief description of the drawings]

FIG. 1 is a process flow chart of one embodiment of the method of the present invention.

[Explanation of symbols]

 1 Raw water tank 2 Pump 3 Oxygen generator 4 Heat exchanger 5 Heater 6 Catalytic reaction tank A 7 Catalytic reaction tank B

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kagawa Corporation 3-3-22 Nakanoshima, Kita-ku, Osaka City Kansai Electric Power Co., Inc. (72) Inventor Tomoyuki Asada 3-3-22 Nakanoshima, Kita-ku, Osaka Kansai Electric Power Co., Ltd. (72) Inventor Toshiji Nakahara 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Kurita Industry Co., Ltd. (72) In-house Yasuhiko Takabayashi 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Kurita Kogyo Kogyo Co., Ltd. (72) Inventor Isao Kou 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Kogyo Co., Ltd.

Claims (1)

[Claims] 1. Ammonia-containing wastewater is 3 to 10 kg / cm.
Oxygen gas with a purity of 90% or more is blown under a pressurized condition of ² (gauge pressure) and brought into contact with a noble metal-supported catalyst under a heating condition of 140 to 180 ° C., and then hydrogen peroxide is added to the treated water, A method for treating ammonia-containing wastewater, which comprises contacting with a noble metal-supported catalyst under heating conditions of 140 to 180 ° C.