JP3507553B2 - Treatment method for ammoniacal nitrogen-containing water - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating ammoniacal nitrogen-containing water. More specifically, the present invention converts ammoniacal nitrogen in wastewater into harmless nitrogen gas by a catalytic oxidative decomposition method without deteriorating the performance of a noble metal-supported catalyst, and obtains treated water of stable water quality economically and efficiently. To a method for treating ammoniacal nitrogen-containing water. [0002] A considerable amount of ammonia is contained in wastewater from a fertilizer factory, wastewater from a dye factory, wastewater from a semiconductor factory, and the like. As a method for removing ammonia, for example, a biological nitrification denitrification method, Ammonia stripping, chlorine oxidation, catalytic cracking and the like are known. Among these methods for removing ammonia, the biological nitrification 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. However, since this method is a microbial reaction, it has disadvantages such as unstable decomposition activity against various fluctuation factors, a large installation area, and post-treatment of sludge. are doing. Further, the ammonia stripping method is a method in which ammonia is released into the atmosphere by contacting a large amount of air under alkaline conditions. However, this method has a high alkali cost,
In addition, it is necessary to re-adsorb and concentrate the released ammonia, which is not economical. On the other hand, the chlorine oxidation method oxidizes ammonium ions to nitrogen gas via chloramine by adding chlorine. This method requires about 10 times the amount of chlorine added to ammonia, is not suitable for wastewater treatment with a high concentration of ammonia, and requires post-treatment of residual chlorine. In contrast to these methods, the catalytic cracking method has a small installation area of the apparatus, easy operation control, and does not generate substances requiring post-treatment such as sludge and residual chlorine.
For example, Japanese Unexamined Patent Publication No. Hei 4-293553 discloses a method of adding nitrite or nitrite as an oxidizing agent to waste water containing ammoniacal nitrogen, followed by the presence of a noble metal-supported catalyst. A method has been proposed in which ammonia is oxidatively decomposed by heating under heat.
In this method, if the catalytic oxidative decomposition of the ammoniacal nitrogen-containing water is continued, the performance of the noble metal-supported catalyst decreases with the passage of time, so it is necessary to frequently regenerate the catalyst. There is a problem that the performance gradually becomes difficult to recover, and eventually the treatment of the ammoniacal nitrogen-containing water cannot be continued unless the catalyst is replaced with a new noble metal-supported catalyst. for that reason,
There is a demand for the development of a method for treating ammoniacal nitrogen-containing water that can reduce the performance of the noble metal-supported catalyst and stably perform the catalytic decomposition treatment of ammonia for a long period of time. SUMMARY OF THE INVENTION [0003] The present invention is intended to prevent a decrease in catalyst performance, reduce the frequency of regeneration of the catalyst, and improve the efficiency of ammonia nitrogen in the treatment by catalytic oxidative decomposition of ammoniacal nitrogen-containing water. An object of the present invention is to provide a method for treating ammoniacal nitrogen-containing water that can be decomposed well and made harmless, and that can perform a stable treatment operation for a long period of time. Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, in a method for catalytically oxidizing and decomposing ammonia in wastewater containing ammoniacal nitrogen, It has been found that if heavy metal ions present in the wastewater are removed prior to catalytic oxidative decomposition, the performance of the catalyst can be prevented from deteriorating, and treated water of stable water quality can be obtained over a long period of time. Was completed. That is, the present invention provides: (1) a treatment method in which ammonium nitrate or nitrite is added to water containing ammoniacal nitrogen and the ammoniacal nitrogen is converted into nitrogen gas by catalytic oxidative decomposition in the presence of a noble metal-supported catalyst; An object of the present invention is to provide a method for treating ammoniacal nitrogen-containing water, which comprises contacting ammoniacal nitrogen-containing water with a chelating resin before decomposition to remove heavy metal ions in advance. Hereinafter, the present invention will be described in detail. Examples of the ammoniacal nitrogen-containing water to be subjected to the method of the present invention include wastewater