JP3302125B2 - 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 purifying wastewater by wet oxidation treatment. Specifically, chemical plant equipment, plating industrial equipment, leather manufacturing equipment, metal industrial equipment, metal mining equipment, food manufacturing equipment, pharmaceutical manufacturing equipment, textile industrial equipment, pulp and paper industrial equipment, dye and dye industrial equipment, electronic industrial equipment, Regarding the method of purifying wastewater discharged from machine industrial equipment, printing plate making equipment, glass manufacturing equipment, etc. by wet oxidation treatment, high chemical oxygen demand (hereinafter, referred to as
(Hereinafter also referred to as "COD").

[0002]

2. Description of the Related Art Conventionally, an effective treatment capable of purifying wastewater by oxidizing or oxidatively decomposing COD, TOC, nitrogen compounds and the like in wastewater under the conditions of high temperature and high pressure and supply of an oxygen-containing gas. A wet oxidation method has been widely studied as a method. The wet oxidation method converts TOC, COD by converting organic compounds and inorganic compounds of various COD components contained in wastewater into lower molecular weight organic substances, inorganic salts, carbon dioxide gas, nitrogen gas, water and ash. And an excellent wastewater purification method capable of reducing the amount of nitrogen and the like. The treatment liquid treated by this wet oxidation treatment method can be discharged directly to rivers, the sea, and the like. Also, when performing a biological treatment or a chemical treatment as a post-treatment, harmful substances and the like in the wastewater are oxidized or oxidatively decomposed and removed from the wastewater, and the COD components and the like are considerably reduced. Has been decomposed into substances that are very easily decomposed in biological treatment and chemical treatment, so that the burden on the biological treatment equipment or the chemical treatment equipment is very small.

[0003] Further, since wet oxidation treatment equipment is usually operated independently by the heat of oxidation or oxidative decomposition of wastewater generated by the treatment of wastewater, the running cost is lower than that of other wastewater treatment, such as combustion treatment. Is also advantageous.

[0004] However, even in the wet oxidation treatment, which is a very excellent wastewater purification method as described above, due to the characteristics of the treatment, when the treatment temperature is lowered, harmful substances and COD components in the wastewater are reduced. However, there was a problem that the residue remained without being purified. That is, when the treatment temperature cannot be maintained due to the low COD concentration of the wastewater, or when the wet oxidation treatment is stopped, the supply of wastewater having a high COD concentration is changed to the supply of water, and the heat balance is lost. The above-mentioned problem occurs when the temperature decreases.

For this reason, conventionally, a heat supply device such as an electric heater or a steam heater is separately installed, and the processing temperature is maintained by external heating, or the untreated or low-treatment liquid is treated as raw wastewater. Return to the tank etc.
Measures such as processing again have been taken.

In the method of preventing the processing temperature from being lowered by the external heating, it is necessary to separately install the heat supply device, so that the equipment cost is increased, and the entire apparatus is complicated, and the operability and economical efficiency are increased. There was a problem in terms of.

Further, a method of returning the untreated or low-treatment-efficiency treatment liquid to a raw wastewater tank and the like and treating it again involves increasing the amount of treatment liquid, complicating the process at the time of restarting, and increasing the amount of untreated liquid There were problems such as adding tanks for storage or increasing the size of existing tanks.

As another technique, prior to the start of wet oxidation treatment of wastewater, a readily decomposable substance (hereinafter, also referred to as “easy decomposable substance”) and water are reacted by supplying a gas containing oxygen in advance. Supplied into the apparatus, water oxidizes or decomposes easily decomposable substances under pressure to maintain the liquid phase, and the heat generated raises the temperature inside the reaction apparatus to the temperature required for wet oxidation of wastewater Up to
It has been proposed that a wet oxidation reaction can be started promptly. This method is a wastewater treatment technique that can omit or simplify equipment required for preheating at the time of start-up, and that can promptly start an oxidation reaction (Japanese Patent Laid-Open No. 4-300696).

However, this method of treating wastewater is an effective means for initiating a wet oxidation reaction, but purifies wastewater with high treatment efficiency even when the COD concentration of the wastewater to be purified is reduced. The purpose and means of the present technology are different from those of the present technology, which aims to perform wet oxidation treatment continuously and to stop the wet oxidation treatment with high treatment efficiency.

That is, in Japanese Patent Application Laid-Open No. 4-300696, in order to obtain a temperature at which the wet oxidation treatment of wastewater is started, a readily decomposable substance is supplied to a wet oxidation treatment apparatus, and the wet oxidation treatment is started with ordinary wastewater. It is a method of gradually increasing the temperature of the wet oxidizer by starting the wet oxidization process of the easily decomposable substance from a relatively low temperature that cannot be performed. The addition of the easily decomposable substance is started at a temperature lower than the temperature at which the usual wet oxidation treatment is performed.

On the other hand, in the present invention, the temperature at which the easily decomposable substance is added is a relatively high temperature at which wastewater is treated,
It is 50 ° C. or higher, and more generally 230 ° C. or higher, and measures are taken to add a readily decomposable substance to the temperature maintained or maintained. In this case, the purpose is to always treat pollutants such as COD components of wastewater with high treatment efficiency. Thus, what is basically processed is different.

