JP3203027B2 - Wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for wet-oxidizing wastewater containing chemical compounds requiring oxygen (hereinafter referred to as COD components) and suspended substances in addition to nitrogen compounds in the presence of a solid catalyst. More specifically, by performing wet oxidation of wastewater containing harmful oxidizable organic substances or inorganic substances that are COD components in addition to nitrogen compounds in the presence of an oxygen-containing gas, these substances are converted into harmless carbon dioxide and water. The present invention relates to an effective method for detoxifying wastewater to be converted into nitrogen and the like.

[0002]

2. Description of the Related Art Conventionally, as a wastewater treatment method,
A wet oxidation method called the Mann method is known. This method is a method in which an oxygen-containing gas is supplied to wastewater at high temperature and high pressure to oxidatively decompose organic substances in the wastewater. However, this method has a slow reaction rate and requires a long time to decompose harmful substances. Therefore, methods for using various oxidation catalysts have been proposed for the purpose of increasing the reaction rate.

In the wet oxidation method using this oxidation catalyst, the supply amount of the oxygen-containing gas is generally 1.0 to 1.5 times the theoretical amount required for the decomposition of the wastewater. It was a target.

[0004] However, when wet water containing nitrogen compounds such as cyanide and ammonia is wet-oxidized in the presence of a solid catalyst, oxygen becomes insufficient under the above reaction conditions, so that the catalyst is easily deactivated and the treatment efficiency is reduced with time. There was a problem that the tendency to decrease was recognized, and further, the reactor was easily corroded.

[0005]

Accordingly, an object of the present invention is to efficiently treat wastewater containing nitrogen compounds, particularly wastewater containing nitrogen compounds such as cyanide and ammonia, for a long period of time in the presence of a solid catalyst. It is an object to provide a method.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have found that oxygen-containing gas supplied when performing wet oxidation treatment of wastewater containing nitrogen compounds in the presence of a solid catalyst. It was found that the following excellent effects can be obtained by setting the value of 1.6 to 5.0 times the theoretical oxygen amount.

That is, the present invention relates to a process for wet-oxidizing wastewater containing nitrogen compounds (excluding photographic wastewater ) at a temperature of 370 ° C. or lower and at a pressure at which the wastewater retains a liquid phase. 1.8 to 5.0 of the theoretical amount of oxygen required to oxidatively decompose organic and inorganic substances into nitrogen, carbon dioxide gas and water (hereinafter referred to as "required theoretical oxygen amount").
A wastewater treatment method characterized by wet-oxidizing wastewater using a solid catalyst while supplying a gas containing twice the amount of oxygen.

In the present invention, the supply amount of the oxygen-containing gas is 1.8 to 5.0 times the required theoretical oxygen amount, and preferably 1.8 to 3.0 times the supply gas cost in consideration of the cost. It is. The supply amount of the oxygen-containing gas is required.
If the amount is larger than 0 times, the demerit due to the increase in gas hold-up in the reactor exceeds the efficiency of the above-mentioned reaction rate improvement, so that the processing efficiency tends to decrease rather than 1.6 times the required theoretical oxygen amount. In this case, the surface of the catalyst is always in a state of oxygen deficiency, that is, a reducing atmosphere, and in this state, the processing efficiency tends to decrease.

The solid catalyst according to the present invention includes a catalytically active component element such as manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver, gold, platinum, palladium, rhodium, ruthenium or iridium (hereinafter referred to as catalytic activity). Metal) or a water-insoluble or hardly water-soluble compound such as oxides, chlorides, and sulfides.

These solid catalysts can be used alone, but can be supported on titania, silica, zirconia, alumina, titania-silica, titania-zirconia, activated carbon or diatomaceous earth which are catalyst carriers for wastewater treatment. However, it can also be used as a solid catalyst. When a carrier is used in this manner, the proportion of the carrier in the solid catalyst of the carrier is 75 to 99.95% by weight, preferably 85 to 99.95%.
99.9% by weight, and the catalytically active component is 0.05 to 2%.
It is 5% by weight, preferably 0.1 to 15% by weight. Further, the loading amount of the catalytically active component is 0 to 15% by weight (weight in terms of metal) for elements of manganese, cobalt, nickel, tungsten, copper, cerium, silver or gold, and platinum, palladium, rhodium, The ruthenium and iridium elements are preferably 0 to 5% by weight (weight in terms of metal).