from a dye factory, wastewater from a semiconductor factory, and wastewater from a fertilizer factory. In the method of the present invention, the ammoniacal nitrogen in the ammoniacal nitrogen-containing water is treated by catalytic oxidative decomposition. In this case, in order to achieve a stable oxidative decomposition treatment over a long period of time, the noble metal supported catalyst contained in the water to be treated is It is necessary to remove the coexisting substances which affect the performance of the device. As the influence of the coexisting substance on the oxidative decomposition treatment, it is assumed that the coexisting substance is involved in the catalytic reaction itself, a physical influence due to fouling of the catalyst surface, and the like. Coexisting substances that have an adverse effect on such oxidative decomposition treatment include:
For example, heavy metal ions such as iron, copper, zinc, and lead can be mentioned. When, for example, sodium nitrite is added to ammoniacal nitrogen-containing water to perform catalytic oxidative decomposition, a reaction represented by the following formula occurs, and NH ₃ + NaNO ₂ → N ₂ + NaOH + H ₂ O sodium hydroxide is generated and treated. Water becomes alkaline. The amount of sodium hydroxide produced depends on the content of ammonia in the ammoniacal nitrogen-containing water, but usually the pH of the treated water is often 10-12. When the treated water becomes alkaline, heavy metal ions present in the treated water become hydroxides and deposit on the surface of the noble metal-supported catalyst,
This is considered to be the cause of the deterioration of the performance of the catalyst. In the method of the present invention, the ammoniacal nitrogen-containing water is
Prior to the catalytic oxidative decomposition of ammonia, contained heavy metal ions are removed. There is no particular limitation on the method for removing heavy metal ions, and a known method can be used.
Examples include a method in which ammonia-containing water is made alkaline to insolubilize and separate heavy metal ions, a method in which the water is adsorbed to an ion exchange resin, and a method in which the water is adsorbed to a chelate resin. Among these methods, the method of adsorbing to a chelate resin is easy to operate simply by passing the solution through a column filled with a chelate resin, and is preferably used because the chelate resin selectively adsorbs only heavy metal ions. Can be. As the chelate resin, a resin obtained by introducing an iminodiacetic acid group, a polyamine group, or the like into a copolymer of styrene and divinylbenzene can be used. In order to adsorb and remove heavy metal ions in ammoniacal nitrogen-containing water by the chelating resin, for example, the pH of the ammoniacal nitrogen-containing water was adjusted to 1 to 9, preferably 1 to 5, and the chelating resin was filled. In the column, at room temperature, SV = 1
The solution is passed at ５０50 hr ⁻¹ . In the method of the present invention, nitrite or nitrite is added to treated water from which heavy metal ions have been removed by a chelating resin. Alternatively, the order of removal of heavy metal ions and addition of nitrous acid or nitrite is reversed, nitrous acid or nitrite is added to ammoniacal nitrogen-containing water, and then the solution is passed through a column filled with a chelating resin to remove heavy metal ions. Can also be removed. In the method of the present invention, ammoniacal nitrogen-containing water, which is prepared by removing heavy metal ions, adding nitrous acid or nitrite, and adjusting the pH, catalytically decomposes ammonia in the presence of a noble metal catalyst. As the noble metal catalyst, a catalyst in which a noble metal is supported on a carrier is preferable.Examples of the noble metal include platinum, palladium, ruthenium, rhodium, and iridium. Among these, platinum and palladium are particularly preferably used. can do. These noble metals are used in the form of metals, oxides, hydroxides and the like. Examples of the carrier include, for example, α-alumina, γ-alumina, silica, silica alumina, titania, activated carbon, zirconia, zeolite, glass, plastic pellets, ion exchange resin, and the like.
Among them, α-alumina, γ-alumina, titania and the like can be preferably used. The noble metal loading is
It is usually about 0.1 to 10% by weight based on the carrier. There is no particular limitation on the shape of the catalyst, spherical, pellet-like,
Any shape such as powder, granule and the like can be used. Spherical, pellet and granular catalysts can be filled in a column or the like, and water to be treated can be continuously passed through.
A powdery catalyst can also be packed in a column or the like and used in a fluidized bed state. Next, in one embodiment of the method of the present invention, an example in which heavy metal ions are removed using a chelate resin will be described.
