JP4455860B2 - Method and apparatus for treating oxidant - Google Patents

Description

The present invention relates to a method and apparatus for reducing an oxidizing agent contained in factory wastewater or groundwater with activated carbon , and more specifically, an oxidation capable of suppressing the deterioration of the activated carbon and maintaining the treatment effect of the oxidizing agent for a long period of time. The present invention relates to an agent processing method and apparatus.

  Oxidizing agents are widely used in various industries. For example, they have various uses such as decomposition of organic substances, regeneration of catalysts, reagents for forming compounds, and initiators for polymerization. In addition, an oxidant may be generated as a by-product in various processes such as heating, pressurization, and electrical treatment in industrial activities.

  Therefore, a large amount of oxidant is often present in wastewater generated by industrial activities, and there is a concern that if this wastewater is discharged as it is, the surrounding environment will be greatly affected. In addition, oxidizers in wastewater cause corrosion and deterioration of wastewater treatment facilities. Especially in biological treatment facilities such as activated sludge tanks, the presence of oxidizers in wastewater creates a useful group of microorganisms that act on the treatment. In order to give toxicity, it is necessary to treat the oxidizing agent in the waste water in advance. Furthermore, in recent years, as a method for purifying soil and groundwater contaminated with organic substances, a method has been studied in which an oxidizing agent is injected or added in situ to soil or groundwater to decompose the pollutants. In addition, it is often necessary to treat the remaining oxidizing agent.

  As a method for treating the oxidant-containing water as described above, conventionally, a method of adding a reducing agent such as sodium thiosulfate to the oxidant-containing water and discharging it after the reduction treatment has been used. Since the reaction of the agent takes time, a very large facility capable of securing the reaction time has been required. In addition, increasing the amount of reducing agent added at this time to shorten the reaction time means that the effect of promoting the reaction with respect to the increase in the amount added is weak, and in addition, surplus reduction remaining after the end of the reaction for consideration of the surrounding environment. It is not realistic because the agent needs to be processed. On the other hand, the oxidizing agent treatment method by contact with a catalyst (see, for example, Patent Documents 1 and 2) enables relatively quick treatment.

JP-A-8-168784 JP 2003-136092 A

  The oxidant treatment method by contact with the catalyst described above has a problem that the catalyst is easily deteriorated by the oxidant although the treatment is performed relatively quickly. For example, when activated carbon is used as the catalyst, if the oxidant concentration in the water to be treated is as high as 10 mg / L or more, the catalytic action of the activated carbon significantly decreases as the treatment proceeds. The running cost was high.

The present invention has been made in view of the above, it an oxidant treatment method and apparatus by contact with activated carbon to suppress the deterioration of the activated carbon, thereby long-lasting the treatment effect of the oxidizing agent with activated carbon It is an object of the present invention to provide a method and apparatus capable of performing the above.

In the treatment of oxidant-containing water with activated carbon, the present inventors have made hydrogen peroxide coexist in the water at the time of contact between the oxidant-containing water and activated carbon, so that deterioration of the activated carbon is greatly suppressed, and activated carbon It has been found that the treatment effect of the oxidant can be drastically sustained and the oxidant can be treated quickly and inexpensively.

The present invention has been made on the basis of the above-described knowledge. In the method for reducing the oxidizing agent of water containing an oxidizing agent having a higher oxidation- reduction potential than hydrogen peroxide as a reducing agent with activated carbon, Provided is a method for treating an oxidizing agent, wherein the water and the activated carbon are brought into contact with each other in a state where the oxidizing agent and hydrogen peroxide as a reducing agent coexist.

Further, the present invention includes activated carbon reactor to reduction treatment the oxidizing agent is contacted with water containing a redox potential than hydrogen peroxide as a reducing agent is high oxidizing agent and activated carbon, as a reducing agent to the water And a reducing agent addition means for adding hydrogen peroxide , wherein the water is passed through the activated carbon reaction tank in a state where the oxidizing agent and the hydrogen peroxide coexist in the water. An oxidizing agent processing apparatus is provided.

When the oxidizing agent in water and activated carbon are contacted, the oxidizing agent is reduced by the activated carbon, and the oxidizing agent can be efficiently processed. However, conventionally, the activated carbon deteriorates due to the reaction between the oxidizing agent and the activated carbon and gradually loses its activity. Therefore, it is necessary to periodically regenerate or replace the deteriorated activated carbon. In particular, when a high-concentration oxidizing agent is treated, the performance of activated carbon decreases very quickly, which increases the treatment cost. On the other hand, the present invention dramatically suppresses the deterioration of the activated carbon by allowing hydrogen peroxide to coexist as a reducing agent when the oxidizing agent and activated carbon are brought into contact with each other.

