JPH04367784A - Treating water containing ammonia - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating ammonia-containing water for removing ammonia from the ammonia-containing water.

0002

BACKGROUND OF THE INVENTION One of the methods for removing ammonia from water is to add nitrous acid or a salt thereof and heat treat it in the absence of a catalyst or in the presence of a catalyst to decompose and remove ammonia.

[0003] This method uses a relatively small device, and
Ammonia can be removed in a relatively short time by simple operations, but the reaction efficiency is poor at low temperatures, and a large amount of ammonia remains in the treated water.

[0004] Therefore, in order to reduce the quality of treated water to 5 mg/l or less as ammonia nitrogen using conventional methods, the reaction must be carried out at a high temperature of 200°C or higher if the reaction is carried out without a catalyst, or about 120°C if a catalyst is used. There is a need to do. For this reason, the decomposition tank requires a pressure-resistant container (pressurized container) that can withstand such conditions, which raises the problem of high cost and danger. Moreover, in the case of no catalyst, the reaction efficiency is poor, the reaction time needs to be lengthened, and the heating section becomes large. When a catalyst is used, there is also the problem that the cost is high due to the cost of the catalyst.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems by removing ammonia safely, efficiently in a short time, and at low cost even under lower temperature conditions than conventional methods. The purpose of this study is to propose a method for treating ammonia-containing water.

[0006]

[Means for Solving the Problems] The present invention provides a thermal decomposition step in which ammonia-containing water is heated and reacted in the presence of nitrous acid or its salt to decompose most of the ammonia into nitrogen gas, and a reaction solution. The process consists of an adsorption step in which the ammonia remaining in the adsorbent is removed by adsorption on the adsorbent, an elution step in which the ammonia adsorbed on the adsorbent is eluted, and a return step in which the eluted eluent is returned to the thermal decomposition step. This is a unique method for treating ammonia-containing water.

In the method of the present invention, the ammonia-containing water to be treated is not particularly limited as long as it contains ammonia;
Water containing ammonia at a relatively high concentration of 0 mg/l or more is suitable for treatment. Specific examples of ammonia-containing water that can be treated by the treatment method of the present invention include ammonium water,
Examples include condensate desalination equipment wastewater discharged from power plants, fertilizer manufacturing wastewater, etc.

Nitrous acid or its salt (hereinafter referred to collectively as nitrous acid (salt)) to be present for the reaction with ammonia-containing water may not need to be added if it already exists. , if the amount is insufficient, add new one. The amount of nitrite (salt) is determined by ammonia-containing water / nitrous acid (
salt) NO2−/NH4+ molar ratio of the mixed solution is 0.5 to 2,
A suitable amount is preferably 1 to 1.1. The pH of the mixture is desirably 0.5 to 5, preferably 0.7 to 4, and can be adjusted to the above range by adjusting the pH if necessary.

The reaction can be carried out in the absence of a catalyst or in the presence of a catalyst, but the reaction efficiency is higher when carried out in the presence of a catalyst. Specific examples of the catalyst include platinum group metals and catalysts in which these metals are supported on carriers such as alumina and zeolite.

[0010] The higher the reaction temperature, the better the efficiency; in the case of no catalyst, the reaction temperature is 120 to 300°C, preferably 140 to 180°C.
, 70-200°C when using a catalyst, preferably 80°C
~99°C is suitable.

In the present invention, in the thermal decomposition step, ammonia-containing water as the water to be treated is heat-treated in the presence of nitrous acid (salt) to thermally decompose ammonia according to the following formula.

[Chemical formula 1] NH4++NO2−→N2+2H2O
… [1]

0012
] Through the above reaction, most of the ammonia in the water to be treated reacts with nitrous acid (salt), decomposes into nitrogen gas, and becomes harmless. At this time, ammonia in the water to be treated is not completely decomposed or removed, and usually 10 to 200 mg of ammonia nitrogen is used.
The reaction is carried out at a temperature at which ammonia remains in an amount of about 20 to 100 mg/l, preferably about 20 to 100 mg/l.

Next, the reaction solution in which ammonia remains is
In the adsorption step, the reaction solution is brought into contact with an adsorbent, and the ammonia remaining in the reaction solution is adsorbed onto the adsorbent and removed. As the adsorbent, those having adsorption properties for ammonia can be used, such as strongly acidic cation exchange resins, weakly acidic cation exchange resins, zeolites, and activated carbon. The adsorption treatment can be carried out by bringing the reaction solution and adsorbent into contact with each other by any method, but it is preferable to pass the reaction solution through a packed bed of adsorbent to bring them into contact. The adsorption treatment reduces the ammonia concentration in the treated water to 5 mg/l or less as ammonia nitrogen, so the treated water can be discharged as is.

