Wastewater treatment method

Abstract

To provide a new wastewater treatment method capable of treating wastewater with high COD values in a short time.SOLUTION: It is a method for treating wastewater by adding sodium persulfate and sodium sulfate or gypsum to the wastewater and heating it to 85°C or higher, in which the amount of sodium persulfate added is 40% or more of the amount necessary to achieve a COD removal rate of 99% or more when sodium persulfate alone is used. Preferably, the amount of sodium persulfate added is less than 60% of the amount required to achieve a COD removal rate of 99% or more when sodium persulfate alone is used.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for treating wastewater having a high COD value. [Background technology]

[0002] According to Article 3, Paragraph 1 of the Water Pollution Control Act and the Ministerial Ordinance Prescribing Effluent Standards, the allowable limit for chemical oxygen demand (COD) in effluent water is 160 mg / L. Conventionally, wastewater with a high COD value significantly exceeding this allowable limit has been treated by combining multiple processes to meet the effluent standards. For example, treatment has been carried out by selecting and combining multiple appropriate processes from among activated sludge treatment using microorganisms, coprecipitation using coagulants, membrane separation, oxidation decomposition using catalysts and light, treatment using single or multiple oxidizing agents, and treatment using a combination of oxidizing agents and catalysts. This has resulted in long treatment times and increased treatment costs. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-314880 Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, an object of the present invention is to provide a new method for treating wastewater that can treat wastewater having a high COD value in a short period of time. [Means for solving the problem]

[0005] The present inventors have conducted extensive research into treating wastewater with a high COD value in a short period of time, and have found that when sodium persulfate and then sodium sulfate were added to simulated phenol-containing wastewater with a high COD value, the COD value was reduced extremely efficiently with a smaller amount of sodium persulfate added compared to the case where only sodium persulfate was added, thereby arriving at the present invention.

[0006] That is, the method for treating wastewater of the present invention is a method for treating wastewater in which sodium persulfate and sodium sulfate or gypsum are added to the wastewater and the resulting mixture is heated to 85°C or higher, and the amount of sodium persulfate added is 40% or more of the amount required to achieve a COD removal rate of 99% or higher when treatment is performed at 95°C using sodium persulfate alone.

[0007] In addition, the amount of sodium persulfate added is set to 60% or less of the amount required to achieve a COD removal rate of 99% or more when treated at 95°C using only sodium persulfate.

[0008] In addition, the amount of sodium sulfate to be added shall be at least 0.5 g of anhydrous sodium sulfate per 100 ml of wastewater.

[0009] In addition, the amount of gypsum to be added shall be at least 1 g of hemihydrate gypsum per 100 ml of wastewater.

[0010] The method for treating wastewater according to claim 1, further comprising adding sodium sulfate and gypsum. [Effects of the Invention]

[0011] According to the wastewater treatment method of the present invention, wastewater having a high COD value can be treated in a single step in a short time. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the change in the amount of sodium persulfate added and the COD removal rate when only sodium persulfate is added in an example of the present invention. [Figure 2]10 is a graph showing the change in COD removal rate and the amount of anhydrous sodium sulfate added when 5 g of sodium persulfate was added. [Figure 3] 10 is a graph showing the change in COD removal rate and the amount of anhydrous sodium sulfate added when 3 g of sodium persulfate was added. [Figure 4] 10 is a graph showing the change in the amount of hemihydrate gypsum added and the COD removal rate when 4 g of sodium persulfate and 3 g of anhydrous sodium sulfate are added. DETAILED DESCRIPTION OF THE INVENTION

[0013] The wastewater treatment method of the present invention involves adding sodium persulfate (NaSO) and sodium sulfate (NaSO) or gypsum (CaSO) to wastewater and heating the mixture to 85°C or higher. The amount of sodium persulfate added is at least 40% of the amount required to achieve a chemical oxygen demand (COD) removal rate of 99% or higher when treated at 95°C using sodium persulfate alone. Furthermore, by setting the heating temperature to 85°C or higher, treatment is completed within four hours. Note that temperatures below 85°C are undesirable because they require a long treatment time.