Hereinafter, the present invention will be described in more detail. In the present invention, the oxidizing agent to be treated is an oxidizing agent that can be reduced by activated carbon and has a higher redox potential than hydrogen peroxide as the reducing agent. The present invention includes, for example, permanganate, persulfate, and the like. It can be effectively applied to the treatment of salt and the like . Further, in the reduction treatment with activated carbon of water containing persulfate ions, the use of the present invention for the treatment of persulfate is very effective because the activated carbon deteriorates quickly and the cost of the activated carbon increases.

In the present invention, activated carbon is used as the catalyst. This is because activated carbon has a high reaction rate and is advantageous in terms of cost.

In the present invention, hydrogen peroxide is used as the reducing agent . For example, when the oxidizing agent is a persulfate , hydrogen peroxide , which is a substance having a lower redox potential than sulfuric acid radicals, can be suitably used as the reducing agent.

  INDUSTRIAL APPLICATION This invention can be effectively used for the process of the oxidizing agent used in order to add the oxidizing agent in soil, and to oxidize the contaminated organic substance which exists below the ground surface. For example, in a method of purifying by adding in situ oxidant to soil and groundwater contaminated with organic substances (in-situ chemical oxidation method), groundwater containing unreacted oxidant is recovered from the ground. It is effective when treating the oxidant in the recovered groundwater.

  In this case, examples of the oxidizing agent used in the in-situ chemical oxidation method generally include permanganate, persulfate (peroxodisulfate), hydrogen peroxide, and the like. Among these, permanganate is 10 to 100 times more toxic to aquatic organisms than persulfate as a result of tests using daphnia and medaka, and as manganese dioxide in the ground. Use with extreme caution as it remains. Although persulfate is less toxic than permanganate, it is a drug that has an oxidizing power and may be adversely affected by leakage into the environment. Since hydrogen peroxide may decompose in the ground and generate oxygen gas, when hydrogen peroxide is used, it is necessary to pay close attention to diffusion and flow in the ground. Considering the above points, it is particularly appropriate to use persulfate (or persulfuric acid) as an oxidizing agent in the in-situ chemical oxidation method. Examples of the persulfate include potassium persulfate and sodium persulfate.

  In the in-situ chemical oxidation method, the concentration of oxidant required for purification varies depending on the type of pollutant and soil properties. However, when persulfate is used as the oxidant, it is generally the end of the reaction region (purification It is desirable that it is 10-100,000 mg / L, particularly 100-50000 mg / L at the end of the range.

  The injected oxidant is consumed by reaction with pollutants and reducing substances in the soil, self-decomposition of the oxidant itself, catalysis by metals in the soil, and the like, resulting in a decrease in oxidant concentration. In addition, the oxidant concentration is lowered by the diffusion of the oxidant on the groundwater flow. If the oxidant consumption rate is very high and the injected oxidant falls to a safe concentration level in the controllable area, a safe cleanup is possible even with a system that only injects the oxidant. However, for example, when there is an aquifer in which groundwater exists, the oxidant consumption in the aquifer may not be sufficiently large. Furthermore, as the amount of oxidant injected increases, the soil reducibility is lost.

  In a purification system mainly consisting of oxidant injection, it is difficult to control the point and concentration of the oxidant, so the area to be purified should be hydraulically blocked by combining oxidant injection and pumping. Therefore, the system that prevents the oxidant from flowing out of the controllable area is very effective. In addition, by combining the injection of oxidant and pumping water, it becomes possible to control the flow rate of groundwater, so that the oxidant can quickly reach the target purification target area, resulting in shortening the purification period. I can expect. At this time, the amount of injection (return amount) is usually small compared to the amount of groundwater pumped, and if the surplus groundwater pumped contains residual oxidant that is not consumed in the ground, this oxidizer Need to be processed to a safe level. The groundwater containing the unreacted oxidant can be recovered from the ground by groundwater recovery means using a chemical recovery well, a water collection pipe, etc. installed in the ground, and can be treated according to the present invention.

