Wastewater treatment methods

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 Art

[0002] According to Article 3, Paragraph 1 of the Water Pollution Control Law and the ordinance establishing effluent standards, the allowable limit of the chemical oxygen demand (COD) in the discharged water is set at 160 mg / L. Conventionally, when treating wastewater having a high COD value greatly exceeding this allowable limit, in order to meet the effluent standards, treatment has been performed by combining a plurality of processes. For example, treatment has been performed by selecting and combining a plurality of appropriate processes from among activated sludge treatment by microorganisms, coprecipitation method using a flocculant, membrane separation method, oxidative decomposition method using a catalyst and light, single or multiple oxidant addition treatment methods, treatment methods using a combination of an oxidant and a catalyst, etc. For this reason, the treatment time has become long, and an increase in the cost related to treatment has been a problem.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems 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 time.

Means for Solving the Problems

[0005] The inventors diligently studied how to treat wastewater with high COD values ​​in a short time. They discovered that when sodium persulfate was added to simulated phenol-containing wastewater with high COD values, and then sodium sulfate was added, the COD value decreased extremely efficiently with a smaller amount of sodium persulfate compared to when only sodium persulfate was added, leading to the present invention.

[0006] In other words, the wastewater treatment method of the present invention is a wastewater treatment method in which sodium persulfate and sodium sulfate or gypsum are added to the wastewater and heated to 85°C or higher, wherein 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 treating at 95°C using only sodium persulfate.

[0007] Furthermore, the amount of sodium persulfate added should be 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] Furthermore, the amount of sodium sulfate added should be 0.5 g or more per 100 ml of wastewater as anhydrous sodium sulfate.

[0009] Furthermore, the amount of gypsum added should be 1g or more per 100ml of wastewater as hemihydrate gypsum.

[0010] Furthermore, the wastewater treatment method according to claim 1, wherein sodium sulfate and gypsum are added. [Effects of the Invention]

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

[0012] [Figure 1] This graph shows the change in the amount of sodium persulfate added and the COD removal rate when only sodium persulfate is added in an embodiment of the present invention. [Figure 2]The graph above shows the change in COD removal rate and the amount of anhydrous sodium sulfate added when 5g of sodium persulfate is added. [Figure 3] The graph above shows the change in COD removal rate and the amount of anhydrous sodium sulfate added when 3g of sodium persulfate is added. [Figure 4] The graph above shows the change in the amount of hemihydrate gypsum added and the COD removal rate when 4g of sodium persulfate and 3g of anhydrous sodium sulfate are added. [Modes for carrying out the invention]

[0013] The wastewater treatment method of the present invention involves adding sodium persulfate (Na2S2O8) and sodium sulfate (Na2SO4) or gypsum (CaSO4) to the wastewater and heating it to 85°C or higher. Here, the amount of sodium persulfate added is 40% or more of the amount required to achieve a chemical oxygen demand (COD) removal rate of 99% or more when treated at 95°C using only sodium persulfate. Furthermore, by heating the temperature to 85°C or higher, the treatment can be completed within 4 hours. It should be noted that temperatures below 85°C are undesirable because they require a long time for treatment.

[0014] According to the wastewater treatment method of the present invention, by adding sodium persulfate at a rate of 40% or more of the amount required to achieve a COD removal rate of 99% or more when treating at 95°C using only sodium persulfate, and by using sodium sulfate or gypsum in combination, the amount of expensive sodium persulfate added can be reduced, thereby lowering the treatment costs, while also removing COD from wastewater very efficiently. Therefore, when treating wastewater with high COD values, there is no need to combine it with other treatment methods.

[0015] Furthermore, since adding more sodium persulfate than necessary does not change the effect, in order to reduce the amount of expensive sodium persulfate added and lower the treatment costs, it is preferable to add less than 60% of the amount necessary to achieve a COD removal rate of 99% or more when treating 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, but should be adjusted as appropriate according to the COD value of the wastewater being treated. For example, 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 hemihydrate gypsum.

[0018] The wastewater treatment method of the present invention can achieve the same effect in any case, whether sodium persulfate and sodium sulfate are added, sodium persulfate and gypsum are added, or sodium persulfate, sodium sulfate, and gypsum are added. It is thought that sodium persulfate acts as an oxidizing agent, and sodium sulfate or gypsum acts as an oxidizing aid.

[0019] Thus, the wastewater treatment method of the present invention can be performed in a single-step additive process, thus simplifying wastewater treatment. Furthermore, because there is little residue after wastewater treatment, the residue treatment process can be omitted. Therefore, it is possible to reduce labor and treatment costs in wastewater treatment.

[0020] Hereinafter, the treatment method and treatment agent for wastewater with a high COD value of the present invention will be specifically described. Note that the present invention is not limited by the following examples, and various modified implementations are possible.

Example

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

[0022] [Method for Measuring COD Value] The COD value was measured according to the method described in "17. Oxygen consumption by potassium permanganate at 100 °C (CODMn)" in JIS K0102:2016.

[0023] Since the quantification range of COD by this method is in the range of 0.5 to 11 mg / L, for samples with a high COD value, appropriate dilution was performed to bring them within this range before measurement.

[0024] [Preparation of Simulated Wastewater] 5.00 g of phenol was added to 500 ml of ion-exchanged water to prepare simulated wastewater. The COD value of the simulated wastewater was 19000 mg / L.

[0025] [Oxidation Treatment of Simulated Wastewater] To 100 ml of the simulated wastewater prepared above, the predetermined amounts shown in Tables 1 and 2 of the treatment agent selected from anhydrous sodium sulfate, hemihydrate gypsum, and sodium persulfate were added, and heated in a water bath at the temperatures shown in Tables 1 and 2 for 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] Based on the COD values ​​measured above, the COD removal rate was calculated. The results are shown in Tables 1 and 2.

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

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

[0029] On the other hand, as shown in Figure 2, when 5g of sodium persulfate (50% of that in Comparative Example 1) was added, the COD value decreased significantly with the addition of an even smaller amount of sodium sulfate.

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

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

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

[0033] Furthermore, when oxidizing the above simulated wastewater with sodium persulfate alone, the theoretical 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 surprisingly high COD reduction effect was observed even with a small amount of sodium persulfate added, and the effect was even more pronounced when anhydrous sodium sulfate or hemihydrate gypsum was added.

[0034] [Table 1]

[0035] [Table 2]

Claims

1. A method for treating wastewater, comprising adding sodium persulfate and sodium sulfate or gypsum to the wastewater and heating it to 85°C or higher, characterized in that 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 treating the wastewater at 95°C using only sodium persulfate.

2. The wastewater treatment method 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. The wastewater treatment method according to claim 1, wherein the amount of sodium sulfate added is 0.5 g or more per 100 ml of wastewater as anhydrous sodium sulfate.

4. The wastewater treatment method according to claim 1, wherein the amount of gypsum added is 1 g or more per 100 ml of wastewater as hemihydrate gypsum.

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

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