Also, the present invention makes the COD concentration substantially constant by adding a readily decomposable substance even under wet oxidation treatment conditions in which the treatment temperature of waste water, the concentration of waste water, etc. change, and achieves high treatment efficiency of contaminants such as COD components. As a means of treating the wastewater, when the wet oxidation treatment is stopped, the wastewater remaining in the wet oxidation reaction apparatus is not discharged without being treated, and the treatment efficiency is almost the same as when the ordinary wastewater is treated. As a means for treatment, a readily decomposable substance is added to wastewater or water. For this reason, it is necessary to rapidly and highly control the necessary requirements, for example, the amount of the easily decomposable substance to be added with the change of the treatment, and this is also different from JP-A-4-300696.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the temperature required for treatment due to the low COD concentration in the case of purifying pollutants such as harmful substances or COD components in wastewater by wet oxidation. If the wastewater cannot be treated at high efficiency because the water cannot be maintained, or if you want to treat the wastewater supplied when stopping the wet oxidation treatment with high efficiency to the end, add easily decomposable substances and increase the temperature required for treatment. It is an object of the present invention to provide a method for purifying wastewater by a wet oxidation treatment method with an easily decomposable substance, which makes it possible to purify contaminants in wastewater with high efficiency by maintaining the same.

[0014]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies and found that wastewater is subjected to wet oxidation treatment under a pressure of maintaining a liquid phase while supplying a gas containing oxygen. In doing so, it has been found that by adding a readily decomposable substance to wastewater or water and maintaining the treatment temperature at an appropriate wet oxidation treatment temperature of 150 ° C to 370 ° C, wastewater can always be purified with high treatment efficiency. Was completed.

Since the processing temperature is a very important factor in the wet oxidation reaction, it is important to strictly control the processing temperature. Usually, when the treatment temperature is increased, the treatment efficiency of harmful substances or COD components in the wastewater is improved. However, the processing temperature cannot be increased carelessly, and the material of the apparatus, the running cost, and the processing condition range in which the liquid to be processed retains the liquid phase and the wet oxidation processing can be performed must be considered.

Further, when the treatment temperature is lowered, there is a problem that the treatment efficiency of harmful substances or COD components in the wastewater is reduced. Therefore, the present invention maintains the treatment temperature at an appropriate wet oxidation treatment temperature of 150 ° C. to 370 ° C. when the waste water is subjected to wet oxidation treatment under a pressure that maintains a liquid phase under the supply of an oxygen-containing gas. In order to achieve this, an easily decomposable substance is added to wastewater or water in an appropriate amount, and the liquid is subjected to wet oxidation treatment to obtain heat from the inside to maintain and control the treatment temperature, thereby setting the treatment temperature to the optimum temperature. Adopt a method of maintaining. It is an object of the present invention to provide a wastewater treatment method which is extremely simple and inexpensive in terms of equipment and which is easy to operate and which is excellent in practicality and economic efficiency, as compared with the above-mentioned conventional method. That is, the present invention is specified as follows.

[0017]

(1) Under the supply of a gas containing oxygen, 15
At a temperature of 0 ° C. to 370 ° C., the waste water is supplied to a wet oxidation treatment apparatus under a pressure at which the waste water retains a liquid phase, and the wet oxidation treatment operation is stopped in the waste water treatment method of wet oxidation treatment.
When stopping, it is easy to supply wastewater to wet oxidation treatment equipment.
Switch to water containing degradable substances, and continue to use only water
A method for treating wastewater, wherein the wet oxidation treatment is stopped after switching to supply of wastewater.

[0019]

(2) The method for treating wastewater according to the above (1) , wherein the wet oxidation treatment device is a wet oxidation treatment device using a catalyst.

[0021]

The present invention is not particularly limited as long as the treatment temperature is increased and a readily decomposable substance is added for the purpose of always treating harmful substances or COD components in wastewater with high treatment efficiency. In order to prevent a decrease in the treatment temperature due to a low COD concentration of the wastewater during the wet oxidation treatment of the wastewater, or to stop the wet oxidation treatment apparatus, an insufficiently treated wastewater component is removed. Implement to prevent discharge.

The easily decomposable substance in the present invention is not particularly limited as long as it is very easily decomposed in a wet oxidation treatment (also referred to as “easy decomposability”) and does not generate a secondary pollutant after the treatment. However, for example, lower alcohols such as methanol, ethanol, and isopropanol; lower organic acids such as formic acid and acetic acid; lower aldehydes such as acetaldehyde and formaldehyde; sucrose; sugars such as glucose; lower such as acetone and methyl ethyl ketone. Ketones and other inorganic substances such as sodium thiosulfate and sodium sulfide can be mentioned. Among them, methanol is particularly effective because of good handleability, economic efficiency and good treatment efficiency in wet oxidation treatment. The easily decomposable substance does not need to be a single substance, and may be a mixture of several kinds, or other wastewater which is easily decomposed by a very wet oxidation treatment, and is not particularly limited. In addition, it is effective that the easily decomposable substance and the secondary products generated by the wet oxidation treatment of the easily decomposable substance are easily treated in biological treatment.