As described above, according to the present invention, in the method and apparatus for reducing the oxidant of water containing an oxidant with activated carbon , deterioration of the activated carbon is suppressed and the treatment effect of the oxidant with activated carbon is maintained for a long period of time. be able to.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of an oxidizer treatment apparatus used in the practice of the present invention. In FIG. 1, 10 is an oxidizing agent-containing water introduction line, 12 is a reducing agent tank, 14 is a reducing agent addition line, 16 is a reducing agent addition pump, 18 is an activated carbon reaction tank, 20 is a treated water line, and 22 is pH adjustment and circulation. Treated water tank for water storage, 24 is a stirrer, 26 is an alkali agent tank, 28 is an alkali agent addition line, 30 is an alkali agent addition pump, 32 is a pH controller, 34 is a pH sensor, 36 is a treated water discharge line, and 38 is A treated water circulation line 40 is a circulation pump. In this apparatus, a reducing agent adding means is constituted by the reducing agent tank 12, the reducing agent addition line 14, and the reducing agent addition pump 16.

In this equipment, oxidant-containing water (for example, wastewater containing oxidant produced in the oxidant production process or groundwater containing unreacted oxidant recovered from the ground by the in-situ chemical oxidation method described above) Hydrogen peroxide is added from the reducing agent addition line 14 in the oxidizing agent-containing water introduction line 10. Thereafter, the oxidant-containing water is passed through the activated carbon reaction tank 18, and the treated water is stored in the treated water tank 22 through the treated water line 20. In the treated water tank 22, while the treated water 42 is stirred by the stirrer 24, an alkaline agent is added to the treated water 42 from the alkaline agent addition line 28, and the pH of the treated water is adjusted to near neutrality. A portion of the treated water whose pH is adjusted to near neutral is discharged from the treated water discharge line 36 to the outside of the system. Further, the remainder of the treated water flows into the treated water circulation line 38, where it is mixed with the water to be treated (oxidant-containing water), and then this mixed water is passed through the activated carbon reaction tank 18.

In this apparatus, by adding hydrogen peroxide to the oxidizing agent-containing water from the reducing agent addition line 14, the oxidizing agent-containing water and activated carbon are brought into contact in the activated carbon reaction tank 18 in a state where hydrogen peroxide is present. In this case, as the activated carbon filled in the activated carbon reaction tank 18, any type of coal, coconut shell, charcoal and the like can be used. In addition, as a means for contacting the oxidant-containing water and activated carbon, in addition to a fully mixed reactor such as a chemostat-type reaction tank or a batch-type reaction tank, a method of passing the liquid to be treated into a reaction tank filled with activated carbon, etc. However, since a large amount of activated carbon per unit area can be obtained, a fluidized bed type activated carbon packed tower which is an activated carbon packed reaction tank is desirable. As the shape of activated carbon, powder, granular, spherical, pellet, and fiber (with activated carbon supported on the fiber) can be used. In the case of using granular, pelletized or fibrous activated carbon, or a fully mixed reaction tank, it is desirable to use powdered or fibrous activated carbon having a high reaction rate.

Optimum pH of the water being treated with activated carbon reactor 18 varies depending oxidizing agent to be processed object, when processed oxidizing agent is persulfate acidic to neutral region is desirable. Treatment with an alkaline region accelerates the deterioration of the activated carbon. However, since the pH of water is usually lowered by sulfate ions generated by reduction treatment of persulfate ions, it is not always necessary to control the pH of water in the activated carbon reaction tank 18. Further, the oxidant decomposition at the time of contact with activated carbon is carried out relatively quickly by catalytic action, but the superficial velocity is desirably 50 or less, particularly 20 or less from the viewpoint of the quality of treated water.

As the reducing agent to be added from the reducing agent addition line 14, one that can react with the oxidizing agent to be treated, that is, one having a lower oxidation-reduction potential than the oxidizing agent to be treated can be used. For example, when persulfate is treated as an oxidizing agent, a sulfate radical is generated by contact with activated carbon. Therefore, a substance having a lower redox potential than this sulfate radical, specifically a substance having a redox potential of 2.6 eV or less is used. It can be used as a reducing agent. In the present invention, with such a reducing agent, hydrogen peroxide is used. In addition, the safety of chemicals, price, handling, and consider the need for such in the subsequent stage of processing, it is particularly desirable to use hydrogen peroxide.

Hydrogen peroxide only needs to be present in water when the oxidizing agent and activated carbon come into contact with each other. Therefore, hydrogen peroxide can be added before or simultaneously with the water to be treated in contact with activated carbon. Further, the hydrogen peroxide concentration at this time is calculated by the reaction formula of the oxidant and hydrogen peroxide, and is 1/10 of the equivalent when the reaction is completely performed with respect to the oxidant concentration measured in advance. The amount is about 10 to 10 times, preferably about 1/2 to 2 times the equivalent.

