JPH11309467A - Treatment of waste water containing volatile compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of catalytic activity and to execute a stable and efficient treatment over a long period of time by recovering a treated water obtained by removing a volatile compd. by oxidative or reductive decomposition by using an oxidizing agent or a reducing agent generating water or gas by oxidative or reductive decomposition reaction. SOLUTION: The pH of a raw water in a raw water storage tank 1 is subjected to pH adjustment at a pH adjusting tank 2. The pH-adjusted water is sent to a degassing column 5 via a heat exchanger 4 and evaporated and condensed at an evaporating and concentrating device 6 after degassing. The obtained condensed water is moreover concentrated at need, and dried, solidified to dispose. On the other hand, the oxidizing agent (reducing agent) is added to the condensed water at an oxidizing agent (reducing agent) adding tank 7, and the water is passed through a catalyst column 11 via the heat exchanger 9 and a heater 10 to subjected to a catalytic wet oxidation (reduction) treatment. After heat recovering by subjecting the treated water and the treated gas from the catalyst column 11 to heat exchange at the heat exchanger 9, the treated water and the treated gas are subjected to a gas-liq. separation at a gas liq. separating column 13, and the treated water having a good water quality in almost the same order as a distilled water is subjected to a recovery of a waste heat at the heat exchanger 4 and reused.

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 wastewater containing volatile compounds, and more particularly to a method for treating volatile compounds in wastewater by a catalytic wet oxidation / reduction method to prevent a decrease in catalytic performance. The present invention relates to a method capable of performing a stable and effective oxidation / reduction treatment over a long period of time and recovering treated water in a reusable state as distilled water.

[0002]

2. Description of the Related Art As one method of treating wastewater, a catalytic wet oxidation / reduction method in which an oxidizing agent or a reducing agent is added to wastewater in the presence of a catalyst to oxidize or reduce pollutants in the wastewater is known. I have. In this method, after an oxidizing agent or a reducing agent is added to the wastewater to be treated, the wastewater is passed through, for example, a catalyst packed tower and brought into contact with a catalyst to perform oxidation / reduction treatment.

For wastewater containing ammonium ions, the pH of the wastewater is adjusted to around 12 at room temperature to make dissolved ammonia, and then air or steam is blown in to transfer the ammonia into the gaseous phase. There is an ammonia stripping method in which ammonia is decomposed into nitrogen molecules using air or the like as an oxidizing agent in the presence of water.

[0004]

The catalytic wet oxidation / reduction method is a method capable of performing efficient oxidative decomposition or reductive decomposition at a relatively low temperature without problems such as secondary reactions. When the treatment is performed by the wet oxidation / reduction method, the catalyst performance is significantly reduced, and the catalyst life is often short. In some cases, the performance of the deteriorated catalyst can be recovered by the regenerating agent, but in other cases, the catalyst cannot be regenerated, and the catalyst needs to be replaced. In addition, there is a means for previously removing a substance causing a decrease in the performance of the catalyst, but the apparatus configuration is increased and complicated control is required. For this reason, in many cases, the treated water of the target water quality can be obtained only for a short period at the beginning of the passage of water to the catalyst packed tower, and the catalyst needs to be frequently replaced.

[0005] In the treated water obtained by the catalytic wet oxidation / reduction treatment, the substance to be treated is decomposed and removed as gas or water, but substances other than the substance to be treated remain as they are. It is impossible to collect the treated water and reuse it as it is.

[0006] Even in the method in which ammonia is transferred to the gas phase to oxidize the catalyst, the treated water after the removal of ammonia contains salts and the like derived from wastewater, and thus cannot be reused as it is.

[0007] The present invention solves the above-mentioned conventional problems, and prevents a decrease in catalytic activity when treating wastewater containing volatile compounds by a catalytic wet oxidation / reduction method to decompose the volatile compounds. In addition to performing stable and efficient treatment for a long period of time, the treated water obtained by decomposing and removing volatile compounds is recovered as water of the same quality as distilled water, and the treated water can be reused. An object of the present invention is to provide a method for treating wastewater containing a volatile compound.