In the present invention, the liquid containing a readily decomposable substance includes a liquid containing a readily decomposable substance, a liquid which is easily treated in a wet oxidation treatment, and a liquid which contains an easily decomposable substance. Liquids containing easily decomposable substances added to water, and liquids containing easily decomposable substances added to water, and liquids containing easily decomposable substances added to wastewater. The liquid that can be easily treated may be wastewater discharged from another plant or the like, and is not particularly limited.

The method for adding the easily decomposable substance in the present invention is not particularly limited. For example, when the COD concentration of waste water is low and the present invention is carried out, only the easily decomposable substance or the easily decomposable substance dissolved in water may be used. The liquid to which the substance has been added may be supplied directly to the wet oxidation treatment apparatus using a pump, or a readily decomposable substance may be added to a wastewater tank and supplied together with the wastewater (hereinafter referred to as water or wastewater). And a solution obtained by mixing the easily decomposable substance with the “decomposable liquid after addition”. Further, when the present invention is implemented to stop the wet oxidation treatment apparatus, after stopping the supply of the wastewater, the easily decomposable substance dissolved in the water may be supplied by the same pump as the supply of the wastewater,
The easily decomposable substance and water may be supplied using separate pumps. When supplying easily decomposable substances to the wet oxidation treatment device using a pump that supplies wastewater and another pump,
The position is not particularly limited as long as it is in front of the reaction tower or the reaction tower.

The present invention is not particularly limited by the type of wastewater to be subjected to wet oxidation treatment, but can be applied to any wastewater as long as it is wet oxidation treatment. That is, the present invention can be applied to general wastewater containing only organic substances, wastewater containing sulfur compounds, wastewater containing nitrogen compounds, wastewater containing inorganic compounds, wastewater containing suspended matters, and the like.

In the present invention, the COD (Cr) concentration of the wastewater when the ordinary wastewater before the addition of the easily decomposable substance is stably treated by wet oxidation is not particularly limited. 5 g / l to 120 g / l is effective, and more effective is 10 g / l to 80 g / l.

When the present invention is carried out in order to prevent a decrease in the treatment temperature due to a low COD (Cr) concentration of the wastewater, the period for carrying out the present invention, that is, the period for adding the readily decomposable substance is not particularly limited. In addition, the method of the present invention provides a short-term COD
It is particularly effective as a measure to reduce the (Cr) concentration, etc. In many cases, a method of providing a countermeasure is economically excellent, and in consideration of these points, the period in which the present invention can exert an effect is preferably a period of less than 40% of the period during which the wet oxidation treatment is performed. Preferably, the period is less than 20%. If the period exceeds 40%, the cost of easily decomposable substances increases, which is economically disadvantageous.

When the present invention is implemented to prevent a decrease in the treatment temperature due to a low COD (Cr) concentration of the wastewater, the present invention may be implemented after detecting that the treatment temperature of the wastewater cannot be maintained. Good, but before processing temperature falls,
Detecting the change in OD (Cr) concentration and implementing the present invention is very effective because various processing efficiencies do not decrease. The detection method for this purpose is not particularly limited, and a method in which the COD (Cr) concentration of the wastewater stock solution is measured in advance before the wet oxidation treatment is preferable.

When the oxygen-containing gas used in the wet oxidation treatment is supplied at a constant amount, it can be predicted by measuring the amount of residual oxygen in the exhaust gas after the treatment.
It can be predicted from various methods such as a change in the properties of the processing solution after the processing, and the present invention is not particularly limited by the detection method. However, even if the COD (Cr) concentration of wastewater is reduced during wet oxidation treatment by adopting the above detection methods, etc., easily decomposable substances to maintain the treatment temperature and maintain high treatment efficiency It can be added in advance and is important in the present invention.

Usually, the reason why it is necessary to carry out the present invention in order to prevent a decrease in the treatment temperature during the wet oxidation treatment of wastewater is often due to a decrease in the COD (Cr) concentration of the wastewater. However, the present invention is not particularly limited to this, and the present invention can also be applied to a case where the composition of the wastewater changes and the amount of heat generated due to a decrease in the COD (Cr) treatment efficiency or the like becomes insufficient and the treatment temperature decreases. In addition, the present invention can be applied to a case where a decrease in the wet oxidation treatment temperature in a case where an increase in the amount of heat radiation due to a defect in the heat insulating material of the apparatus or an increase in the amount of heat radiation due to a change in weather conditions is prevented.

Since the COD (Cr) concentration of the wastewater is low, the present invention can prevent the increase of the COD (Cr) concentration of the wastewater and the excessive addition of easily decomposable substances. For this purpose, it is more effective to detect the COD (Cr) concentration change of the wastewater in advance and implement the present invention. Although the detection method for this is not particularly limited,
As in the above case, a method in which the COD (Cr) concentration of the undiluted wastewater is measured in advance before the wet oxidation treatment is preferable. When the oxygen-containing gas used in the wet oxidation treatment is supplied in a constant amount, it can be predicted by measuring the amount of residual oxygen in the exhaust gas after the treatment. In addition, it can be predicted from various methods such as a change in the properties of the treatment liquid after the treatment, and a suitable detection method can be appropriately adopted as long as it does not contradict the spirit of the present invention.