The shape of the solid catalyst may be a pellet, a sphere, a honeycomb, a ring, or the like. In particular, when treating wastewater containing suspended matter, a honeycomb shape is preferable because clogging in the catalyst layer may occur due to solids and precipitates.

As the wet oxidation reactor according to the present invention, a single-tube cylindrical reactor, a multi-tube reactor, or the like is used. If the amount of organic matter contained in the wastewater is large, preheating is required at the start of the reaction. In such a case, it is preferable to use a multitubular reactor.

In order to maintain the liquid phase state of the wastewater, the reaction temperature must be set to a temperature lower than 370 ° C. and higher than the pressure at which the wastewater retains the liquid phase at this temperature.

As the oxygen-containing gas, oxygen alone or one diluted with another gas can be used, but it is preferable to use inexpensive air except in special cases such as downsizing of the apparatus.

The wastewater according to the present invention is wastewater discharged from chemical plants, industrial plants, food factories, etc., and the main components of the wastewater are nitrogen compounds, organic or inorganic substances. Organic substances not containing are aldehydes, alcohols, lower organic acids such as acetic acid and formic acid, and organic compounds containing nitrogen are amine compounds, amide compounds and amino acid compounds. Particularly effective is wastewater containing nitrogen compounds such as cyanide, ammonia, amine compounds, amide compounds and amino acid compounds.

As the amine compound, if it is a compound containing an amino group in the molecule, a primary amine, a secondary amine,
Either a tertiary amine or a quaternary ammonium salt may be used. More specifically, alkylamines such as methylamine, dimethylamine, trimethylamine and propylamine; alkyldiamines such as ethylenediamine and trimethylenediamine; aliphatic amines such as alkanolamines such as ethanolamine and triethanolamine; and aniline And nitrogen-containing heterocyclic compounds such as pyridine and picoline.

An amide compound is a compound having a group (RCONH-) in which an amino group and an acid group are bonded in a molecule. Specifically, formamide, methylformamide, acetamide, ethylformamide, dimethylacetamide, N-acetamide And methylpyrroline.

Amino compounds are compounds having a carboxyl group in the molecule, and include α-amino acids, β-amino acids, and γ-amino acids.
-Amino acids and the like, specifically, aliphatic amino acids such as glycine, alanine, valine, leucine, serine, cysteine, aspartic acid, glutamic acid, lysine, and arginine; amino acids having an aromatic nucleus such as phenylalanine and tyrosine; histidine And amino acids having a heterocyclic ring such as tryptophan and proline.

The above-mentioned nitrogen compounds are not limited to those dissolved in water, but may be suspended or suspended in water. The concentration of these compounds is not particularly limited, but is usually 10 to 100000 ppm.
It is.

The amount of oxygen according to the present invention is 1.8 to 5.0 times the theoretical amount of oxygen necessary for oxidatively decomposing nitrogen compounds, organic and inorganic substances in wastewater into nitrogen, carbon dioxide and water. The present invention is achieved by supplying a gas containing this amount of oxygen. This is because, when wastewater contains nitrogen oxides such as cyanide and ammonia, the decomposition reaction rate is usually high when decomposing using a solid catalyst, so that the oxygen in the wastewater substantially participates in the reaction. When the amount of oxygen that can be consumed is rapidly consumed, and the amount of oxygen is 1.0 to 1.5 times the required theoretical amount of oxygen, the surface of the catalyst is always in an oxygen-deficient state (reducing atmosphere state). This is because the speed decreases and the catalyst is easily deactivated, which tends to reduce the processing efficiency. For this reason, when wet oxidation of wastewater containing cyanide or the like is performed, a gas containing at least 1.8 times the theoretical amount of oxygen is supplied to eliminate the lack of oxygen on the catalyst. the above always becomes oxidizing atmosphere, which is to increase processing efficiency in the oxidation reaction rate is improved. Moreover, it is possible to maintain a stable catalytic activity over a long period of time. Further, when a gas containing oxygen in an amount exceeding 5.0 times the required theoretical oxygen amount is supplied, the temperature of the wastewater associated with the reactor decreases, which is not preferable in terms of reaction efficiency.

It is necessary to set the treatment temperature of the wastewater to a temperature at which the wastewater retains a liquid phase, that is, a temperature lower than a critical temperature.
It is appropriately selected. Hereinafter, specific examples and comparative examples of the present invention will be described, but the present invention is not limited to these examples.

