JP7166795B2 - Method for treating wastewater containing COD components - Google Patents

Description

The present invention relates to a method for treating wastewater containing COD components indicated by a COD value (chemical oxygen demand), and more specifically, adsorption by activated carbon, which has been required in the prior art to reduce the COD value in treated water. A method for treating wastewater containing COD components that can achieve a reduction in the COD value of the final treated water in spite of the fact that the amount of activated carbon used in the treatment can be greatly reduced by a simple method that can eliminate processes. Regarding.

For example, in the steel manufacturing industry, a large amount of wastewater containing oil and persistent organic matter is generated from rolling processes using rolling oil, and it is necessary to purify the wastewater. When treating wastewater containing COD components that contain contaminants such as persistent organic matter, the conventional method generally used is to first coagulate the water to be treated with SS (suspended Substances) treatment, followed by oxidative decomposition of persistent organic matter in the oxidative decomposition step, and then activated carbon adsorption (using an activated carbon adsorption tower) in the final step. As a method for increasing the decomposition efficiency of persistent organic matter, for example, a method of chemical oxidation treatment using an oxygen-based oxidant such as hydrogen peroxide and a metal catalyst that produces iron ions, etc. (for example, patent Accelerated oxidation, such as a method using ozone having a strong oxidizing power (see, for example, Patent Document 2), is widely used as a useful method.

In the conventional treatment method as described above, it is common to further perform activated carbon adsorption after the oxidative decomposition treatment. The reason for this is that the COD value in the treated water cannot be lowered to the target value only by the flocculation treatment and the subsequent oxidative decomposition. In recent years, the importance of environmental protection has been recognized more than ever before, and emission regulations have become more stringent. Therefore, COD < 10 mg/L is required, and a very strict value is required, and the importance of final treatment by activated carbon adsorption is increasing.

In Patent Document 3, when coagulating and sedimenting suspended solids in COD wastewater containing oil, COD components, and nitrogen components, which has a different configuration from the widely used wastewater treatment containing COD components, coagulation sedimentation is performed. In the tank, 0.1% to 10% (relative to the wastewater) of powdered activated carbon is added to the wastewater for adsorption treatment, and then an inorganic powder flocculant composed of inorganic granules mainly composed of activated silicon dioxide and alumina is added. A method has been proposed in which 50 ppm to 10,000 ppm (relative to waste water) is added to simultaneously treat oil, COD components and nitrogen components. According to this technique, it is not necessary to subject the supernatant water after the flocculation treatment to a flocculation treatment using a polymer flocculant or a water permeation treatment using a membrane.

Japanese Patent No. 4662059 Japanese Patent Application Laid-Open No. 2001-321787 Japanese Patent No. 4169614

The inventors of the present invention have made intensive studies on improving the efficiency of treatment in a simple manner with the aim of enabling more economical treatment in view of the above-described technical state of the treatment of wastewater containing COD components. . Here, in the method of performing treatment in the order of coagulation treatment → accelerated oxidation treatment → adsorption treatment with activated carbon, which is widely used in the conventional treatment technology of wastewater containing COD components, the COD treatment rate with activated carbon is low. However, there is a problem that the amount of COD to be removed in the preceding oxidation treatment step increases (the load is high), and a more efficient oxidation treatment is required. In this respect, for example, hydrogen peroxide and iron are used to generate OH radicals with a strong oxidizing action (Fenton method), and ozone oxidation methods using ozone with a strong oxidizing power. An accelerated oxidation method has been proposed. However, in any method, final treatment by activated carbon adsorption is required in order to make the COD value in the treated water satisfy the strict discharge standards. In the course of the study, the inventors found that in the above-described method in which the processes are performed in the order of coagulation treatment → accelerated oxidation treatment → adsorption treatment with activated carbon, the adsorption efficiency with activated carbon is poor, so the amount of activated carbon used is large. We realized that if we could not improve this, it would be difficult to reduce running costs and establish a more efficient and economical treatment method.

