Wastewater treatment methods

Abstract

To provide a method designed for waste water containing cyanide ions and thiocyanate ions, the method using the activated sludge technique to effectively reduce the cyanide ions and thiocyanate ions in the waste water through a simplified process.SOLUTION: A method for treating waste water containing cyanide ions and thiocyanate ions is provided. The concentration of the thiocyanate ions in the waste water is 25 mg / L or more. The method includes: a first step for adding and reacting hydrogen peroxide with the waste water, to yield a reaction liquid; and a second step for flowing the reaction liquid from the first step into a biological treatment tank that accommodates activated sludge, to subject it to biological treatment.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for treating wastewater. Background Art

[0002] Coke, which is used to reduce iron oxide contained in iron ore in iron manufacturing, is produced by carbonizing coal in a coke oven. Gas generated during carbonization of coal (coke oven gas) is subjected to removal of impurities, recovery of components, heat and the like for reuse in a refining facility equipped with various devices. One example thereof is a step of cooling the coke oven gas and collecting impurities in the coke oven gas by spraying ammonia water onto the coke oven gas (flushing). Condensed water generated in this step (also referred to as "ammonia liquor" or "coke oven wastewater") contains COD (chemical oxygen demand) components.

[0003] In a coke oven wastewater (ammonia liquor) treatment facility, coke oven wastewater containing COD components is introduced into a biological treatment tank that accommodates activated sludge, and the COD components in the coke oven wastewater are decomposed and reduced by an activated sludge process. For example, Patent Document 1 discloses a method for treating coke plant wastewater, characterized in that coke plant wastewater is first subjected to ammonia removal treatment, then this treated liquid is subjected to coagulating sedimentation treatment by addition of a ferrous salt, and then activated sludge treatment is performed. Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Unexamined Patent Publication No. 2000-84589 Summary of the Invention Problem to be Solved by the Invention

[0005] Industrial wastewater such as coke oven wastewater in the above-described coke oven wastewater treatment facility contains cyanide ions (CN -;Also referred to as free cyanide.) may be present.As a result of the inventors' studies, in coke oven wastewater treatment equipment, thiocyanate ions (SCN) may be present as a COD component. - When treating coke oven wastewater containing ) by the activated sludge method, if the wastewater also contains cyanide ions, SCN - It was found that the treatment performance of activated sludge decreased in relation to this.

[0006] Therefore, the present invention aims to provide a simple method for effectively reducing cyanide ions and thiocyanate ions in wastewater containing cyanide ions and thiocyanate ions using the activated sludge method. [Means for solving the problem]

[0007] According to the present invention, a method for treating wastewater containing cyanide ions and thiocyanate ions is provided, comprising: a first step of adding hydrogen peroxide to the wastewater and reacting it to obtain a reaction solution, wherein the concentration of thiocyanate ions in the wastewater is 25 mg / L or more; and a second step of flowing the reaction solution obtained in the first step into a biological treatment tank containing activated sludge and performing biological treatment. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a simple method for effectively reducing cyanide ions and thiocyanate ions in wastewater containing cyanide ions and thiocyanate ions using the activated sludge method. [Modes for carrying out the invention]

[0009] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0010] As mentioned above, in coke oven wastewater treatment facilities, COD components in coke oven wastewater are decomposed and removed by the activated sludge method. On the other hand, wastewater such as coke oven wastewater contains cyanide ions (hereinafter referred to as "CN - It may be stated as ". ) may contain. As a result of our investigations, we have found that wastewater treated by the activated sludge method contains relatively high concentrations (e.g., 0.5 mg-CN / L or more) of CN. - It was found that the presence of thiocyanate ions (SCN), a type of COD component found in wastewater, reduces the treatment performance of activated sludge that decomposes COD components, leading to a problem of degraded treated water quality. - It is sometimes stated that the treatment performance of activated sludge that decomposes thiocyanate ions has decreased. This is thought to be because microorganisms such as bacteria that can decompose thiocyanate ions in activated sludge are sensitive to cyanide toxicity and grow slowly, so it takes a long time for them to recover when they are damaged by cyanide ions.

