JPH0334996B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for wet oxidizing wastewater containing chemical oxygen demand substances (hereinafter referred to as COD components) in the presence of a catalyst. Specifically, the present invention includes:
By catalytic wet oxidation of wastewater containing harmful oxidizable organic or inorganic substances, which are COD components, in the coexistence of molecular oxygen, these organic substances are converted into harmless carbon dioxide, water, nitrogen, etc. Concerning effective methods to make the world pollution-free.

[Conventional technology]

Known wastewater treatment methods include a biochemical method called the activated sludge method and a wet oxidation method called the Zimmermann method.

As is well known, the activated sludge method requires a long time to decompose organic matter, and it is also necessary to dilute the wastewater to a concentration suitable for the growth of algae and bacteria, so the installed area of the activated sludge treatment facility is large. There are drawbacks to it. Furthermore, in recent years, especially in urban areas, handling of grown surplus sludge requires enormous processing costs. On the other hand, the Zimmerman method uses a pressure of 16 to 200 atm and a temperature of 200 atm for an aqueous solution containing a high concentration of organic matter.
This method introduces air at ~370°C to oxidize and decompose organic matter, but this method requires a large reactor because the reaction rate is slow and decomposition takes a long time, and the material used is highly durable. Because of this, there are economical problems in equipment costs, operating costs, etc. Furthermore, in this method, methods using various oxidation catalysts have been proposed for the purpose of speeding up the reaction rate.

Conventionally, noble metal compounds such as palladium and platinum (JP-A-Show) have been used as catalysts for catalytic wet oxidation
49-44556) and heavy metal compounds such as cobalt and iron (Japanese Unexamined Patent Publication No. 49-94157). These catalysts are catalysts in which the above compound is supported on a spherical or cylindrical carrier such as alumina, silica/alumina, silica gel, or activated carbon. In the case of catalytic wet oxidation of wastewater, the reaction is often carried out at a pH of 9 or above, and according to the study of the present inventors, the above-mentioned catalysts deteriorate in strength and become crushed into powder due to long-term specifications, and furthermore, the catalyst deteriorates. Dissolution may also occur.

Recently, in an attempt to solve these problems, a method using titania or zirconia as a carrier has been proposed (Japanese Patent Laid-Open Publication No. 1988-64188). According to this publication, a catalyst is disclosed in which a noble metal compound such as palladium or platinum, or a heavy metal compound such as iron or cobalt is supported on a spherical or cylindrical titania or zirconia carrier.

On the other hand, there is also a method of oxidatively decomposing organic matter in wastewater at room temperature and under normal pressure using ozone or hydrogen peroxide as an oxidizing agent. For example, in Japanese Patent Application Laid-Open No. 58-55088, wastewater containing organic substances such as humic acid,
A method for oxidatively decomposing the organic substance using ozone and hydrogen peroxide at 20° C. and normal pressure in the absence of a catalyst is described. Also, in Special Publication No. 58-37039,
A surfactant is added to wastewater containing an organic compound having an aromatic ring, and at least one selected from transition metal compounds and alkaline earth compounds is added and mixed, and then this mixture is heated at room temperature and under normal pressure. A method for oxidatively decomposing the organic compound by contacting with ozone is described. Since the former process is carried out in the absence of a catalyst, it is not possible to treat substances that are difficult to oxidize, such as suspended matter in wastewater.
Since the latter uses metal ions such as transition metals or alkaline earth metals as a catalyst, it has the disadvantage of requiring a post-treatment process, as it is necessary to recover the metal ions after treatment of the wastewater rather than releasing them as is. There is. In addition, because both wastewater treatment is carried out at room temperature and pressure, a large amount of expensive ozone is required, the reaction rate is slow, the decomposition rate of organic matter is low, and unreacted ozone is generated. It has drawbacks such as requiring detoxification treatment.

[Problem that the invention seeks to solve]

Therefore, an object of the present invention is to provide an improved method for efficiently oxidatively decomposing organic or inorganic substances contained in wastewater under high temperature and high pressure.

[Means for solving problems]

This purpose is to treat wastewater in the presence of a solid catalyst at 370
1.0 to 1.0 to the theoretical amount of oxygen necessary to decompose organic and inorganic substances in the wastewater into nitrogen, carbon dioxide, and water when the wastewater is treated at a temperature below °C and under a pressure that maintains the liquid phase. This is achieved by a method for treating wastewater characterized by wet oxidation of the wastewater in the coexistence of a gas containing 1.5 times the amount of oxygen and ozone and/or hydrogen peroxide.