[0014] According to the wastewater treatment method of the present invention, the amount of sodium persulfate added is set to at least 40% of the amount required to achieve a COD removal rate of at least 99% when sodium persulfate alone is used at 95°C, and sodium sulfate or gypsum is used in combination, thereby reducing the amount of expensive sodium persulfate added, thereby reducing treatment costs and enabling extremely efficient removal of COD from the wastewater. Therefore, when treating wastewater with a high COD value, there is no need to combine the method with other treatment methods.

[0015] Note that adding more sodium persulfate than necessary does not increase the effect. Therefore, in order to reduce the amount of expensive sodium persulfate added and thereby reduce the cost of treatment, it is preferable to set the amount of sodium persulfate added to less than 60% of the amount required to achieve a COD removal rate of 99% or more when treatment is carried out at 95°C using only sodium persulfate.

[0016] Furthermore, according to the wastewater treatment method of the present invention, it is possible to achieve a COD removal rate of approximately 90% or more, and even 99% or more under certain conditions. The COD removal rate refers to the percentage of the COD value removed by treatment relative to the COD value of the wastewater before treatment. For example, if the COD value of the wastewater before treatment is 19,000 mg / L and the COD value of the wastewater after treatment is 190 mg / L, the COD removal rate is 99%.

[0017] The amounts of sodium sulfate and gypsum added are not limited to specific amounts and may be adjusted appropriately depending on the COD value of the wastewater to be treated. For example, in order to efficiently reduce the COD value, the amount of sodium sulfate added may be 0.5 g or more per 100 ml of wastewater as anhydrous sodium sulfate, and the amount of gypsum added may be 1 g or more per 100 ml of wastewater as gypsum hemihydrate.

[0018] The wastewater treatment method of the present invention can obtain the same effect regardless of whether sodium persulfate and sodium sulfate are added, whether sodium persulfate and gypsum are added, or whether sodium persulfate, sodium sulfate, and gypsum are added. It is believed that sodium persulfate acts as an oxidizing agent, and sodium sulfate or gypsum acts as an auxiliary oxidation agent.

[0019] As described above, the wastewater treatment method of the present invention can treat wastewater in a single-stage addition process, thereby simplifying wastewater treatment. Furthermore, since there is little residue left after wastewater treatment, the residue treatment step can be omitted. This makes it possible to save labor in wastewater treatment and reduce treatment costs.

[0020] The following provides a detailed description of examples of the method and agent for treating wastewater having a high COD value according to the present invention. However, the present invention is not limited to the following examples, and various modifications are possible. [Example]

[0021] [Chemicals used] In this example, the following chemicals were used: Phenol: Fujifilm Wako Pure Chemical Industries, Ltd. (special grade) Sodium persulfate (Na2S2O8): Mitsubishi Gas Chemical Company, Inc. Anhydrous sodium sulfate (Na2SO4): Showa Chemical Co., Ltd. (Grade 1) Hemihydrate gypsum (CaSO4·0.5H2O): Kanto Chemical Co., Ltd. (Grade 1)

[0022] [Method of measuring COD value] The COD value was measured according to the method shown in JIS K0102:2016, "Oxygen consumption by potassium permanganate at 17.100°C (CODMn)."

[0023] The COD quantification range by this method is 0.5 to 11 mg / L, so samples with high COD values were diluted appropriately to fall within this range before measurement.

[0024] [Preparation of simulated wastewater] A simulated wastewater was prepared by adding 5.00 g of phenol to 500 ml of ion-exchanged water. The COD value of the simulated wastewater was 19,000 mg / L.