When processing water being treated by passing water contact with activated carbon reactor 18, the include persulfate ions as an oxidizing agent, because the gas is generated by the decomposition, the activated carbon reactor water flow in upflow By doing so, it is possible to prevent the accumulation of the gas in the apparatus, which is effective. In addition, by providing a treated water circulation line 38 that circulates the treated water together with the raw water to the activated carbon reaction tank, the linear flow rate in the activated carbon reaction tank is maintained high, and bubbles are prevented from adhering to the activated carbon. It produces desirable results such as reducing the apparent oxidant concentration. When such an up-flow type activated carbon reaction tank is adopted, activated carbon may flow out due to the generated bubbles, so a catalyst outflow prevention net, etc. is installed inside or at the outlet of the activated carbon reaction tank if necessary. There may be a need.

The material of the activated carbon reaction tank is preferably selected according to the quality of the water to be treated. In particular, when persulfate is included as the oxidizing agent in the water to be treated, it is appropriate to use an acid resistant material such as stainless steel or FRP because the pH is lowered by the decomposition of persulfate ions.

When the pH of water is lowered by the treatment with the oxidizing agent, it is necessary to neutralize the pH and discharge the treated water by adding an alkaline agent to the water before and / or after the activated carbon treatment. There are many cases. When neutralizing the pH after the activated carbon treatment, the treatment in the treated water tank 22 is performed from the alkaline agent addition line 28 while the treated water is being stirred by the stirrer 24 in the treated water tank 22 as in this example. An alkaline agent can be added to the water 42. In this case, the pH controller 32 can control the inflow of the alkaline agent. Alternatively, the pH sensor 34 may be installed in the treated water discharge line 36, and the alkaline agent may be added directly from the alkaline agent addition line 28 to the treated water in the treated water discharge line 36. In the above case, general alkaline substances such as sodium hydroxide, potassium hydroxide, sodium hydrogen carbonate, potassium carbonate, sodium carbonate can be used as the alkaline agent.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
As the oxidizing agent-containing raw water, a solution prepared by dissolving sodium persulfate in pure water to 500 mg / L was prepared in a vial. A system in which 100 mg / L of hydrogen peroxide or 80 mg / L of sodium thiosulfate is added to the raw water (reducing agent equivalent addition · An activated carbon non-water-permeable system) was created. In addition, a system added to the raw water so that the hydrogen peroxide is 400 mg / L or sodium thiosulfate 320 mg / L as about 4 times the equivalent (addition of 4 times equivalent of reducing agent / non-water activated carbon system) is prepared. In the system, the contact time with the reducing agent until the sodium persulfate concentration in water reached 100 mg / L or less was measured.

  On the other hand, water is passed through an activated carbon packed column in which a column made of acrylic resin (inner diameter: 30 mm, height: 300 mm) is packed with coal-based activated carbon (trade name: Diahop: manufactured by Mitsubishi Chemical Corporation) as a catalyst to a height of 100 mm. A system was created. The oxidant-containing raw water was passed through the column at a superficial velocity of 10 / hr, a part of the treated water was returned to the column inlet, and a circulation operation was performed at a linear flow rate of 17 m / hr (no reducing agent added, Activated carbon water flow system). In addition, in the raw water inflow line, hydrogen peroxide is continuously added to the raw water to be treated as a reducing agent at 100 mg / L (reducing agent addition / activated carbon flow system), and persulfate in the treated water in each system. The contact time until the sodium concentration reached 100 mg / L or less was measured.

  As a result, the contact time required to reduce the sodium persulfate concentration from 500 mg / L to 100 mg / L or less is 30 hours for the reducing agent (sodium thiosulfate) equivalent addition / active carbon non-water-passage system, and the reducing agent (sodium thiosulfate). ) Addition of 4 equivalents-Activated carbon non-water-permeable system 21 hours, Reducing agent (hydrogen peroxide) equivalent added-Activated carbon non-water-permeable system 140 hours, Reducing agent (hydrogen peroxide) 4 equivalents added-Activated carbon non-water-permeable system 136 The time was 0.1 hours in the case where no reducing agent was added and the activated carbon water was passed, and 0.1 hours in the case where the reducing agent was added and the activated carbon water was passed. Therefore, according to this experiment, in a system in which water was passed through an activated carbon packed column, sodium persulfate was rapidly changed from 500 mg / L to 100 mg / L by contact within the residence time at a superficial velocity of 10 / hr, regardless of whether a reducing agent was added. Although it was possible to process to less than L, in the case of reducing agent addition / active carbon non-water passage system, even if the amount of reducing agent added is four times that of reducing agent addition / active carbon water passage system, the contact time is 200 to 1400 times that It was confirmed that the treatment of the oxidant with activated carbon is very efficient.