When the easily decomposable substance of the present invention is added in order to prevent that the harmful substances or COD components in the waste water cannot be treated with high efficiency due to a decrease in the treatment temperature, the COD (Cr) concentration of the waste water is reduced. Although not particularly limited, the COD (Cr) concentration is 10% to 70% higher than the COD (Cr) concentration at which wastewater is usually wet-oxidized by a wet-oxidation treatment apparatus.
It is effective when the COD (Cr) concentration is reduced, and more effective when the COD (Cr) concentration is reduced by 20% to 50%.
If it is less than 10%, the processing temperature is less likely to decrease,
According to the present invention, it can be sufficiently treated without adding the easily decomposable substance, and does not bring about the excellent effect of the present invention. Requires a large amount of an easily decomposable substance to be treated, which increases wastewater treatment costs, which is not preferred.

The amount of the easily decomposable substance to be added is not particularly limited, and an amount of the easily decomposable substance that suppresses a decrease in the processing temperature may be added. From the above, the amount of the easily decomposable substance added is the COD (Cr) of only the easily decomposable substance in the additive solution.
The concentration is effective in the range of 0.5 g / l to 100 g / l, and more effectively in the range of 2 g / l to 5 g / l.
0 g / liter.

When the present invention is carried out in order to stop the wet oxidation treatment apparatus, the supply amount of the liquid after the addition of the easily decomposable substance is not particularly limited, but the waste water remaining in the reaction apparatus is treated. It is preferable to supply the treatment liquid to the extent that the amount of harmful substances and the like contained in the treatment liquid is reduced. Although it is not particularly limited, 0.5 times the capacity of the reaction tower is not specifically limited.
More than twice and less than 10 times is effective, and more effectively 1 times or more and less than 5 times. When the ratio is less than 0.5 times, the effect of the present invention is reduced, and harmful substances of wastewater components often remain in the treatment liquid. When the ratio is 10 times or more, easily decomposable substances Requires a large amount of liquid, which is not preferable in terms of cost, and it takes a long time to stop the operation, and the amount of liquid increases.

When the present invention is carried out to stop the wet oxidation treatment apparatus, the supply of wastewater is stopped, and the temperature of the wet oxidation reaction tower or the heat exchanger is reduced when supplying the liquid after adding the easily decomposable substance. The supply amount of the easily decomposable substance may be appropriately adjusted while monitoring the water content. However, in order to stabilize the treatment temperature, for example, the COD (Cr) concentration of the wastewater before stopping the wastewater supply and the COD It is better to measure the (Cr) concentration and adjust the COD (Cr) concentration of the solution after adding the easily decomposable substance so that it is almost equal to the COD (Cr) concentration of the wastewater purified. It is possible to obtain a stable processing temperature without lowering the efficiency and the like, and to enhance the purifying property of the discharged processing liquid. In addition to the COD (Cr) concentration of the wastewater before the stoppage of the wastewater supply and the COD (Cr) concentration of the treatment liquid, a method of measuring the residual oxygen concentration in the exhaust gas during the wastewater treatment and calculating from the consumed oxygen amount Alternatively, it can also be calculated from an analysis of changes in properties such as the composition of the wastewater and the composition of the treatment liquid, and the present invention is not particularly limited by these methods. However, by adopting the various methods described above, the supply amount of the easily decomposable substance and the like are adjusted in advance so that the treatment temperature does not change when the supply of the liquid to the liquid after the addition of the easily decomposable substance is switched from the stoppage of the wastewater. It is also an important point in the present invention that the method for stopping the wet oxidation treatment according to the present invention can maintain a very high treatment liquid purifying property.

In the present invention, the amount of the easily decomposable substance is
The amount is not particularly limited as long as the temperature required for performing the wet oxidation treatment of the wastewater can be maintained. That is, when the present invention is implemented to prevent a decrease in the treatment temperature due to a low COD (Cr) concentration of the wastewater, etc., when the COD (Cr) treatment efficiency of the wastewater is high, the wet oxidation treatment is usually performed. COD of wastewater
(Cr) concentration and COD of the liquid after addition of the easily decomposable substance of the present invention (Cr)
A readily decomposable substance is added so that the concentrations are almost equal.
When the COD (Cr) treatment efficiency of the wastewater is low, the COD (Cr) concentration difference between the COD (Cr) concentration of the wastewater that is usually subjected to wet oxidation treatment and the COD (Cr) concentration of the wastewater that implements the present invention is reduced. An easily decomposable substance having a COD (Cr) concentration substantially equal to the COD (Cr) concentration obtained by multiplying the COD (Cr) treatment efficiency in ordinary wet oxidation treatment is added. The reason for this is to make the amount of heat generated when the wastewater is subjected to the wet oxidation treatment substantially equal. While the easily decomposable substance is decomposed almost 100% in the practice of the present invention, the wastewater is generally 100% decomposed. % In many cases, and if the easily decomposable substance is added so as to have the same COD (Cr) concentration, the amount of generated heat may be excessive.