In addition, in Patent Document 3 mentioned above, powdered activated carbon is added to the waste water in the coagulation sedimentation tank, and after adsorption treatment, it is treated with a unique inorganic coagulant, so that oil, COD components, and nitrogen components The powdered activated carbon that has been adsorbed coagulates and sediments with a unique inorganic coagulant to form coagulated sedimentation sludge, which can be treated all at once. Since it is a technology, it naturally requires a large amount of activated carbon. Since activated carbon is relatively expensive, even if it is possible to eliminate the need to treat the supernatant water with a polymer flocculant, this is an important problem in the practical use of wastewater treatment. It is not possible to achieve cost reduction. Furthermore, a large amount of activated carbon contained in the coagulated sedimentation sludge after coagulation and sedimentation with a unique inorganic coagulant adsorbs oil, COD components, and nitrogen components, so it cannot be reused. .

Therefore, the object of the present invention is to sequentially perform the processes of coagulation treatment → accelerated oxidation treatment → adsorption treatment with activated carbon, which is widely used as a purification treatment technology for industrial wastewater containing a large amount of COD components in the steel manufacturing industry. Regarding the improvement of the general treatment method of wastewater containing /L, and even COD < 10 mg/L, and furthermore, it is possible to eliminate the need for the final adsorption treatment with activated carbon. Another object of the present invention is to realize a method for treating waste water containing COD components, which is excellent in terms of

The above objects are achieved by the present invention described below. That is, the present invention provides the following method for treating wastewater containing COD components.
[1] A method for treating wastewater containing COD components that can eliminate the need for an adsorption step with activated carbon after an oxidation treatment step, wherein in the coagulation treatment step with a coagulant performed prior to the oxidation treatment step, an inorganic coagulant is added to the water to be treated After adding and treating, the water to be treated is further treated by adding an organic flocculant, and when adding the inorganic flocculant, activated carbon is added to allow the inorganic flocculant and activated carbon to coexist. A method of treating wastewater containing COD components, characterized by:

Preferred embodiments of the method for treating wastewater containing COD components according to the present invention include the following inventions.
[2] The inorganic flocculant is an aluminum flocculant containing aluminum sulfate, polyaluminum chloride and aluminum chloride, and/or an iron flocculant containing ferric sulfate, ferric chloride and polyferric sulfate. being at least one selected from the group;
[3] The activated carbon is a powder having an average particle size of 200 μm or less and a specific surface area of 800 to 2000 m ² /g, and the powder is dispersed in water and added;
[4] The treatment in the oxidation treatment step is an oxidation promotion treatment using hydroxyl radicals generated by an oxygen-based oxidant and a metal catalyst, and the amount of the activated carbon added to the amount of the oxygen-based oxidant used is the ratio is between 0.5 and 20;
[5] The treatment in the oxidation treatment step is oxidation promotion treatment using ozone;
[6] After the treatment in the oxidation treatment step, adding an organic flocculant to the water to be treated for flocculation;
[7] The amount of the activated carbon to be added is 1 to 10 times the COD component.

According to the present invention, the final adsorption treatment with activated carbon can be made unnecessary, the amount of activated carbon used can be greatly reduced, and COD can be removed more efficiently in the oxidation step by accelerated oxidation. Thus, an economical and industrially useful method for treating wastewater containing COD components can be realized. In addition, according to a preferred embodiment of the present invention, it is possible to realize an industrially useful method for treating wastewater containing COD components that achieves both a more effective oxidation treatment and a reduction in the amount of flocculated sediment generated by the treatment. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a treatment flow for explaining an example of a method for treating wastewater containing COD components according to the present invention; 4 is a graph showing the relationship between the amount of sludge (SS) generated in the treatment methods of Examples 2 to 8 of the present invention and Comparative Examples 3 and 4, and the ratio of the amount of activated carbon added to the amount of oxidizing agent used. FIG. 3 is a graph showing the relationship between the amount of sludge (SS) generated and the ratio of the amount of activated carbon added to the amount of oxidizing agent used, in which the value on the horizontal axis of FIG. 2 is expressed in logarithm. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a treatment flow for explaining an example of a conventional method for treating wastewater containing COD components.

Preferred embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.
As shown in FIG. 1, the method for treating wastewater containing COD components according to the present invention has a basic flow similar to that of the prior art shown in FIG. The oxidation treatment is performed to decompose the COD components, and there is a remarkable effect that the final activated carbon adsorption step, which is essential in the conventional treatment flow shown in FIG. 4, can be eliminated.