The present inventors conducted various studies on oxidizing agents in wastewater treatment methods, and found that when molecular oxygen, ozone, and/or hydrogen peroxide are used as oxidizing agents, they are relatively susceptible to oxidation compared to acetic acid. We discovered that organic substances, which are considered difficult to decompose, can be decomposed with high efficiency, and that the reaction can be carried out at relatively low temperatures and pressures. In the Zimmerman method, which uses molecular oxygen as an oxidizing agent under high temperature and high pressure, no case has been reported to date of the combined use of ozone and/or hydrogen peroxide. Furthermore, since the catalyst used in the present invention has the ability to decompose ozone into oxygen, it also has the advantage of substantially decomposing waste ozone and preventing it from being discharged outside the system. That's true.

In the present invention, the amount of ozone used is 0.001 to 0.001 of the theoretical amount of oxygen required to decompose organic and inorganic substances in wastewater into nitrogen, carbon dioxide, and water.
0.6 times the mole, preferably 0.003 to 0.2 times the mole, is sufficient. Further, the amount of hydrogen peroxide used is 0.001 to 1.8 times the mole of the theoretical oxygen amount, preferably 0.003
~0.2 times the mole is sufficient. By using ozone and/or hydrogen peroxide together with molecular oxygen, the reaction temperature will be higher than when using only molecular oxygen, although it will vary depending on the properties of the wastewater, the amount of the oxidant used, etc. also decreases. For example, the reaction temperature when using molecular oxygen is 200℃.
~300℃, if the oxidizing agent is used together, the temperature will rise to 100℃
The temperature will be ~250℃.

More specifically, preferred reaction conditions for the present invention are as follows: The reaction temperature is usually 370°C or lower, more preferably 100 to 250°C. The pressure of the reaction system is sufficient to maintain the liquid phase of the wastewater in the reaction tower, that is, 0~
A pressure of approximately 200 kg/cm ² is sufficient. The amount of oxygen-containing gas to be fed is 1 to 1.5 times the theoretical amount of oxygen required to decompose organic and inorganic substances in wastewater into nitrogen, carbon dioxide, and water. The amount of solid catalyst used is about 5 to 99% of the space volume of the reaction column. The waste water is oxidized by passing it through a catalyst bed at a predetermined temperature with a residence time of 3 to 120 minutes, preferably 5 to 60 minutes, together with oxygen-containing gas and ozone and/or hydrogen peroxide. The pH of the reaction system can be either acidic or alkaline. As the molecular oxygen-containing gas, air, a mixed gas of oxygen and air, or a gas commonly called oxygen-enriched air can be used, but a gas with an oxygen concentration of 25% or more is preferable.

The present invention can be used to collect supernatant water treated with activated sludge or precipitated activated sludge, fermentation wastewater, wastewater from organic compound polymerization processes, cyanide-containing wastewater, phenol-containing wastewater, oil-containing wastewater, and other chemical factory wastewater as well as from food factories. General industrial wastewater, as well as wastewater containing oxidizable organic or inorganic substances such as human waste, sewage, and sewage sludge, can be subjected to wet oxidation treatment.

In the present invention, any conventionally known wet oxygen catalyst can be used as the solid catalyst. For example, manganese,
A water-insoluble or sparingly soluble compound of at least one element selected from the group consisting of iron, cobalt, nickel, tungsten, copper, cerium, silver, platinum, palladium, rhodium, ruthenium, and iridium in an amount of 0.01 to 50 per catalyst. It is a catalyst supported by weight%. In view of the fact that the present invention carries out the reaction under high temperature and high pressure, it is preferable that the catalyst uses a carrier made of titania, zirconia, or titania-zirconia because the catalyst has excellent durability.

〔Example〕

The present invention will be explained in more detail below using Examples, but the present invention is not limited to these Examples.

Example 1 A composite oxide consisting of titanium and zirconium was prepared by the method described below. A sulfuric acid aqueous solution of titanyl sulfate having the following composition was used as a titanium source.