Similarly, when the present invention is carried out in order to stop the wet oxidation treatment apparatus, the supply amount of the waste water when the waste water is being subjected to the wet oxidation treatment and the liquid after addition of the easily decomposable substance switched for the stoppage. When the COD (Cr) treatment efficiency of the wastewater is high, the COD (Cr) concentration of the wastewater which is usually subjected to wet oxidation treatment and the liquid after addition of the easily decomposable substance of the present invention under the condition that the supply amount of A readily decomposable substance is added so that the COD (Cr) concentration of the above becomes substantially equal. When the COD (Cr) treatment efficiency of wastewater is low, CO
The COD (C) concentration is approximately equal to the COD (Cr) concentration obtained by multiplying the D (Cr) concentration by the COD (Cr) treatment efficiency in a normal wet oxidation treatment.
r) Add a concentration of readily degradable substance.

The cases where the COD (Cr) treatment efficiency is high and the case where the COD (Cr) treatment efficiency is low are defined as the wet oxidation treatment apparatus and treatment conditions for implementing the present invention,
The composition of the wastewater to be treated is different from each other and is not particularly limited. In each case, the COD (Cr) treatment efficiency in which the present invention can be satisfactorily implemented without considering the COD (Cr) treatment efficiency of the wastewater is a case where the COD (Cr) treatment efficiency described here is high, Conversely, COD
If the COD (Cr) processing efficiency is such that the present invention cannot be carried out well without considering the (Cr) processing efficiency,
This is the case where the OD (Cr) processing efficiency is low. For example, COD (C
r) When the processing efficiency is 90% or more, the COD (Cr) processing efficiency does not need to be considered, and when the processing efficiency is less than 90%, COD (C
r) It is often necessary to consider processing efficiency.

An ordinary wet oxidation treatment apparatus is designed with a COD (Cr) concentration of 5 g / l to 150 g / l, and more often 10 g / l to 100 g / l.
Liters. For this reason, the CO
The D (Cr) concentration is effective at 5 g / L to 120 g / L, and more effectively at 10 g / L to 80 g / L.
g / liter. In this case, the COD (Cr)
The concentration is a concentration after the easily decomposable substance is mixed with the wastewater or water, and is different from the concentration of the pump supply liquid for supplying the easily decomposable substance.

The space velocity of the wet oxidation treatment of the liquid to which the easily decomposable substance is added in the present invention is not particularly limited, but the space velocity of the wastewater before the addition of the easily decomposable substance and the space velocity after the addition of the easily decomposable substance It is effective to make the space velocity of the liquid the same. Changing the space velocity requires complicated operations, and changes the efficiency of treating harmful substances or COD components in wastewater. Specifically, it is effective at a space velocity of 0.1 hr to ¹ to ¹⁰ hr to ¹ , which is equivalent to the space velocity of general wet oxidation treatment of wastewater,
More effectively, it is 0.5 hr- ¹ to ⁵ hr- ¹ . Generally, when the space velocity exceeds 10 hr- ¹ , the processing efficiency is reduced, and when the space velocity is less than 0.1 hr- ¹ , the processing speed is reduced, and it takes too much time, which is not preferable. is there.

The space velocity of this wet oxidation treatment and COD (Cr)
There is a correlation between concentration and processing temperature. There are two main causes of the decrease in the processing temperature of a general wet oxidation apparatus.

One is a decrease in the amount of heat due to heat radiation from the reaction tower, the heat exchanger and the like, and the other is a decrease in the amount of heat due to the heat exchange loss in the heat exchanger. If the amount of heat corresponding to the decrease in the amount of heat is supplied by the heat of oxidation or oxidative decomposition of the COD component by wet oxidation, stable processing can be performed. That is, the product of the supply amount of the COD component-containing liquid and the COD concentration is proportional to the supplied heat amount, and the processing temperature is proportional to the supplied heat amount.

The processing pressure of the wet oxidation treatment of the present invention is appropriately selected depending on the correlation with the processing temperature, and is determined by the pressure at which the liquid maintains a liquid phase.

The treatment temperature of the wet oxidation treatment of the present invention is 15
0 ° C or higher and lower than 370 ° C, preferably 200 ° C or higher and lower than 300 ° C, more preferably 230 ° C or higher and 2 ° C or lower.
It is less than 80 ° C. When the temperature is 370 ° C. or higher, the liquid cannot maintain a liquid phase. If the temperature is lower than 150 ° C., the wastewater subjected to the wet oxidation treatment itself is often an easily decomposable substance that can be very easily treated, and the effect of the present invention cannot be expected much. Further, when the temperature is lower than 200 ° C., the conventional method using an external heater using an electric heater or a steam heater or the like may be relatively easily implemented, and this is an area where the advantages of the present invention are relatively small. .

In the present invention, the temperature of the wet oxidation treatment of the liquid containing the easily decomposable substance is a temperature which is not lower than the temperature of the wet oxidation treatment in which the waste water is subjected to the wet oxidation treatment in a stable state by 20 ° C. or more. The temperature is preferably not lower than 10 ° C, more preferably not lower than 5 ° C. If the wastewater is wet-oxidized and the temperature is 20 ° C. or more lower than the stable wet-oxidation treatment temperature, the effect of the present invention is reduced, and harmful substances of wastewater components, COD components, etc. May be discharged with insufficient treatment.