As described above, the present inventors are keen to find a simple method that can increase the treatment efficiency for the purpose of enabling more economical treatment of wastewater containing COD components. Study was carried out. In the process, in the coagulation treatment step in which the treatment with the inorganic coagulant is performed prior to the oxidation treatment step, followed by the treatment with the organic coagulant, the wastewater containing the COD component, which is the water to be treated, is first subjected to inorganic coagulation. When the agent is added and treated, activated carbon is added and the inorganic flocculant and activated carbon are allowed to coexist for treatment. As a result, it is possible to realize an extremely useful effect from an industrial point of view, which eliminates the need for an adsorption step with an activator, which was provided as the final step in the conventional method, and is more economical. It was found that efficient treatment can be achieved by

As described in Patent Document 3 cited above as prior art, activated carbon adsorbs oil, COD components and nitrogen components in wastewater. In the technique described in Patent Document 3, first, activated carbon adsorbs oil, COD components, and nitrogen components in wastewater, and then the activated carbon adsorbed with the oil and COD components is aggregated with a specific inorganic flocculant. I am letting That is, the technique of Patent Document 3 is to fully exhibit the adsorption ability of activated carbon for oil, COD components, and nitrogen components, and then add a specific inorganic flocculant to remove oil such as sludge in wastewater. With this, the COD component and the nitrogen component can be treated at the same time, and the flocculation property of the activated carbon and the sedimentation property of the flocculated activated carbon are very good. On the other hand, the present inventors found that when the inorganic flocculant is first added and treated in the flocculation step, activated carbon is added to allow the inorganic flocculant and activated carbon to coexist. The present invention has been achieved by discovering that the efficiency of the subsequent oxidative decomposition treatment is remarkably improved.

The inventors of the present invention consider the reason why the above-described remarkable effects are obtained as follows. For example, waste water from rolling processes using rolling oil, which is produced in large amounts in the steel manufacturing industry, contains various contaminants such as oil and persistent organic matter (COD). These contaminants in the wastewater are considered to coexist with components such as organic matter having various molecular weights. In general, the adsorption performance to activated carbon depends on its molecular weight, and the larger the molecular weight of an organic substance, the easier it is to adsorb. Conversely, an organic substance with a small molecular weight is less adsorbable to activated carbon than an organic substance with a large molecular weight. From these facts, the present inventors speculate as follows about the reason why the above-described remarkable effects are obtained in the processing method of the present invention.

In the existing COD treatment method in which an adsorption step with activated carbon is provided after the oxidative decomposition step, the oxidation step decomposes organic substances with large molecular weights into components with small molecular weights, so the adsorption performance to activated carbon is lowered. Therefore, the amount of activated carbon required in the activated carbon adsorption step increases, and the amount of oxidizing agent used in the oxidation step increases in order to reduce the COD load in the activated carbon adsorption step. On the other hand, in the treatment method of the present invention, adsorption by activated carbon is performed before the adsorption performance of the COD components is lowered by oxidation in the oxidation step, so the adsorption efficiency by activated carbon is increased, and the amount of activated carbon can be reduced. can be done. In addition, the amount of oxidizing agent used in the oxidation step can be reduced as the amount of adsorption and removal by activated carbon is improved. The reason why the treatment method of the present invention does not require the activated carbon adsorption step after the oxidation step, which is essential in the existing COD treatment method, is considered to be realized by the combination of the above effects. That is, by adding activated carbon in the coagulation step preceding the oxidation step and performing activated carbon adsorption, persistent COD is efficiently adsorbed and removed, so that the oxidation efficiency by the oxidizing agent in the subsequent oxidation step is also improved. , it is considered that the above excellent effects could be realized.

Next, the objects to be treated, chemicals to be used, treatment conditions, etc., which constitute the method for treating wastewater containing COD components of the present invention, will be described. The method of the present invention is applied, for example, to a method of treating oil and COD in alkaline wastewater in the rolling process of the steel manufacturing industry in a good state, similar to the invention described in Patent Document 1 presented as prior art. This allows for more effective processing. That is, the treatment method of the present invention, like the invention described in Patent Document 1, achieves COD < 20 to 30 mg / L, and further COD < 10 mg / L, which is required for treated water after purification treatment. Compared to the invention described in Patent Document 1, in particular, the final treatment by activated carbon adsorption can be eliminated, so the amount of activated carbon used for purification treatment can be significantly reduced. Since the efficiency of the oxidative decomposition treatment can be improved, the effect of reducing the amount of chemicals used for oxidative decomposition can be obtained, and more economical and efficient treatment can be achieved.