[0008]

According to the method for treating wastewater containing a volatile compound of the present invention, an oxidizing agent or a reducing agent is added to condensed water containing a volatile compound after evaporating the wastewater containing the volatile compound. A method for treating wastewater containing a volatile compound that oxidizes or reductively decomposes the volatile compound in the presence of a catalyst, wherein the oxidizing agent or the reducing agent generates water or gas by an oxidizing or reductive decomposition reaction. A treated substance obtained by removing the volatile compound by oxidation or reductive decomposition.

The inventors of the present invention have studied the cause of the decrease in catalytic activity in the catalytic wet oxidation / reduction method. As a result, heavy metals, coexisting salts such as F and Cl, and scale-forming substances contained in the wastewater are reduced to It has been found that the active points of the catalyst are blocked by being attached or deposited on the surface of the catalyst, whereby the catalyst is deactivated early.

In the present invention, the wastewater is evaporated, and heavy metals, coexisting salts, scale-generating substances, and the like, which cause a reduction in catalyst performance, remain on the concentrated water (evaporation residue) side.
Most of the volatile compounds to be treated volatilize and migrate into condensed water, so condensed water containing this volatile compound and containing almost no heavy metals or coexisting salts, etc., is subjected to catalytic wet oxidation.
By performing the treatment by the reduction method, it is possible to prevent a decrease in catalyst performance and to stably and efficiently decompose volatile compounds over a long period of time.

Further, in the present invention, since a substance which generates water or gas by an oxidizing or reductive decomposition reaction is used as the oxidizing agent or the reducing agent, the volatile compound is not added to the treated water after the oxidizing or reductive decomposition. The oxidizing agent or reducing agent does not remain as organic substances or salts, and thus the treated water has the same water quality as that of distilled water, and can be recovered and effectively reused as it is.

[0012]

Embodiments of the present invention will be described below.

The wastewater to be treated in the present invention includes volatile compounds such as ammonia, amines, urea, and low-boiling organic compounds such as trichloroethylene.
Wastewater containing organic compounds such as acetic acid and formic acid, volatile compounds such as alcohols, and heavy metals, silica, aluminum compounds and other scale-generating substances, coexisting salts, and the like, which cause a reduction in catalytic performance. Specifically, human wastewater, leachate leachate, semiconductor factory wastewater, dye factory wastewater,
Chemical plant factory wastewater and the like.

In the present invention, such wastewater is first evaporated to obtain condensed water containing a volatile compound. Prior to this evaporation operation, the wastewater is optionally subjected to the classification of the volatile compound contained therein. Accordingly, the volatile compound is likely to evaporate.
Preferably, the pH is adjusted to H. This preferred pH is, for example, pH 8 or less when the volatile compound is ammonia,
In the case of an organic acid, the pH is 5 or less, and in the case of trichloroethylene, the pH is around 7. Further, in the evaporating operation, if gas (for example, oxygen, carbonic acid, etc.) is contained in the wastewater, the thermal efficiency is reduced. Therefore, it is preferable to degas these gases in advance.

The evaporating operation is preferably carried out under such conditions that most of the volatile compounds in the wastewater migrate into the condensed water, and are appropriately determined according to the physical properties (boiling point, etc.) of the volatile compounds and the quality of the wastewater. Is done.

As the evaporation process, a multi-effect evaporation method or a vapor compression evaporation method can be adopted. As the type of the evaporation device, various types such as a natural circulation type, a forced circulation type, a liquid film type and the like can be used. Things can be adopted. Further, a reduced pressure (or vacuum) evaporation method can also be employed.

When the volatile compound is the above-mentioned low-boiling organic compound, it is convenient to boil water at normal pressure.

The condensed water obtained by evaporation contains volatile compounds, while the concentrated water (evaporation residue) concentrates heavy metals, scale-forming substances, coexisting salts such as F and Cl, and the like. You.

In the present invention, the concentration multiple of the concentrated water is appropriately determined according to the quality of the wastewater, but is 2 to 40 times, particularly 5 to 30 times, especially 10 to 20 times, that is, the concentrated water. Capacity is 1/2 to 1/4 of the capacity of the wastewater to be treated
It is preferable to perform the evaporation operation so as to be 0, especially 1/5 to 1/30, especially 10 to 20 times. The condensed water containing the volatile compounds is then brought into contact with the catalyst after adding an oxidizing or reducing agent.