(Example 2)
An acrylic resin column (inner diameter 30 mm, height 300 mm) was packed with coal-based activated carbon (Dia Hope; manufactured by Mitsubishi Chemical Corporation) as a catalyst so as to have a packing height of 100 mm. Then, water containing an oxidant was passed through this column, and the oxidant treatment ability when a single treatment with activated carbon was performed and when a reducing agent was allowed to coexist was examined. As the oxidizing agent-containing raw water, a solution prepared by dissolving sodium persulfate in pure water so as to be 500 mg / L was prepared. This raw water was passed through the column at a superficial velocity of 10 / hr, and in order to ensure a linear flow rate, a part of the treated water was returned to the column inlet and circulated at a linear flow rate of 17 m / hr. Here, in the raw water inflow line, hydrogen peroxide as a reducing agent was continuously added to the raw water to be treated at 100 mg / L or sodium thiosulfate at 83 mg / L. In addition, since a drop in the pH of the treated water was assumed, a pH controller was installed in the treated water tank installed at the column outlet, and sodium hydroxide was automatically added to the treated water in the treated water tank so that the pH was kept neutral. An aqueous solution was added. Furthermore, in the hydrogen peroxide addition system, activated carbon flows out due to the generation of a large amount of gas, so a net was installed above the activated carbon.

  The sodium persulfate concentration was measured for the raw water and treated water of the above apparatus, and the amount of water that can be maintained at 100 mg / L or less or 200 mg / L or less in the treated water was determined. On the other hand, the system which does not add a reducing agent was created, and the processing result was compared. As a result, the amount of water that can be maintained at a sodium persulfate concentration of 100 mg / L or less in the treated water is 150 L for the reducing agent-free system, 1100 L for the hydrogen peroxide-added system, and 600 L for the sodium thiosulfate system. The amount of water that can be maintained at a sodium sulfate concentration of 200 mg / L or less was 220 L in the system without addition of a reducing agent, 2800 L in the system with hydrogen peroxide, and 1300 L in the sodium thiosulfate system. Therefore, according to this experiment, both the hydrogen peroxide-added system and the sodium thiosulfate-added system increase the water flow rate by more than 4 to 10 times compared to the system without the reducing agent, and the addition of the reducing agent is very effective. Was confirmed. In all the systems, the pH at the column outlet dropped to about 2, but the final treated water pH was kept neutral by the action of the neutralizer.

It is a figure which shows an example of the oxidizing agent processing apparatus used for implementation of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Oxidizer containing water introduction line 12 Reductant tank 14 Reductant addition line 16 Reductant addition pump 18 Activated carbon reaction tank 20 Treated water line 22 Treated water tank 24 for pH adjustment and circulation water storage 24 Stirrer 26 Alkali agent tank 28 Alkaline agent addition Line 30 Alkali agent addition pump 32 pH controller 34 pH sensor 36 Treated water discharge line 38 Treated water circulation line 40 Circulation pump

Claims (6)

In the method of reducing the oxidizing agent of water containing an oxidizing agent having a higher oxidation-reduction potential than hydrogen peroxide as a reducing agent with activated carbon, the oxidizing agent and hydrogen peroxide as a reducing agent coexist in the water. In this state, the water and the activated carbon are brought into contact with each other.   The method for treating an oxidizing agent according to claim 1, wherein the oxidizing agent is a persulfate. An activated carbon reaction tank for reducing the oxidizing agent by contacting activated carbon with water containing an oxidizing agent having a higher oxidation-reduction potential than hydrogen peroxide as a reducing agent , and adding hydrogen peroxide as a reducing agent to the water An oxidant processing apparatus comprising: a reducing agent adding means, wherein the water is passed through the activated carbon reaction tank in a state where the oxidant and the hydrogen peroxide coexist in the water.   The oxidant treatment apparatus according to claim 3, wherein the oxidant is a persulfate. The oxidant treatment apparatus according to claim 3 or 4, wherein the water is passed through the activated carbon reaction tank in an upward flow. The processing apparatus of the oxidizing agent of any one of Claims 3-5 which provided the treated water circulation line which circulates the treated water of the said activated carbon reaction tank to the said activated carbon reaction tank with the said water.