JPH05169072A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To improve treating efficiency by wet-oxidizing nitrogen containing waste water with a solid catalyst at the prescribed temp. while supplying gas containing oxygen the prescribed times the theoretical oxygen amount required to oxidize and decompose nitrogen compounds, organic substances, etc., included in the nitrogen compound containing waste water. CONSTITUTION:A reactor 1 packed with a pellet catalyst where 0.5% Pt is deposited on a titania-zirconia carrier is used. That is, air 9 from a compressor 5 and waste water 8 from a waste water supply pump 3 are mixed and preheated by a heat exchanger 2 to supply the mixture to the reactor 1 where it is given wet oxidation at a temp. of <=370 deg.C. In this case, pressure is controlled by a pressure control valve 7 operated by a pressure controller Pc so that waste water may be kept liquid phase. The supply amount of air is set so that oxygen 1.6-5.0 times the theoretical oxygen quantity required to decompose the contained nitrogen compounds and organic and inorganic substances into nitrogen, carbon dioxide and water may be supplied.

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 a chemical oxygen demand substance (hereinafter referred to as COD component), a suspended substance and the like in addition to a nitrogen compound in the presence of a solid catalyst. More specifically, by wet-oxidizing wastewater containing a harmful oxidizable organic substance or inorganic substance which is a COD component in addition to a nitrogen compound in the presence of an oxygen-containing gas, these substances are harmless carbon dioxide gas and water. , An effective method for detoxifying wastewater that is converted into nitrogen, etc.

[0002]

2. Description of the Related Art A conventional method for treating wastewater has been
A wet oxidation method called the Mann method is known. This method is a method of supplying oxygen-containing gas to wastewater under high temperature and high pressure to oxidize and decompose organic matter in the wastewater. However, this method has a slow reaction rate and requires a long time to decompose harmful substances. Therefore, a method using various oxidation catalysts has been proposed for the purpose of increasing the reaction rate.

In the wet oxidation method using this oxidation catalyst, the oxygen-containing gas is generally supplied in an amount of 1.0 to 1.5 times the theoretical amount required for the decomposition of waste water. It was target.

However, in the case of wet-oxidizing wastewater containing a nitrogen compound such as cyanogen or ammonia 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 deteriorated over time. There was a problem that the tendency was to decrease, and the reactor was easily corroded.

[0005]

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

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that an oxygen-containing gas to be supplied when a wastewater containing a nitrogen compound is subjected to a wet oxidation treatment in the presence of a solid catalyst. It has been found that the following excellent effects can be obtained by adjusting the amount of oxygen to 1.6 to 5.0 times the theoretical oxygen amount.

That is, according to the present invention, when treating wastewater containing a nitrogen compound, the wastewater is treated in the presence of a solid catalyst.
The theoretical oxygen amount necessary for oxidatively decomposing nitrogen compounds, organic and inorganic substances in the wastewater into nitrogen, carbon dioxide gas and water at a temperature of 370 ° C. or lower and at a pressure at which the wastewater holds a liquid phase (hereinafter, "Required theoretical oxygen amount") 1.6-5.0
A method for treating nitrogen compound-containing wastewater, which comprises performing wet oxidation under the supply of a gas containing a double amount of oxygen.

In the present invention, the supply amount of the oxygen-containing gas is 1.6 to 5.0 times the required theoretical oxygen amount, and considering the cost of the supply gas, it is preferably 1.8 to 3.0 times. Is. When the supply amount of the oxygen-containing gas is more than five times the required theoretical oxygen amount, the demerit due to the increase of gas hold-up in the reactor exceeds the efficiency of the above reaction rate improvement, so the treatment efficiency tends to decrease, This is because when the amount is less than 1.6 times the required theoretical oxygen amount, the surface of the catalyst is always in an oxygen-deficient state, that is, in a reducing atmosphere, and under this state, the treatment efficiency tends to decrease.

The solid catalyst according to the present invention includes manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver, gold, platinum, palladium, rhodium, ruthenium, iridium and other catalytically active component elements (hereinafter referred to as catalytic activity). (Also referred to as a component) or a water-insoluble or sparingly soluble compound thereof, for example, an oxide, a chloride or a sulfide.

This solid catalyst, which can be used alone, is supported on a catalyst carrier for treating wastewater such as titania, silica, zirconia, alumina, titania-silica, titania-zirconia, activated carbon or diatomaceous earth. However, it can also be used as a solid catalyst. When such a carrier is used, the ratio of the carrier to the solid catalyst in the carrier is 75 to 99.95% by weight, preferably 85 to 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 supported amount of the catalytically active component is 0 to 15% by weight (metal equivalent weight) for elements such as 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 (metal equivalent weight).