In the present invention, the temperature of the wet oxidation treatment of the liquid containing the easily decomposable substance is a temperature which is not higher than the temperature of the wet oxidation treatment in which the wastewater is subjected to the wet oxidation treatment in a stable treatment state by 30 ° C. or more. , Preferably a temperature not higher than 20 ° C, more preferably a temperature not higher than 10 ° C. When the wet oxidation treatment is performed only with the wastewater and the temperature is 30 ° C. or more higher than the wet oxidation treatment temperature at which the stable treatment has been performed, the treatment efficiency of the wastewater and the treatment efficiency and the wastewater treatment temperature are higher than the normal wet oxidation treatment temperature. Although the purification performance may be higher, it is often the case that the temperature is higher than the design temperature of the wet oxidation treatment equipment, and the processing pressure is changed to a higher processing pressure so that the liquid retains the liquid phase in order to obtain a higher processing temperature. There are many things you need to do. For this reason, not only is the facility impossible in many cases, but also the operating cost and the like are increased, and the wastewater is usually excessively treated as compared with the case where the wet oxidation treatment is performed.

That is, in the present invention, the temperature of the wet oxidation treatment of the liquid to which the easily decomposable substance is added is substantially equal to the temperature of the wet oxidation treatment that has been carried out by the wet oxidation treatment only with the wastewater and the stable treatment. It is the most effective in terms of performance, equipment and cost.

In the present invention, the oxygen-containing gas means a gas containing oxygen or ozone. When a gas such as ozone or oxygen is used, it can be appropriately diluted with an inert gas or the like before use. Preferably air is used,
In addition to these gases, oxygen-containing waste gas generated from other plants can be used as appropriate.

The amount of the gas used can be appropriately selected depending on the concentration of the wastewater. In this case, the amount of oxygen required to completely convert the COD component of the wastewater to water, carbon dioxide, inorganic salts, other ash, and the like is 0.5 to 5 times, and more preferably 1 to 5 times.
It is twice. Unnecessary supply of oxygen is five times or more, and the effect of increasing the amount of oxygen cannot be expected. Also,
If it is less than 0.5 times, the required amount of oxygen is insufficient, and the purification of wastewater is incomplete. In the range of 0.5 to 1 times, the COD component of the wastewater is completely converted to water, carbon dioxide, inorganic salts,
In addition, it is not enough as the amount of oxygen necessary to make ash. The reason for this is that the processing efficiency of COD is usually less than 100%, so that the supplied oxygen is not used 100% finally and remains, and in such a case, the supplied oxygen amount is increased by one time according to the actual processing efficiency. This is because the COD processing efficiency does not change so much even if it is reduced to less than.

As the wet oxidation treatment apparatus in the present invention, a commonly used wet oxidation apparatus is used. The wet oxidation reaction tower may be of a single-tube type or a multi-tube type, and the components contained in the wastewater may be used. Depending on the amount, single-tube type and multi-tube type can be treated alone or in combination. Further, the wet oxidation reaction tower may be any type of an adiabatic type or a heat-removal type, but the adiabatic type wet oxidation reaction tower is effective. A wastewater treatment system employing a heat removal type wet oxidation reaction tower often has a high COD concentration in the wastewater. For this reason, the heat removal type wet oxidation reaction tower takes away the generated heat with cooling water or steam, a hot water recovery system, etc. (hereinafter also referred to as a heat removal system), and forcibly prevents the wet oxidation reaction temperature from rising. Cooling. Therefore, when the heat removal system forcibly cooling the reactor is stopped, the reaction temperature can be kept relatively high, and the effect of the method according to the present invention may be reduced.

In the wet oxidation reaction apparatus of the present invention, the wet oxidation reaction tower can be filled with a filler made of metal or ceramic to improve the stirring of the liquid and gas, and the catalyst can be filled and treated. Efficiency can also be improved.

The catalyst described here may be any catalyst as long as it is a solid catalyst and has both activity and durability under the conditions of liquid phase oxidation. And a catalyst containing aluminum, zirconium, activated carbon, or the like. Preferably, an oxide such as titanium, titanium-zirconium, or titanium-iron is used. These catalysts may contain a second component in addition to the above components (hereinafter, referred to as a first component).

As the second component, at least one kind of metal such as manganese, cobalt, nickel, tungsten, copper, cerium, silver, platinum, palladium, rhodium, gold, iridium, ruthenium, or a component comprising these metal compounds Can be used. This catalyst is the first
The second component 25 to 25 to 99.95% by weight of the component
The proportion is preferably 0.05% by weight. In addition, various shapes can be adopted as the shape of the catalyst, and the shape is not particularly limited.

The treatment liquid discharged by the practice of the present invention can be directly discharged to rivers, seas, etc., and can be subjected to biological treatment or chemical treatment as post-treatment. Absent.

[0056]

According to the present invention, an easily decomposable substance is added in order to increase the treatment temperature and always treat harmful substances or COD components in wastewater with high treatment efficiency. More preferably, in order to prevent a decrease in the treatment temperature due to a low COD concentration of the wastewater during the wet oxidation treatment of the wastewater, or when the wet oxidation treatment apparatus is stopped, an insufficiently treated wastewater component is removed. This is implemented to prevent discharge.

In the former case, the treatment temperature is prevented from lowering due to a decrease in the calorific value obtained from the wet oxidation reaction due to a decrease in the concentration of COD or the like in the wastewater, and harmful substances or COD components in the wastewater are prevented. And the like can be purified with high processing efficiency even in such a case. Further, it is possible to avoid stopping the wet oxidation treatment reaction which occurs when the treatment temperature is further lowered. The present invention is a means for responding to such a case, and is intended to maintain the high purification performance of the wet oxidation treatment more stably by this method.