In the present invention, as the oxidizing agent or the reducing agent, a substance that generates water or gas by an oxidizing or reductive decomposition reaction and preferably does not remain as inorganic ions is used. Specifically, air, oxygen, hydrogen peroxide, ozone, or the like can be used as the oxidizing agent. Hydrogen, hydrazine and the like can be used as the reducing agent. The amount of these additions is naturally adjusted according to the type and concentration of the volatile compound.

By using such an oxidizing agent or a reducing agent, the treated water obtained after the catalytic wet oxidation / reduction treatment contains almost no inorganic salts and has a water quality comparable to that of distilled water. Can be reused effectively.

As the catalyst, for example, a heterogeneous catalyst having a metal supported on a carrier is used, and examples of the metal include platinum, palladium, ruthenium, rhodium, iridium, nickel, and cobalt. In addition, as a carrier,
Examples include alumina, titania, activated carbon, zirconia, zeolite, silica, glass, resin, and plastic.

As the contact method, a method in which the condensed water is passed through a column packed with a catalyst is preferable, but other methods may be used. The contact temperature (oxidation or reduction reaction temperature) is generally set in a range from room temperature to 250 ° C., often from 90 to 200 ° C., and is set to a suitable temperature according to the reaction. As described above, since the condensed water does not contain heavy metals, salts, or scale-generating substances that cause a decrease in catalytic performance, the catalytic performance is not hindered by these substances, and the condensed water has a long term. Thus, the volatile compounds can be sufficiently oxidized and reduced.

The concentrated water containing heavy metals, residual volatile compounds, coexisting salts and the like is subjected to coagulation sedimentation filtration, incineration,
It can be processed by solidification. Further, the concentrated water may be subjected to coagulation precipitation filtration, and then the filtrate may be returned to raw water for treatment.

Hereinafter, referring to FIG. 1 showing an embodiment of a method for treating a wastewater containing a volatile compound according to the present invention,
A specific processing procedure will be described.

In the method shown in FIG. 1, raw water (waste water containing volatile compounds) in a raw water storage tank 1 is first added to an acid or alkali, if necessary, in a pH adjustment tank 2 to be suitable for volatilization of the volatile compounds contained therein. Adjust pH to appropriate pH conditions. The pH-adjusted water is sent to the degassing tower 5 via the heat exchanger 4 by the pump 3, degassed in order to prevent a decrease in heat efficiency during evaporation, and then evaporated and condensed in the evaporative concentration device 6. . The concentrated water obtained here is further concentrated if necessary, dried, solidified and disposed.

On the other hand, the condensed water is added with an oxidizing agent (or a reducing agent) in an oxidizing agent (or a reducing agent) adding tank 7 and is passed through a heat exchanger 9 and a heater 10 to a catalyst tower 11 by a pump 8. Then, a catalytic wet oxidation (or reduction) treatment is performed.

The treated water and the treated gas from the catalyst tower 11 are heat-exchanged in the heat exchanger 9 to recover heat, then gas-liquid separated in the gas-liquid separation tower 13, and the treated gas is discharged out of the system. In addition, the treated water is of good quality, almost the same as distilled water,
After the waste heat is further recovered in the heat exchanger 4, it is reused. In addition, at the entrance side of the gas-liquid separation tower 13,
Is provided with a pressure regulating valve 12 for adjusting the pressure to a predetermined pressure, and a decomposition reaction is performed in the catalyst tower 11 by the pressure regulating valve 12 and the heater 10 under predetermined temperature and pressure conditions.

[0029]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 Synthetic wastewater having the following water quality was evaporated under the following conditions using an experimental evaporator equipped with a cooling tube and a heater in a three-necked flask, and then condensed to obtain condensed water having the following water quality.