This will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an example of an apparatus for performing the method of the present invention. In the method of the present invention, the ammoniacal nitrogen-containing water guided to the raw water tank 1 is
After the pH is adjusted to 1 to 9, preferably 1 to 5, it is sent to the chelating resin packed column 3 by the pump 2. The treated water from which heavy metal ions have been removed by passing through the chelating resin packed tower is sent to the preparation tank 4. In the preparation tank,
0.5 per mole of ammoniacal nitrogen contained in raw water
２2 mol, preferably 0.9-1.1 mol, of nitrite are added. As the nitrite, an alkali metal salt of nitrite such as sodium nitrite and potassium nitrite can be suitably used. If the amount of nitrite or nitrite used is less than 0.5 mole per mole of ammoniacal nitrogen, ammonia in the raw water cannot be sufficiently removed. On the other hand, if the amount of nitrite or nitrite exceeds 2 moles per 1 mole of ammoniacal nitrogen, the amount of nitrite ions remaining in the treated water after removing ammonia is increased, which is not preferable. In the method of the present invention, the pH of the ammoniacal nitrogen-containing water to which the nitrite is added is adjusted by adding an acid or an alkali in a preparation tank, if necessary.
As the acid used for pH adjustment, for example, sulfuric acid or hydrochloric acid can be suitably used. As the alkali used for the pH adjustment, for example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal carbonates such as sodium carbonate and potassium carbonate can be suitably used. In the method of the present invention, the ammonia-containing nitrogen-containing water from which heavy metal ions have been removed, nitrite has been added, and the pH has been adjusted is then sent by a pump 5 to a catalyst packed column 8 packed with a noble metal-supported catalyst. If necessary, in the process of sending to the catalyst packed tower, heat exchanger 6 and heater 7
Ammoniacal nitrogen-containing water can be preheated. In the catalyst packed tower, ammonia reacts with nitrite to form harmless nitrogen gas. The temperature of the catalyst packed tower is 100 to 300
C., preferably at 130 to 180.degree.
If the temperature of the catalyst packed column is lower than 100 ° C., decomposition of ammonia tends to be insufficient even if the contact time is lengthened. On the other hand, if the temperature of the catalyst packed tower exceeds 300 ° C., high pressure resistance is required for the catalyst packed tower and energy is wasted unnecessarily, and the decomposition efficiency of ammonia is not improved. The pressure of the catalyst packed tower is normal pressure to 10
It is preferable to carry out the catalytic cracking reaction at kg / cm ² -G. In the method of the present invention, the total contact time required for the decomposition of ammonia is usually about 3 to 100 minutes, and often about 12 to 30 minutes. SV is usually 0.5 to 20h
r ^-1 , preferably in the range from 2 to 8 hr ^-1 is advantageous. Further, the liquid flow direction of the ammoniacal nitrogen-containing water is preferably an upward flowing liquid. The treated water from which ammonia has been decomposed and removed in the catalyst packed tower is passed through a heat exchanger to a pressure regulating valve 9.
Through to the next processing step. In the method of the present invention, the ammoniacal nitrogen-containing water to be treated is suitably one containing ammonia in the range of 10 to 5000 mg / liter as nitrogen. Wastewater, wastewater from a dye factory, wastewater from a semiconductor factory, and the like. Next, the present invention will be described in more detail by way of examples, which should not be construed as limiting the present invention. Example 1 Ammoniacal nitrogen 2000 mg / l, iron 2.8 mg /
Using ammonia-nitrogen-containing water containing 1 liter and 6.2 mg / liter of copper, catalytic oxidation decomposition of ammonia-nitrogen was carried out by the apparatus shown in FIG. After adjusting the pH of the ammoniacal nitrogen-containing water to 4.1 in the raw water tank, a chelating resin (manufactured by Bayer, Levatit TP-2) was used.