[0025] [Oxidation treatment of simulated wastewater] To 100 ml of the simulated wastewater prepared above, a specified amount of a treatment agent selected from anhydrous sodium sulfate, hemihydrate gypsum, or sodium persulfate, as shown in Tables 1 and 2, was added, and the mixture was heated in a water bath at the temperatures shown in Tables 1 and 2 to carry out oxidation treatment. The COD value of the simulated wastewater after oxidation treatment was measured. The results are shown in Tables 1 and 2.

[0026] [COD removal rate by oxidation treatment of simulated wastewater] The COD removal rate was calculated based on the COD values measured above. The results are shown in Tables 1 and 2.

[0027] Furthermore, Figure 1 shows the change in COD removal rate versus the amount of sodium persulfate added when only sodium persulfate was added, Figure 2 shows the change in COD removal rate versus the amount of anhydrous sodium sulfate added when 5 g of sodium persulfate was added, Figure 3 shows the change in COD removal rate versus the amount of anhydrous sodium sulfate added when 3 g of sodium persulfate was added, and Figure 4 shows the change in COD removal rate versus the amount of hemihydrate gypsum added when 4 g of sodium persulfate and 3 g of anhydrous sodium sulfate were added.

[0028] As shown in Figure 1, the COD value after oxidation treatment decreased linearly with increasing amounts of sodium persulfate added. Furthermore, Comparative Example 1 shown in Table 2 revealed that when treatment was performed at 95°C using only sodium persulfate, it was necessary to add 10 g of sodium persulfate to achieve a COD removal rate of 99% or more.

[0029] On the other hand, as shown in FIG. 2, when 5 g of sodium persulfate (50% of Comparative Example 1) was added, the COD value was significantly reduced by adding a small amount of sodium sulfate.

[0030] Furthermore, as shown in FIG. 3, when 3 g of sodium persulfate (30% of Comparative Example 1) was added, the COD value did not decrease significantly even when sodium sulfate was further added.

[0031] Furthermore, as shown in FIG. 4, when 4 g of sodium persulfate (40% of Comparative Example 1) and 3 g of anhydrous sodium sulfate were added and gypsum hemihydrate was added, a decrease in the COD value was observed.

[0032] In addition, in the other examples described above, it was found that the COD removal rate could be increased to approximately 90% or more when the amount of sodium persulfate added was increased to 4 g or more, which corresponds to 40% of the amount (10 g in Comparative Example 1) required to achieve a COD removal rate of 99% or more when treated at 95° C. using only sodium persulfate. Also, by adjusting the amount of anhydrous sodium sulfate or gypsum hemihydrate added, it was possible to increase the COD removal rate to 99% or more.

[0033] Furthermore, when the above simulated wastewater is subjected to oxidation treatment using only sodium persulfate, the theoretically required amount of sodium persulfate is estimated to be approximately 300 g / L, which corresponds to approximately 30 g per 100 ml of simulated wastewater. Therefore, in all Examples, a higher than expected COD reduction effect was observed even with a small amount of sodium persulfate added, and the effect was more pronounced when anhydrous sodium sulfate or gypsum hemihydrate was also added.

[0034] [Table 1]

[0035] [Table 2]

Claims

1. A method for treating wastewater in which sodium persulfate and sodium sulfate or gypsum are added to the wastewater and the resulting mixture is heated to 85°C or higher, characterized in that the amount of sodium persulfate added is 40% or more of the amount required to achieve a COD removal rate of 99% or higher when treatment is performed at 95°C using sodium persulfate alone.

2. 2. The method for treating wastewater according to claim 1, wherein the amount of sodium persulfate added is less than 60% of the amount required to achieve a COD removal rate of 99% or more when sodium persulfate alone is used.

3. 2. The method for treating wastewater according to claim 1, wherein the amount of sodium sulfate added is 0.5 g or more in terms of anhydrous sodium sulfate per 100 ml of wastewater.

4. 2. The method for treating wastewater according to claim 1, wherein the amount of gypsum added is 1 g or more in terms of gypsum hemihydrate per 100 ml of wastewater.

5. 2. The method for treating wastewater according to claim 1, wherein sodium sulfate and gypsum are added.

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