[Water to be treated]
The treatment method of the present invention can be applied to any of various wastewaters containing COD components. For example, a greater effect can be obtained when applied to purification treatment of wastewater with a total COD of 20 to 1500 mg/L and a soluble COD of 20 to 1000 mg/L. Examples of the water to be treated exhibiting such properties include various types of wastewater, such as those listed below. Specifically, for example, landfill wastewater, natural gas processing wastewater, night soil biologically treated water, livestock manure-containing water, slaughterhouse wastewater, pulp manufacturing wastewater, beverage manufacturing wastewater such as coffee and tea, sugar manufacturing wastewater, soy sauce and miso manufacturing Brewery wastewater, waste molasses (glutamic acid production, yeast production, production of other fermented microbial products, etc.) wastewater, petroleum refining wastewater, coal chemical wastewater, coke oven gas condensate (ammonia water), petrochemical wastewater, pyrolysis process wastewater, Salting-out waste, distillation still residue, electroless plating waste, water-soluble polishing/rolling oil waste, metal surface treatment degreasing waste (from precision machining to steel and automobile manufacturing), photo development waste, photoresist waste, oleochemistry/ Surfactant production wastewater and the like can be mentioned.

[Aggregation treatment step]
In the treatment method of the present invention, in the flocculation treatment step using a flocculant performed prior to the oxidation treatment step, first, an inorganic flocculant is added to the wastewater for treatment, and then an organic flocculant is added to the wastewater for treatment. . The method is characterized in that activated carbon is added when adding the inorganic flocculant, and the inorganic flocculant and activated carbon coexist in the treatment. First, the chemicals used in the aggregation treatment process will be described.

<Inorganic flocculant>
As the inorganic flocculant used in the present invention, any conventionally known one used for treating suspended solids (SS) in wastewater can be used. Specifically, an aluminum-based coagulant, an iron-based coagulant, or the like can be used. Examples of aluminum-based flocculants include aluminum sulfate, polyaluminum chloride, and aluminum chloride. Examples of iron-based coagulants include ferric sulfate, ferric chloride and polyferric sulfate. One or more of these can be appropriately selected and used. The amount to be added may be appropriately determined according to the concentration of contaminants in the wastewater, and may be added in the range of 50 to 1000 mg/L, for example.

<Activated carbon>
In the processing method of the present invention, activated carbon is added when adding the above-described inorganic flocculant, and the coexistence of the inorganic flocculant and activated carbon is carried out. Here, the provision that "activated carbon is added when adding the inorganic flocculant" means that even if the inorganic flocculant is added and the activated carbon is added at the same time, the activated carbon is added before the inorganic flocculant is added. It means that it may be added and treated, or the activated carbon may be added after the addition of the inorganic flocculant. means good. In particular, it is preferable to add the activated carbon simultaneously with the addition of the inorganic flocculant, or to add the activated carbon before adding the inorganic flocculant. As the activated carbon to be used, any activated carbon that has been conventionally used for treating waste water and wastewater can be used. For example, it is preferable to use powdered activated carbon having an average particle size of 200 μm or less, which is obtained using wood, coal, and coconut shells as raw materials. More preferably, a powder having an average particle size of about 1 to 150 μm, more preferably about 1 to 100 μm is used. For example, any commercially available product with 150 μm pass≧90% and 75 μm pass≧90% can be used. It is preferred to use powdered activated carbon with a specific surface area of 800-2000 m ² /g.

Also, if the amount of activated carbon added when adding the inorganic flocculant is about 1 to 10 times the COD component, a good effect can be stably obtained. In addition, according to the studies of the present inventors, when the method used in the subsequent oxidation treatment step is oxidation promotion treatment using hydroxyl radicals generated by an oxygen-based oxidant and a metal catalyst, It is preferable that the ratio of the amount of the oxygen-based oxidant used is 0.5 to 20, more preferably 1.0 to 12. As will be described later, by configuring in this way, it is possible to reduce the amount of sludge (SS) generated after treatment, and to reduce the problem of subsequent secondary treatment of the sludge.