Embodiment 1 FIG. 1 is a schematic view of an apparatus for treating a chemical plant wastewater containing cyanide, ammonia, and the like. The reactor 1 used has an inner diameter of 50 mm, a tube length of 10 m, and a pellet catalyst (Pt having an average particle diameter of 5 mm and a length of 6 mm) inside the tube.
0.5% supported on a titania-zirconia carrier)
Was packed so as to have a catalyst layer length of 8 m.

After the air was pressurized by the compressor 8, the air was mixed with the wastewater supplied from the wastewater supply pump 3, preheated by the heat exchanger 2, and then supplied to the reactor 1.

The wastewater treated in the reactor 1 is supplied to the heat exchanger 2
, And then supplied to the gas-liquid separator 4 where it is separated into harmless gas and water. In the gas-liquid separator 4, the liquid level is detected by the liquid level controller LC, and the liquid level control valve 5 is operated to maintain a constant liquid level.
The pressure is detected by a pressure controller PC, and the pressure control valve 6 is operated to maintain a constant pressure.

The concentration of the wastewater subjected to the treatment is COD (C
r) The content was 30,000 ppm, the cyan concentration was 500 ppm, and the total nitrogen content was 5,000 ppm.

The reaction conditions include a reaction temperature of 250 ° C., a reaction pressure of 70 kg / cm ² G, and a wastewater supply of 30 liters (hereinafter, referred to as “reaction amount”).
L) / Hr, air amount 6 Nm ³ / Hr (twice the required theoretical oxygen amount). As a result, COD (C
r) The processing efficiency was 99%, the nitrogen processing efficiency was 99%, and the cyan concentration was 0.1 ppm or less.

Under the above reaction conditions, even in the continuous operation at 7,000 Hr, no reduction in the treatment efficiency of COD (Cr) and the total nitrogen amount and no change in the cyan concentration were observed.

Example 2 A processing test was performed in which the supplied air amount was four times the required theoretical oxygen amount. The wastewater used for the treatment was the same as the wastewater used in Example 1, and reacted in the same manner as in Example 1 except for the reaction conditions shown below. The reaction conditions include a reaction temperature of 2
50 ° C., reaction pressure 70 kg / cm ² G, wastewater supply 30
L / Hr and air amount was 12 Nm ³ / Hr. As a result, the COD (Cr) treatment efficiency was 99% and the nitrogen treatment efficiency was 99%.
%, The cyan concentration was 0.03 ppm or less. COD even under continuous operation of 7,000Hr under the above reaction conditions
No decrease in the processing efficiency of (Cr) and the total nitrogen amount and no change in the cyan concentration were observed.

Comparative Example 1 A processing test was performed in which the supplied air amount was 1.1 times the required theoretical oxygen amount. The wastewater used for the treatment was the same as the wastewater used in Example 1, except for the reaction conditions shown below.
The reaction was carried out in the same manner as in Example 1. The reaction conditions were a reaction temperature of 250 ° C., a reaction pressure of 70 kg / cm ² G, a wastewater supply amount of 30 L / Hr, and an air amount of 3,300 NL / Hr.
As a result, the COD (Cr) treatment efficiency was 95%, the nitrogen treatment efficiency was 90%, and the cyan concentration was 0.1 ppm. Table 1 shows the change over time in the processing efficiency.

[0030]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a flowchart showing a detailed embodiment for implementing the method of the present invention.

[Explanation of symbols]

 1. Wet reaction tower 2. Heat exchanger 3. 3. Wastewater supply pump Gas-liquid separator 5. Compressor 6. Liquid level control valve 7. Pressure control valve

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-115888 (JP, A) JP-A-2-265696 (JP, A) JP-A 5-119440 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C02F 1/72-1/74

Claims (1)

(57) [Claims] 1. A waste water containing nitrogen compounds (where photo
Excluding the waste liquid ), the nitrogen compounds, organic and inorganic substances in the waste water are oxidized and decomposed into nitrogen, carbon dioxide gas and water when the wet oxidation is performed at a temperature of 370 ° C. or less and the pressure at which the waste water maintains a liquid phase. Wastewater is subjected to wet oxidation using a solid catalyst while supplying a gas containing oxygen in an amount of 1.8 to 5.0 times the theoretical amount of oxygen necessary for the wastewater.