TiOSO ₄ (TiO ₂ equivalent) 250g / total H ₂ SO ₄ 1100g / 100% water and zirconium oxychloride [ZrOCl ₂ .
8H ₂ O] was dissolved and mixed well while adding 7.7 kg of the above sulfuric acid aqueous solution of titanyl sulfate. While maintaining the temperature at about 30°C and stirring well, ammonia water was gradually added dropwise to the mixture until the pH reached 7, and the mixture was left to stand still for 15 hours.

The thus obtained TiO ₂ -ZrO ₂ gel was filtered, washed with water, and then dried at 200°C for 10 hours. Then, it was fired at 550° C. for 6 hours in an air atmosphere. The composition of the obtained powder was TiO ₂ :ZrO ₂ =4:1 (molar ratio),
The BET surface area was 140 m ² /g. The powder obtained here is hereinafter referred to as TZ-1.

A catalyst was prepared using this powder by the method described below.

900 ml of water, 1500 g of the above powder, and 75 g of starch were added, mixed, and kneaded well using a kneader. After kneading the mixture while adding an appropriate amount of water, it was extruded into a honeycomb mold with a pore diameter (equivalent diameter of the through holes) of 5 mm and a porosity of 64%, dried at 120°C for 6 hours, and the oxygen concentration was reduced to 15%.
% or less at 450° C. for 6 hours.

The thus obtained molded body was immersed in an aqueous palladium nitrate solution and then dried at 120°C for 6 hours.
It was baked at 450°C for 6 hours in an air atmosphere. The composition of the finished catalyst obtained is expressed as a weight percentage: TZ-1:Pd=
It was 97:3.

Example 2 A honeycomb molded body was obtained according to the method described in Example 1 using commercially available titania powder. Next, according to Example 1, except that an aqueous solution of chloroplatinic acid was used instead of an aqueous solution of palladium nitrate,
A catalyst with TiO ₂ :Pt=99:1 was obtained.

Example 3 Using each catalyst obtained in Examples 1 and 2,
Wastewater treatment was carried out using the wet oxidation method as follows. A stainless steel reaction tube is filled with a catalyst, and preheated mixed waste water and gas with an oxygen concentration of 30% and an ozone concentration of 1% are continuously introduced from the bottom of the reaction tube, and the mixture is heated at the inlet and outlet of the reaction tube.
COD (Cr) was measured and the removal rate was determined. The properties of the wastewater used for treatment were COD (Cr) 10g/, and the pH was adjusted to 10 by adding caustic soda. The reaction conditions were a reaction temperature of 190℃, a reaction pressure of 40Kg/ ^cm2 , a space velocity of waste water of 2Hr ^-1 (in the sky column), and a space velocity of oxygen and ozone containing gas of 60Hr ^-1 (in the sky column, standard conditions). introduced into the tube. As a result, when the catalysts of Examples 1 and 2 were used, the COD removal rates were 92% and 91%, respectively.

Example 4 Using the catalyst obtained in Example 1, an oxygen concentration of 30
% and ozone concentration of 1% was introduced into the reaction tube at a space velocity of 60 Hr ^-1 (sky column standard, standard condition), and 3% hydrogen peroxide solution was introduced at a space velocity of 60 Hr -1 (sky column standard, standard condition).
Wastewater was treated in the same manner as in Example 3, except that it was introduced into the reaction tube at a rate of 0.004 Hr ^-1 (empty column standard). As a result, the COD removal rate was 93%.

Claims (1)

[Scope of Claims] 1. When treating wastewater in the presence of a solid catalyst at a temperature of 370°C or less and under a pressure such that the wastewater maintains a liquid phase, organic and inorganic substances in the wastewater are removed by nitrogen, Wastewater characterized by wet oxidation of the wastewater in the coexistence of ozone and/or hydrogen peroxide and a gas containing 1.0 to 1.5 times the theoretical amount of oxygen required to decompose the wastewater into carbon dioxide and water. processing method. 2. The method according to claim 1, wherein the amount of ozone used is 0.001 to 0.6 times the mole of theoretical oxygen required to decompose organic and inorganic substances in wastewater into nitrogen, carbon dioxide, and water. . 3. The method according to claim 1, wherein the amount of hydrogen peroxide used is 0.001 to 1.8 times the mole of theoretical oxygen required to decompose organic and inorganic substances in wastewater into nitrogen, carbon dioxide, and water. Method. 4. The method according to claim 1, wherein the reaction temperature is in the range of 100 to 370°C.