<Organic flocculant>
As the organic flocculant used in the present invention, any conventionally known polymer flocculant used for treating suspended solids (SS) in wastewater can be used. It may be anionic, cationic, or amphoteric. Examples of anionic polymer flocculants include polyacrylamide-based agents, anionic polyacrylamide-based agents, and partial hydrolysates of polyacrylamide. Examples of cationic polymer flocculants include polyvinylamidine containing acrylate, methacrylate, amide group, nitrile group, amine hydrochloride, formaldehyde group, and the like. Amphoteric polymer flocculants include, for example, a copolymer of dimethylaminomethyl acrylate quaternary, acrylamide and acrylic acid, and a copolymer of dimethylaminomethyl methacrylate quaternary, acrylamide and acrylic acid. mentioned.

The amount of the polymer flocculant used as mentioned above may be appropriately determined according to the concentration of pollutants in the wastewater, but it is in the range of 1 to 5 mg per liter of raw water (water to be treated). , in the range of 1 to 2 mg per liter. In the treatment method of the present invention, the treatment in the oxidation treatment step described later, which is performed after the treatment with the organic flocculant in the flocculation treatment step, is performed as an oxidation promotion treatment using hydroxyl radicals generated by the oxygen-based oxidant and the metal catalyst. In the case of , suspended solids are generated, so it becomes necessary to perform a flocculation treatment using a polymer flocculant such as those listed above for the water to be treated after the oxidation treatment. In that case, the amount of the polymer flocculant used may be in the range of 1 to 5 mg per liter of water to be treated, and further in the range of 1 to 2 mg per liter.

[Procedure for aggregation treatment]
In the method of treating wastewater containing COD components according to the present invention, the treatment is performed as shown in the schematic flow diagram of FIG. As shown in FIG. 1, first, an inorganic coagulant and activated carbon powder are added to raw water, which is water to be treated, and coagulation treatment is performed while stirring. As a result, agglomerates containing activated carbon, to which a part of the contaminants are adsorbed, and the inorganic flocculant settle. Next, an organic flocculant, which is a polymer flocculant, is added to the water to be treated for flocculation treatment. As a result, contaminants in the water to be treated are aggregated and sedimented to be removed as sediments. Then, the supernatant water obtained by the solid-liquid separation becomes the water to be treated in the next oxidative decomposition step.

[Oxidation treatment step]
The treatment method of the present invention is characterized in that the flocculation treatment using the above-described flocculating agent using activated carbon is performed prior to the oxidation treatment step. The treatment in the subsequent oxidation treatment step may be a conventionally known method, for example, chemical oxidation promotion treatment using hydroxy (OH) radicals generated by an oxygen-based oxidant and a metal catalyst, or ozone oxidation using ozone. Any conventionally known method such as accelerated treatment can be used. Chemical oxidation promotion treatment will be described below as a typical example. Any type of oxygen-based oxidizing agent may be used in the chemical oxidation promotion treatment as long as it reacts with a metal catalyst to generate OH radicals. Specifically, hydrogen peroxide, ozone and the like can be mentioned, and hydrogen peroxide is preferably used. The amount used depends on the amount of organic matter in the water to be treated and the type of oxygen-based oxidizing agent, but is preferably about 100 to 550 mg per liter of water to be treated, for example. As the metal catalyst, those that generate at least one of iron ions, nickel ions, cobalt ions and copper ions in the water to be treated are preferably used. These react with an oxygen-based oxidant such as hydrogen peroxide to generate OH radicals. Specific examples include ferrous chloride, ferrous sulfate, nickel chloride and cobalt chloride. Among these, iron-based catalysts are preferred. The amount of the oxygen-based oxidizing agent to be used depends on the type and amount of the oxygen-based oxidizing agent.

The reaction between the oxygen-based oxidizing agent and the metal catalyst during the chemical oxidation treatment is preferably carried out in an acidic range of pH 2-4. In this case, if the reaction pH is less than 2, the amount of alkaline agent used for neutralization in the pH adjustment step after the completion of the reaction increases, which is not economical. On the other hand, if the reaction pH is more than 4, the metal catalyst will precipitate as a hydroxide and will not be effectively used as a metal catalyst, so that the oxidation reaction will not proceed efficiently. Further, in the above reaction, the reaction molar ratio between the oxygen-based oxidizing agent and the metal catalyst is preferably in the range of 2-7. By performing the chemical oxidation treatment under such conditions, the COD components in the water to be treated can be efficiently decomposed and removed.