If the treatment temperature frequently decreases during wastewater treatment, it is more economical to install an external heating device according to the conventional method and supply heat from the outside than to the method according to the present invention. Sometimes it ’s good. However, in a normal processing apparatus, the processing temperature rarely decreases. For this reason, installing a conventional external heating facility for only a short period of time is very expensive in terms of facilities. However, the operation according to the method of the present invention is very simple and inexpensive in terms of equipment as compared with the conventional method, and the operability and the operation cost are easy, so that it is excellent in practicality and economy.

Further, in the wet oxidation treatment, a method is generally adopted in which the amount of air is adjusted and supplied in accordance with the amount of wastewater treated and the COD concentration. There is a possibility that adverse effects may occur, which is not preferable. In the present invention, since the COD concentration during normal operation is maintained, the amount of air is not reduced, so that it is possible to prevent a decrease in the activity of the wet oxidation treatment in such a case and to secure the stability of the treatment. You can do it.

The latter case is a method for stopping the wet oxidation treatment apparatus. It is intended to prevent the discharge of insufficiently treated wastewater when the wet oxidation treatment apparatus is stopped, or to reduce the discharge of insufficiently treated wastewater. It is intended to prevent the oxidant from remaining in the oxidation treatment system and to purify harmful substances or COD components in wastewater with high treatment efficiency even when the wet oxidation treatment device is stopped.

Generally, wet oxidation treatment equipment is designed such that heat generated by heat of oxidation or oxidative decomposition of harmful substances in wastewater is reused as heat for raising the temperature of the wastewater, and the wet oxidation treatment equipment becomes thermally independent. Have been. When stopping the conventional wet oxidation treatment apparatus, the supply liquid is switched from wastewater to water, the wet oxidation treatment apparatus system is replaced with water, and then the wet oxidation treatment apparatus is stopped, or the wastewater to the wet oxidation treatment apparatus is stopped. After the supply was stopped, the temperature of the wet oxidation treatment device was lowered while untreated wastewater remained in the wet oxidation treatment device. For this reason, CO that can be operated independently to stop the wet oxidation treatment
When the supply liquid to the wet oxidation treatment device is switched from the wastewater having a relatively high D concentration to the supply of water, the temperature of the wet oxidation treatment decreases, and the components of the wastewater remaining in the wet oxidation treatment device system are treated. It was discharged as a processing solution without being sufficient. Similarly, if the wet oxidizer is stopped and the temperature is lowered while the wastewater remains untreated in the wet oxidizer system, the components of this wastewater remain insufficiently treated during the next restart. It was discharged as a processing liquid. For this reason, when these incompletely treated wet oxidation treatment liquids are directly discharged, untreated substances such as harmful substances and COD components in the wastewater are directly discharged into rivers,
Hazardous substances and COD components in wastewater will flow into these treatment facilities untreated even if they are released to the sea and equipped with post-treatment facilities such as biological treatment or chemical treatment. In addition, there is a problem that the burden on the post-processing facility increases, and further, there is a problem that the post-processing facility cannot perform the processing.

That is, the treatment method of the present invention solves the above-mentioned problems, and prevents the incompletely treated wastewater from being discharged when the wet oxidation treatment apparatus is stopped, and is particularly limited to the following method. However, as an example, it is effective to carry out as follows. When the wet oxidation treatment is stopped, the supply of liquid to the wet oxidation treatment equipment is changed from wastewater to a liquid containing an easily decomposable substance, and while the wastewater remains in the wet oxidation treatment equipment, oxidation or oxidative decomposition of the easily decomposable substance The temperature of the wet oxidation treatment is maintained by the heat generated by the wastewater, and after the wastewater is sufficiently treated and only the easily decomposable substance is obtained, the supply of the easily decomposable substance is switched to the supply of only water, and the temperature of the apparatus is gradually lowered, and After the system is replaced with water, the apparatus is completely shut down. As a result, the wastewater supplied to the wet oxidation treatment device is
Since the wet oxidation treatment temperature is maintained due to the heat generated by the oxidation or oxidative decomposition of the easily decomposable substances, all the substances are discharged after being sufficiently treated. In addition, easily decomposable substances are easily treated with high treatment efficiency by wet oxidation even at relatively low temperatures, so wet oxidation is switched from supply of easily decomposable substances to supply of only water. Even if the treatment temperature of the oxidation treatment is lowered, the treatment of easily decomposable substances can be continued sufficiently to a relatively low temperature. Further, even if the easily decomposable substance remains and is discharged and is to be treated in a post-treatment facility, the easily decomposable substance is a substance which can be easily treated. It has good purifying properties.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

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Example 1 The catalytic wet oxidation apparatus shown in FIG. 1 was used. The reaction tower 1 has an inner diameter of 150 mm and a length of 10 m
And a catalyst comprising a composite oxide comprising titanium and zirconium and a catalyst comprising platinum (0.3% by weight) having a catalyst layer length of 9
m (volume of 159 liters).