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

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

In order to maintain the liquid phase state of the waste water, the reaction temperature of the wet oxidation reaction must be set to a temperature of less than 370 ° C., and higher than the pressure at which the waste water holds the liquid phase.

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

The wastewater according to the present invention is wastewater discharged from a chemical plant, an industrial plant, a food factory, etc., and the main components of this wastewater are nitrogen compounds, organic or inorganic substances, such as nitrogen. Organic substances that do not include aldehydes, alcohols, lower organic acids such as acetic acid and formic acid, and organic compounds that include nitrogen include 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, primary amine, secondary amine,
Either a tertiary amine or a quaternary ammonium salt may be used. 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 the like, and nitrogen-containing heterocyclic compounds such as pyridine and picoline.

The amide compound is a compound having a group (RCONH-) in which an amino group and an acid group are bound to each other in the molecule, and specifically, formamide, methylformamide, acetamide, ethylformamide, dimethylacetamide, N- Methylpyrroline and the like.

The amino compound is a compound having a carboxyl group in the molecule, and is α-amino acid, β-amino acid, γ
-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 , Amino acids having a heterocycle such as tryptophan and proline.

The nitrogen compound is not limited to the one dissolved in water, and may be in a suspended or suspended state in water. The concentration of these compounds is not particularly limited, but usually 10 to 100000 ppm
Is.

The amount of oxygen according to the present invention is 1.6 to 5.0 times the theoretical amount of oxygen required for oxidative decomposition of 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 the wastewater contains nitrogen compounds such as cyanogen and ammonia, the decomposition reaction rate is usually high when decomposing using a solid catalyst,
Of the oxygen in the wastewater, oxygen that can be substantially involved in the reaction is rapidly consumed, and when the amount of oxygen is 1.0 to 1.5 times the required theoretical oxygen amount, the surface of the catalyst is always in an oxygen-deficient state (reduction This is because in this state, the oxidation reaction rate decreases and the catalyst is easily deactivated in this state, which tends to reduce the treatment efficiency. For this reason, when wet-oxidizing wastewater containing cyanogen etc., the surface of the catalyst is supplied by supplying a gas containing 1.6 times or more of the theoretical oxygen amount required in order to eliminate oxygen deficiency on the catalyst. The upper part is always in an oxidative atmosphere, which improves the oxidation reaction rate, thereby improving the treatment efficiency and maintaining stable catalytic activity for a long period of time. Further, if a gas containing oxygen in an amount exceeding 5.0 times the required theoretical oxygen amount is supplied, the temperature of waste water relating to the reaction decreases, which is not preferable in terms of reaction efficiency.

The treatment temperature of the wastewater must be set to a temperature at which the wastewater retains a liquid phase, that is, below the seaside temperature.
It is selected appropriately. Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to these examples.

Example 1 FIG. 1 is a schematic view of an apparatus for treating a chemical plant wastewater containing cyan, ammonia and the like. The reactor 1 used had an inner diameter of 50 mm, a tube length of 10 m, and an average particle diameter of 5 mm and a length of 6 mm.
0.5% supported on titania-zirconia carrier)
Was filled so that the catalyst layer length was 8 m.

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

The wastewater treated in the reactor 1 is used as a heat exchanger 2
After being cooled in, it was supplied to the gas-liquid separator 4, where it was 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 controller PC is operated to detect the pressure and operate the pressure control valve 6 to maintain a constant pressure.

The concentration of wastewater used for treatment is COD (C
r) It was 30,000 ppm, cyan concentration was 500 ppm, and total nitrogen amount was 5,000 ppm.

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

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

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

Comparative Example 1 A treatment test was carried out with the supplied air amount being 1.1 times the required theoretical oxygen amount. The waste water used for the treatment was the same as the waste water used in Example 1, except for the reaction conditions shown below.
The reaction was performed 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 waste water 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 treatment efficiency.

[0030]

[Table 1]

[Brief description of drawings]

FIG. 1 is a flow chart showing a detailed mode for carrying out the method of the present invention.

[Explanation of symbols]

 1. Wet reaction tower 2. Heat exchanger 3. Wastewater supply pump 4. Gas-liquid separator 5. Complexer 6. Liquid level control valve 7. Pressure control valve

Claims (1)

[Claims] 1. When wet-oxidizing wastewater containing nitrogen oxides at a temperature of 370 ° C. or lower and at a pressure at which the wastewater maintains a liquid phase, nitrogen compounds, organic and inorganic substances in the wastewater are converted to nitrogen, It is characterized in that the waste water is wet-oxidized by using a solid catalyst under the supply of a gas containing 1.6 to 5.0 times the theoretical oxygen amount necessary for oxidative decomposition into carbon dioxide gas and water. Wastewater treatment method.