When the oxidation in the oxidation treatment step is carried out by the chemical oxidation treatment described above, the treated water obtained is acidic, and therefore needs to be neutralized with an alkali when discharged. In addition, since a metal catalyst is used in the above chemical oxidation treatment, suspended solids caused by the metal catalyst remain in the water to be treated after neutralization. Therefore, in this case, it is necessary to perform a flocculation treatment with an organic flocculant to remove suspended solids caused by the metal catalyst. In the treatment method of the present invention, the efficiency of the oxidation treatment process is improved, and the amount of the oxygen-based oxidizing agent and metal catalyst used in the oxidation treatment can be reduced. There is an advantage that the amount of (sludge) can be reduced. Therefore, the load on the secondary treatment of the sludge is reduced, and in this respect as well, a superior effect can be obtained as compared with the conventional method.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited by the following examples.

[Example 1]
200 mL of waste water was collected in a beaker. This wastewater is from the rolling process of a steel mill and has a soluble COD concentration of 37 mg/L. Using this wastewater as raw water to be treated, the following treatment was performed in the flocculation treatment step using a flocculant performed prior to the oxidation treatment step. 50 mg/L of activated carbon powder (average particle size: 13 μm) and 148 mg/L of polyaluminum chloride (PAC) were added to the collected wastewater, and stirred for 15 minutes while adjusting the pH to 7 with sulfuric acid. did. In the above, the activated carbon powder and PAC were added almost simultaneously. Subsequently, a polyacrylamide polymer flocculant KEA-735 (trade name, manufactured by Nippon Steel & Sumikin Kankyo Co., Ltd.) was added to the water to be treated so as to have a concentration of 2 mg/L, and the mixture was stirred for 1 minute to remove contaminants in the wastewater. was flocculated with the activated carbon and flocculant used in the treatment. Next, the generated aggregates/precipitates were removed in a solid-liquid separation step to obtain supernatant water.

Using the supernatant water obtained above as the water to be treated, in the next oxidation treatment step, hydrogen peroxide is added to the water to be treated so that 126 mg / L and ferric chloride is 750 mg / L, and the pH is 3 with sulfuric acid. Accelerated oxidation treatment was performed by stirring for 7.5 minutes while adjusting to . After the treatment, the pH of the liquid to be treated was adjusted to pH 7 with caustic soda, and stirred for 7.5 minutes in that state. Next, the same polymer flocculant as used in the previous flocculation treatment step was added in an amount of 2 mg/L and stirred for 1 minute to flocculate the suspended solids. Finally, the produced aggregate was removed by solid-liquid separation to obtain supernatant water. The finally obtained soluble COD concentration in this supernatant water was 10 mg/L. A summary of the treatments and results is summarized in Table 1. In the above, when the activated carbon powder was added and then the PAC was added and tested, the same effect as the above was obtained.

[Comparative Example 1]
200 mL of waste water similar to that used in Example 1 was collected in a beaker. 148 mg/L of polyaluminum chloride was added thereinto and stirred for 15 minutes while adjusting the pH to 7 with sulfuric acid. Next, the same polymer flocculant as used in Examples was added to 2 mg/L and stirred for 1 minute to flocculate the suspended solids. Next, the generated aggregates/precipitates were removed in a solid-liquid separation step to obtain supernatant water.

Using the supernatant water obtained above as the water to be treated, in the next oxidation treatment step, hydrogen peroxide is added to the water to be treated so that 256 mg / L and ferric chloride is 1500 mg / L, and the pH is 3 with sulfuric acid. It was stirred for 7.5 minutes while adjusting to . After treatment, the pH was adjusted to 7 with caustic soda and stirred for 7.5 minutes. Finally, the same polymer flocculant as used in the previous flocculating step was added in an amount of 2 mg/L and stirred for 1 minute to flocculate the suspended solids. The produced aggregate was removed by solid-liquid separation to obtain supernatant water. In this comparative example, 300 mg/L of activated carbon was added to the supernatant water separated above and stirred for 7.5 minutes for adsorption treatment. The final supernatant water (treated water) had a soluble COD concentration of 10 mg/L. A summary of the treatments and results is summarized in Table 1.