[0014] Ammonia adsorbed on the adsorbent is eluted with an eluent in the elution step. Elution of ammonia is preferably carried out when the adsorbent is saturated with ammonia and its adsorption capacity is reduced, but it may be carried out before saturation. As the eluent, sodium sulfate, sodium chloride, sodium nitrite, hydrochloric acid, sulfuric acid, sodium hydroxide, calcium hydroxide, etc. can be used. The concentration of the eluent varies depending on the type, but is generally preferably about 1 to 10% by weight. Elution can be carried out by bringing the adsorbent into contact with the eluent, and when the adsorbent is used in a packed bed, it is preferably carried out by passing the eluent through. The adsorbent from which ammonia has been eluted is used again in the adsorption step.

The ammonia-containing eluent produced in the elution step is returned to the thermal decomposition step in the return step and treated in the same manner as described above. In this case, it is preferable to mix the eluent with ammonia-containing water, which is the water to be treated, and treat it by the thermal decomposition treatment and adsorption treatment, but the eluate alone may be treated.

According to the treatment method of the present invention, since the thermal decomposition step and the adsorption step are combined, the first thermal decomposition treatment can be carried out at a low temperature. Therefore, even in the case of no catalyst, 1
Since the process can be performed at a low temperature of 40 to 180°C, equipment costs and heating costs can be reduced. Furthermore, when a catalyst is used, decomposition can be performed at a temperature of 100° C. or lower, so there is no need to use an expensive pressure-resistant container in the thermal decomposition tank, which reduces equipment costs and heating costs, and is highly safe.

Furthermore, in the present invention, since low concentration ammonia in the reaction solution is concentrated using an adsorbent and returned to thermal decomposition for treatment, ammonia can be efficiently removed. Since ammonia is finally removed in the adsorption step, the ammonia concentration in the treated water becomes low, and high quality treated water with an ammonia nitrogen content of 5 mg/l or less is obtained.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a system diagram showing the processing method of the embodiment. In the figure, 1
2 is a storage tank for water to be treated, 2 is a nitrous acid (salt) storage tank, 3 is a heat treatment tank, 4 and 5 are heat exchangers, 6 is a separator, and 7 is an adsorption tower. The heat treatment tank 3 is filled with a catalyst 8 inside, and a heater 9 is arranged around the outer periphery, so that the entire tank can be heated. The adsorption tower 7 is filled with an adsorbent 10.

In the treatment method, first, water to be treated (ammonia-containing water) 11 is introduced from an ammonia-containing water generation source into a water-to-be-treated storage tank 1 and stored therein. Then, the water to be treated 11 is sent from the water storage tank 1 to be treated by the pump 12, and the aqueous solution of nitrite (salt) 13 is pumped from the nitrous acid (salt) storage tank 2 to the pump 12.
4, and nitrous acid (salt) 13 is added to the water to be treated 11. After this mixed liquid 15 is heated in the heat exchanger 4, it is introduced into the heat treatment tank 3 in an upward flow. In the heat treatment tank 3, the mixed liquid 15 is brought into contact with the catalyst 8 while being heated by the heater 9 to perform heat treatment, and the ammonia in the water to be treated 11 is reacted with nitrous acid (salt) and decomposed into nitrogen gas. . The reaction liquid 16 after the heat treatment is passed through the heat exchanger 4 and mixed liquid 1
5, and further passes through the heat exchanger 5 to cool the water 1.
7 and exhaust gas (nitrogen gas) in separator 6.
It separates into 19 and separation liquid 20.

The separated liquid 20 is introduced into the adsorption tower 7 by a pump 21 and brought into contact with the adsorbent 10, and the ammonia remaining in the separated liquid 20 is adsorbed by the adsorbent 10 to be separated and removed. Treated water 22 is obtained.

When the adsorbent 10 is saturated with ammonia, the introduction of the separated liquid 20 to the adsorption tower 7 is stopped, and the eluent 23 is
is introduced and brought into contact with the adsorbent 10 to elute ammonia. The elution operation is performed in the same manner as the regeneration operation of the adsorbent 10, and the operations of dosing the eluent 23, extrusion, and washing with water are performed in sequence. The eluent 24 generated at this time is introduced into the water to be treated storage tank 1 and mixed with the water to be treated 11, and the heat treatment tank 3 and adsorption tower 7
Process with .

Example 1 Condensate desalination equipment wastewater was used as the water to be treated 11, and the treatment was carried out according to the treatment method shown in FIG. 1 without using the catalyst 8. The processing conditions and results are as follows.