[Wastewater quality] Ammonia nitrogen: 170 mg / L COD _Mn : 68 mg / L Total dissolved salts: 12000 mg / L Silica: 40 mg / L Cu: 8 mg / L pH: 7.5 [Evaporation conditions] Pressure: normal pressure Temperature: 100 to 105 ° C. Concentration multiple: 10 times [Condensed water quality] Ammonia nitrogen: 154 mg / L COD _Mn : 3.6 mg / L Total dissolved salts: 300 mg / L Silica: <1 mg / L Cu: <1 mg / L pH: 8.5 Hydrogen peroxide (H ₂ O ₂ ) as an oxidizing agent in the above condensed water of the above quality
Was added, and oxidation treatment of ammonia nitrogen was performed in the presence of a catalyst. The reaction between hydrogen peroxide and ammonia nitrogen is represented by the following equation.

2NH ₄ OH + 3H ₂ O ₂ → N ₂ + 8H ₂ O That is, the amount of H ₂ O ₂ required to theoretically oxidize 1 mol of ammonia nitrogen is 3/2 mol.

The processing conditions for the catalytic oxidation were as follows, and the processing method was a catalyst-packed column flow-through method.

[Treatment conditions] Catalyst: 0.5 wt% Pt loading / titania sphere Catalyst filling amount: 50 mL Temperature: 160 ° C. Passing SV: 3 L / hr Passing amount: 1000 BV (50 L) H ₂ O ₂ addition concentration: For ammonia nitrogen molarity,
1.3 times the theoretical addition amount As a result, as described below, treated water having good water quality almost equivalent to distilled water (demineralized water) was obtained.

[Treated water quality] Ammonia nitrogen: 10 mg / L COD _Mn : <1 mg / L Total dissolved salts: <20 mg / L pH: 5.8 Comparative Example 1 In Example 1, oxidation was performed instead of hydrogen peroxide. The treatment was carried out in exactly the same manner except that sodium nitrite (NaNO ₂ ) was used as the agent. The reaction between sodium nitrite and ammonia nitrogen is represented by the following equation, and the reaction produces an equivalent amount of sodium hydroxide in the treated water as ammonia nitrogen.

NH ₄ OH + NaNO ₂ → NaOH + N ₂ + 2H ₂ O As a result, the total dissolved salts of the obtained treated water was 560 mg /
L and pH were 13.5, the salt concentration was high, and further desalting was required for reuse.

COMPARATIVE EXAMPLE 2 The same treatment as in Example 1 was carried out except that the oxidizing agent was directly added to the wastewater without passing through evaporation and condensation, and the mixture was passed through a catalyst packed column. The water quality deteriorated, and the ammonia concentration of the treated water reached 100 mg / L.

[0038]

As is clear from the above Examples and Comparative Examples, according to the present invention, wastewater containing volatile compounds is evaporated and condensed to transfer the volatile compounds to the condensed water side, thereby inhibiting the catalytic performance. After removing the substance, the wet oxidation / reduction treatment of the catalyst is performed, so the wet oxidation / reduction method of the catalyst, which was considered difficult to apply due to the coexistence of the catalytic performance inhibitor in the wastewater, can be applied to various wastewater treatments. This makes it possible to decompose volatile compounds such as ammonia, amine, urea, and trichlorethylene in wastewater stably, effectively and efficiently over a long period of time.

Further, in the present invention, since a substance that generates water or gas by an oxidation or reductive decomposition reaction is used as the oxidizing agent or the reducing agent, the volatile compound is not added to the treated water after the oxidation or reductive decomposition. The oxidizing agent or reducing agent does not remain as organic substances or salts, and thus the treated water has the same water quality as that of distilled water, and can be recovered and effectively reused as it is.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a method for treating wastewater containing a volatile compound according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw water storage tank 2 pH adjustment tank 3, 8 Pump 4, 9 Heat exchanger 5 Degassing tower 6 Evaporation concentrator 7 Oxidizing agent (or reducing agent) addition tank 10 Heater 11 Catalyst tower 12 Pressure regulating valve 13 Gas-liquid separation tower

Claims (1)

[Claims] After evaporating waste water containing a volatile compound, an oxidizing agent or a reducing agent is added to condensed water containing the volatile compound, and the volatile compound is oxidized or decomposed in the presence of a catalyst. A method for treating wastewater containing a volatile compound, wherein the oxidizing agent or the reducing agent is a substance that generates water or a gas by an oxidative or reductive decomposition reaction, and is obtained by removing the volatile compound by an oxidative or reductive decomposition. A method for treating wastewater containing volatile compounds, comprising collecting treated water to be used.