[Comparative Example 2]
200 mL of waste water similar to that used in Example 1 was collected in a beaker. 900 mg/L of activated carbon powder (average particle size: 13 μm) was added thereinto and stirred for 7.5 minutes. Then, 148 mg/L of polyaluminum chloride was added, and the mixture was stirred for 7.5 minutes while adjusting the pH to 7 with sulfuric acid to flocculate suspended matter. Next, the generated aggregates/precipitates were removed in a solid-liquid separation step to obtain supernatant water.

[Examples 2 to 8, Comparative Examples 3 and 4]
In Examples 2 to 8, the amount of activated carbon used in the flocculation treatment step of Example 1 and the amount of chemicals used in the oxidation treatment were changed as shown in Table 2 for 200 mL of the same wastewater used in Example 1. Treatment was carried out in the same manner except for The amount of chemicals used for the oxidation treatment is indicated by the amount of hydrogen peroxide as an oxidizing agent. The amount of ferric chloride used as a metal catalyst was determined according to the amount of hydrogen peroxide used. In Comparative Example 3, the treatment was performed without adding activated carbon when adding the inorganic flocculant. In Comparative Example 4, a large amount of activated carbon was used to perform flocculation treatment, and the treatment was performed without oxidation treatment. During the treatment, the amount of the chemical added was adjusted so that the finally obtained treated water (supernatant water) had a soluble COD concentration of 11 mg/L. Table 2 shows the ratio of the amount of activated carbon used to the amount of oxidizing agent used and the amount of sludge (SS) generated in each treatment. 2 and 3 show the relationship between the amount of generated sludge (SS) and the ratio of the amount of activated carbon used to the amount of oxidizing agent used.

As shown in Table 2, Figures 2 and 3, in Comparative Example 3 in which no activated carbon was added, the amount of sludge generated was extremely large, whereas the ratio of the amount of activated carbon used to the amount of oxygen-based oxidant used However, it was confirmed that in Examples 3 to 6 where the ratio was 0.5 to 12, the amount of hydrogen peroxide as an oxidizing agent could be reduced, and a remarkable effect could be obtained that the amount of sludge generated could be reduced.

Claims (7)

A method for treating wastewater containing COD components that can eliminate the need for an adsorption step with activated carbon after an oxidation treatment step, wherein in the coagulation treatment step with a coagulant performed prior to the oxidation treatment step, an inorganic coagulant and activated carbon are added to the water to be treated. Supernatant water obtained by adding an inorganic flocculant and activated carbon to coexist for flocculation treatment, then adding an organic flocculant to the water to be treated for flocculation treatment, and performing solid-liquid separation after the flocculation treatment step. is the water to be treated in the oxidation treatment step, the treatment in the oxidation treatment step is an oxidation treatment using hydroxyl radicals generated by an oxygen-based oxidant and a metal catalyst , and the oxygen-based oxidant is used A method for treating wastewater containing COD components, wherein the ratio of the added amount of the activated carbon to the amount is 0.01-20. The inorganic flocculant is selected from the group consisting of aluminum-based flocculants containing aluminum sulfate, polyaluminum chloride and aluminum chloride, and/or iron-based flocculants containing ferric sulfate, ferric chloride and polyferric sulfate. The method for treating wastewater containing COD components according to claim 1, wherein at least one of The waste water containing COD components according to claim 1 or 2, wherein the activated carbon is a powder having an average particle size of 200 μm or less and a specific surface area of 800 to 2000 m ² /g, and the powder is dispersed in water and added. Processing method. The treatment in the oxidation treatment step is oxidation promotion treatment using hydroxyl radicals generated by an oxygen-based oxidant and a metal catalyst, and the ratio of the amount of activated carbon added to the amount of the oxygen-based oxidant used is The method for treating wastewater containing COD components according to any one of claims 1 to 3, wherein the COD component is 0.5 to 20. The method for treating wastewater containing COD components according to any one of claims 1 to 3, wherein the oxygen-based oxidant is hydrogen peroxide. The method for treating wastewater containing COD components according to any one of claims 1 to 5, wherein after the treatment in the oxidation treatment step, an organic coagulant is added to the water to be treated for coagulation treatment. The method for treating wastewater containing COD components according to any one of claims 1 to 6, wherein the amount of activated carbon to be added is 1 to 10 times the amount of COD components.

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