Water quality of treated water 11 pH = 0.7 Ammonia content = 9700 mg/l (as ammonia nitrogen) Thermal decomposition conditions and results Thermal decomposition temperature = 180°C Residence time (HRT) = 20 minutes Sodium nitrite 13 Addition amount = 10000 mg/l (as nitrite nitrogen) reaction solution 1
Ammonia content in 6 (residual ammonia amount) = 50m
g/l (as ammonia nitrogen) Ammonia adsorption conditions and results Type of adsorbent 10 = Strongly acidic cation exchange resin Diamond SK1B [manufactured by Mitsubishi Kasei Corporation, trademark] Packing amount of adsorbent 10 = Bed height 1 m Water LV = 20 m/hr Ammonia content in treated water 22 = 1 mg/l or less (as ammonia nitrogen)

002
4] From the above results, thermal decomposition was performed at 18 without using catalyst 8.
Even when carried out at temperatures as low as 0°C, 1 m of ammonia nitrogen
It can be seen that treated water 22 of less than g/l can be obtained.

When the adsorption capacity of the adsorbent 10 is saturated, the supply of the water 11 to be treated to the adsorption tower 7 is stopped, and a 10% by weight aqueous sodium sulfate solution is added as the eluent 23 to 1 liter of the adsorbent.
Adsorption tower 7 at a rate of 150 g of Na2SO4 per er.
Ammonia was eluted. Then, the adsorbent 10 after elution was used in the same manner as before, and the eluent 24 was further mixed with the water to be treated 11, and ammonia removal treatment was performed in the same manner as above, and the same treatment results as above were obtained. Obtained.

Example 2 The same condensate desalination equipment wastewater as in Example 1 was used as the water to be treated 11, and the treatment was carried out using the catalyst 8 according to the treatment method shown in FIG. The processing conditions and results are as follows. Thermal decomposition conditions and results Thermal decomposition temperature = 99°C Residence time (HRT) = 20 minutes Addition amount of sodium nitrite 13 = 10000 mg/l (as nitrite nitrogen) Catalyst = Ammonia content in platinum-supported alumina catalyst reaction liquid 16 Amount (residual ammonia amount)
= 25 mg/l (as ammonia nitrogen) Ammonia adsorption conditions and results Type of adsorbent 10 = Diaion SK1B adsorbent 1
Filling amount of 0 = bed height 1 m Water flow LV = 20 m/hr Ammonia content in treated water 22 = 1 mg/l or less (as ammonia nitrogen)

002
7] From the above results, even if thermal decomposition is carried out at a low temperature of 99°C, the treated water containing less than 1 mg/l of ammonia nitrogen2
It can be seen that 2 is obtained.

After the above treatment is completed, the separated liquid 20 is transferred to the adsorption tower 7.
The supply of ammonia was stopped, and a 10% by weight aqueous hydrochloric acid solution was introduced into the adsorption tower 7 as an eluent 23 at a rate of 150 g of HCl per liter of adsorbent to elute ammonia. Then, the adsorbent 10 after elution is reused, and the eluent 24 is further reused.
When mixed with the water to be treated 11 and subjected to ammonia removal treatment in the same manner as above, the same treatment results as above were obtained.

[0029]

As described above, according to the present invention, since the treatment is performed by combining the thermal decomposition process and the adsorption process, it is not necessary to completely remove ammonia in the previous thermal decomposition process, and heating can be performed at a lower temperature than before. processing can be carried out, which reduces equipment and heating costs, as well as reducing risks. Moreover, since residual ammonia can be removed in the subsequent adsorption step, treated water of high quality can be obtained. In addition, in the adsorbed ammonia elution process, ammonia can be recovered in a highly concentrated state, and in the return process, it can be returned to the thermal decomposition process with high concentration, resulting in efficient processing. Can be done.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing a processing method according to an embodiment of the present invention.

[Explanation of symbols]

1. Treated water storage tank 2 Nitrite (salt) storage tank 3 Heat treatment tank 4, 5 Heat exchanger 6 Separator 7 Adsorption tower 8. Catalyst 9 Heater 10 Adsorbent 11　Water to be treated 13 Nitrous acid (salt) 15 Mixed liquid 16 Reaction liquid 19 Exhaust gas 20 Separated liquid 22 Treated water 23 Eluent 24 Eluent

Claims (1)

[Claims] Claim 1: A thermal decomposition process in which ammonia-containing water is heated and reacted in the presence of nitrous acid or its salt, and most of the ammonia is decomposed into nitrogen gas, and the ammonia remaining in the reaction solution is removed using an adsorbent. A treatment for ammonia-containing water characterized by comprising an adsorption step in which the ammonia is removed by adsorption on the adsorbent, an elution step in which the ammonia adsorbed on the adsorbent is eluted, and a return step in which the eluted eluate is returned to the thermal decomposition step. Method.