The catalytic wet oxidation treatment of waste water was carried out using the above apparatus. After the treatment was stabilized, the supply of waste water was stopped, and the supply of water was simultaneously changed to the same amount. The easily decomposable substance was supplied using the easily decomposable substance supply pump 15, and the catalytic wet oxidation treatment was further continued for 4 hours. After 4 hours, the supply of the easily decomposable substance was stopped, and only the supply of water and air was performed.

The treatment liquid when the supply of the waste water is stopped,
From 45 minutes after stopping the supply of the wastewater to 75 minutes after the supply of the processing liquid and the easily decomposable substance, 7 minutes from 45 minutes after the supply was stopped.
The processing liquid up to 5 minutes later is stored in the processing liquid tank 14, and the TOC, COD (Cr) of each processing liquid, p-toluenesulfonic acid by liquid chromatography, and methanol by gas chromatography are measured to determine the concentration. Was.

The detailed usage of this treatment apparatus is as follows. The wastewater or water sent from the wastewater supply line 8 or the water supply line 17 is supplied to the wastewater supply pump 3 at 159 liter / water.
The pressure was increased to 80 kg / cm ² G at a flow rate of hr. On the other hand, after the air supplied from the oxygen-containing gas supply line 9 is pressurized by the compressor 5, O ₂ / COD (C
r) (Amount of oxygen in air / Chemical oxygen demand) = 1.2. This gas-liquid mixture is heated in a heat exchanger 2 through a gas-liquid mixture supply line 10 and then introduced into the reaction tower 1 from below, and subjected to a catalytic wet oxidation treatment.
The water to be treated was cooled in the heat exchanger 2 via the treated water line 11 and flowed to the gas-liquid separator 4. The space velocity of the waste water was 1.0hr¯ ^1. In the gas-liquid separator 4,
The liquid level controller (LC) detects the liquid level and activates the liquid level control valve 6 to maintain a constant liquid level. The pressure controller (PC) detects the pressure and activates the pressure control valve 7. It is operated to maintain a constant pressure. Then, the treated water is discharged from the treated water discharge line 13 and stored in the treated liquid tank 14. The easily decomposable substance is sent from the easily decomposable substance supply line 16 and is mixed with the gas-liquid mixture through the easily decomposable substance supply pump 15.

The TOC of the wastewater used for the treatment was 21.
It contained 6.2 g / l of p-toluenesulfonic acid at 4 g / l and 63.0 g / l of COD (Cr). In addition, methanol is used as the easily decomposable substance,
The mixture was supplied with a 20% by weight aqueous methanol solution so that the COD (Cr) concentration after mixing with water was 63.0 g / liter.

The results obtained were as follows. When the supply of wastewater was stopped, the outlet temperature of the reaction tower 1 was 261 ° C., the treatment liquid had a TOC concentration of 2.0 g / liter, and a COD (Cr) concentration of 5.
At 6 g / l, p-toluenesulfonic acid and methanol were not detected.

The outlet temperature of the reaction tower 1 was 258 ° C. 45 minutes after the supply of wastewater was stopped, and the outlet temperature was 257 minutes after 75 minutes.
At 45 ° C., the processing solution from 45 minutes to 75 minutes had a TOC concentration of 0.9 g / liter and a COD (Cr) concentration of 2.6 g / liter, and p-toluenesulfonic acid and methanol were not detected and were easily decomposed. The outlet temperature of the reactor 1 after 45 minutes from the supply of the substance was 249 ° C, and the outlet temperature after 75 minutes was 153 ° C.
At 45 ° C., the treatment liquid after 45 minutes to 75 minutes had a TOC concentration of less than 0.1 g / l and a COD (Cr) concentration of less than 0.1 g / l, and p-toluenesulfonic acid and methanol were not detected. .

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[0089] (Comparative Example 1) without the supply of the easily decomposable substance during the waste water supply stop in Example 1, was subjected to treatment while in Example 1 except that a direct waste water was fed only water.

As a result, the outlet temperature of the reaction tower 1 was 256 ° C. 45 minutes after the supply of wastewater was stopped, and the outlet temperature was 1 minute after 75 minutes.
At 57 ° C, the processing solution from 45 minutes to 75 minutes is TOC
Concentration 6.2 g / liter, COD (Cr) concentration 18.0 g /
In liters, p-toluenesulfonic acid was detected at 1.5 g / liter.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a catalytic wet oxidation treatment apparatus according to the present invention, particularly, a treatment apparatus shown in Example 1.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-7783 (JP, A) JP-A-4-300696 (JP, A) JP-A-55-92191 (JP, A) JP-A-58-1983 186496 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/74 B01J 19/00

Claims (2)

(57) [Claims] 1. An oxygen-containing gas is supplied at 150 ° C.
At a temperature of ３370 ° C. and under pressure where the wastewater retains the liquid phase,
The wastewater is supplied to a wet oxidation treatment apparatus , and the wet oxidation treatment operation is stopped in the wastewater treatment method for wet oxidation treatment.
The supply of wastewater to the wet oxidation treatment equipment
Switch to water containing volatile substances, and
A method for treating wastewater, wherein the wet oxidation treatment is stopped after switching to supply . 2. The method for treating wastewater according to claim 1, wherein the wet oxidation treatment device is a wet oxidation treatment device using a catalyst.