07) at room temperature at SV = 10 hr ^-1 . The content of iron and copper in the treated water flowing out of the chelate resin packed tower was 0.1 mg / liter or less, and these heavy metals had been removed. The treated water from which the heavy metals have been removed is then added with 9860 mg of sodium nitrite per liter of treated water in a conditioning tank, and the pH is adjusted to 6.5 with sodium hydroxide. / Send to a catalyst packed column packed with titania catalyst (average particle size: 1.5 mm), reaction temperature 160 ° C, pressure 9 kg /
The catalytic oxidative decomposition of ammonia was performed with cm ² -Abs, SV = 3 hr ^-1 . The pH of the treated water flowing out of the catalyst packed tower was 10 to 11, and the concentration of ammonia nitrogen in the treated water was stable at 1 mg / liter or less even after the passage of 1000 BV. Comparative Example 1 FIG. 2 is a schematic diagram of an apparatus used in a comparative example. Example 1
Using the same ammoniacal nitrogen-containing water as used in the above, the catalytic oxidative decomposition of ammoniacal nitrogen was carried out by the apparatus of FIG. 2 except for the pump 2, chelating resin packed tower 3 and regulating tank 4 from the apparatus shown in FIG. went. In the raw water tank, 9860 mg of sodium nitrite was added per liter of ammonia-containing water, and sodium hydroxide was added to adjust the pH to 6.5. Then, a 0.5 wt% platinum / titania catalyst (average) was added. (Particle size: 1.5 mm) to a packed catalyst column where the reaction temperature was 160 ° C., the pressure was 9 kg / cm ² -Abs, S
The catalytic oxidative decomposition of ammonia was performed at V = 3 hr ^-1 .
The pH of the treated water flowing out of the catalyst packed tower was 10 to 11, and the concentration of ammonia nitrogen in the treated water was 1 mg / liter or less up to 200 BV.
If it exceeds 0 BV, the concentration of ammonia nitrogen becomes 1 mg / liter or more, and if the liquid is continuously passed, the concentration of ammonia nitrogen in the treated water further increases. Comparing the results of Example 1 and Comparative Example 1, in Example 1 in which iron and copper were removed by treating ammoniacal nitrogen-containing water with a chelating resin, the performance of the platinum-supported catalyst was maintained for a long time. On the other hand, in Comparative Example 2 in which the catalytic oxidative decomposition of ammonia was performed without removing the heavy metal,
The performance of the catalyst is lowered by passing 200 BV. From these results, it can be seen that the life of the noble metal-supported catalyst is prolonged by performing catalytic oxidative decomposition after removing heavy metal ions in the ammoniacal nitrogen-containing water in advance. According to the present invention, by removing heavy metals contained in ammoniacal nitrogen-containing water in advance, it is possible to prevent the deterioration of the catalyst performance due to the deposition of the heavy metals on the catalyst surface, and to greatly improve the stability of the catalyst performance. Therefore, the treatment by the catalytic oxidative decomposition of the ammoniacal nitrogen-containing water can be stably performed over a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an example of an apparatus for performing the method of the present invention. FIG. 2 is a schematic diagram of an apparatus used in a comparative example. [Description of Signs] 1 Raw water tank 2 Pump 3 Chelate resin packed tower 4 Preparation tank 5 Pump 6 Heat exchanger 7 Heater 8 Catalyst packed tower 9 Pressure regulating valve

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Yasuhiko Takabayashi               Chestnut, 3-4-7 Nishi Shinjuku, Shinjuku-ku, Tokyo               Inside Tadano Corporation                (56) References JP-A-4-367784 (JP, A)                 JP-A-59-115786 (JP, A)                 JP-A-5-23678 (JP, A)                 JP-A-7-265876 (JP, A)                 JP-A-58-174235 (JP, A)                 JP-A-56-10388 (JP, A)

Claims (1)

(57) [Claim 1] A treatment in which nitrous acid or nitrite is added to ammoniacal nitrogen-containing water and ammoniacal nitrogen is converted into nitrogen gas by catalytic oxidative decomposition in the presence of a noble metal-supported catalyst. A method for treating ammoniacal nitrogen-containing water, comprising contacting ammoniacal nitrogen-containing water with a chelating resin prior to catalytic oxidative decomposition to remove heavy metal ions in advance.