[0011] Regarding wastewater treatment methods that contain both cyanide ions and thiocyanate ions, it is difficult to say that a stable and simple method for removing COD components has been established to date. Therefore, the inventors investigated a simple method to effectively reduce cyanide ions and thiocyanate ions in wastewater containing cyanide ions and thiocyanate ions using the activated sludge method. First, the inventors considered that in order to enable stable treatment to reduce cyanide ions and thiocyanate ions in wastewater, it is effective to reduce the cyanide ions in the wastewater before the wastewater flows into the biological treatment tank containing activated sludge. Furthermore, when reducing cyanide ions in the wastewater in the stage before the biological treatment tank, it was considered necessary to use a material that is less likely to damage the activated sludge in the biological treatment tank afterward.

[0012] Based on the above considerations, the present inventors have found a simple method that can effectively reduce cyanide ions and thiocyanate ions in wastewater containing cyanide ions and thiocyanate ions. Specifically, a wastewater treatment method according to one embodiment of the present invention (hereinafter sometimes referred to as "this method") includes a first step of adding hydrogen peroxide to the wastewater and reacting it to obtain a reaction solution, and a second step of flowing the reaction solution obtained in the first step into a biological treatment tank containing activated sludge and performing biological treatment.

[0013] The wastewater to be treated by this method is not particularly limited, as long as it contains cyanide ions and thiocyanate ions, with a thiocyanate ion concentration of 25 mg / L or higher. The inventors' research has shown that in order to reduce the cyanide ion concentration in the wastewater, thiocyanate ions must be present in the wastewater at a concentration of 25 mg / L or higher. Examples of such wastewater include coke oven wastewater generated during the carbonization of coal in a coke oven. Coke oven wastewater includes condensate generated when exhaust gas discharged during the production of coke from coal is cooled, and may also be scrubber wastewater after treatment with a scrubber or the like.

[0014] The concentration of thiocyanate ions in the wastewater is preferably 25 mg / L or higher, more preferably 50 mg / L or higher, more preferably 100 mg / L or higher, and preferably 3000 mg / L or lower. The concentration of cyanide ions in the wastewater is preferably 0.5 to 200 mg / L. In addition to cyanide ions and thiocyanate ions, wastewater further containing ammonia, phenol (a type of COD component), etc. is preferable. The ratio of the mass of carbon atoms in thiocyanate ions in the wastewater to the mass of carbon atoms in organic matter other than thiocyanate ions in the wastewater is preferably 1:0 to 1:10.

[0015] In this method, in the first step, hydrogen peroxide is added to wastewater containing cyanide ions and 25 mg / L or more of thiocyanate ions to cause reaction, whereby a reaction solution with reduced cyanide ions in the wastewater can be obtained. This is because thiocyanate ion (SCN - ) reacts with hydrogen peroxide (H2O2) to generate an oxide of thiocyanate ion, which then reacts with highly toxic cyanide ion (CN - ) to convert it into a low-toxicity substance such as cyanate ion (CNO - ) (see the following reaction formula (1)). Although the clear reaction mechanism is not clear, it is considered that thiocyanate ions act like a catalyst, the concentration of thiocyanate ions does not change, and only cyanide ions are removed. The first step preferably includes generating cyanate ions in the reaction solution by adding hydrogen peroxide to wastewater and causing the reaction. 2SCN - +H2O2+CN - →CNO - +2SCN - +H2O (1)

[0016] In the reaction according to the above reaction formula (1), thiocyanate ions, which are one type of COD component, remain. However, in the present method, the first step of obtaining a reaction solution in which the above reaction is considered to occur is employed as a pre-stage treatment for a biological treatment tank that performs biological treatment by the activated sludge method. Then, in the present method, as the second step, the reaction solution obtained in the first step is flowed into a biological treatment tank containing activated sludge and subjected to biological treatment.

[0017] Even if residual hydrogen peroxide is added to the wastewater, it is rapidly decomposed in the biological treatment tank containing activated sludge, thus minimizing damage to the activated sludge. Therefore, the thiocyanate ions in the reaction solution necessary for the above reaction can be decomposed by the activated sludge in the biological treatment tank. Thus, in this method, the cyanide ions in the wastewater (reaction solution) flowing into the biological treatment tank containing activated sludge can be reduced by the simple operation of adding hydrogen peroxide to the wastewater and allowing it to react. As a result, the activated sludge is less susceptible to damage from cyanide ions, making it possible to obtain stable treatment performance for the decomposition of residual thiocyanate ions in the reaction solution flowing into the biological treatment tank using activated sludge. In order to decompose thiocyanate ions with activated sludge and reduce them more effectively, it is preferable to use activated sludge from a biological treatment tank that biologically treats wastewater containing COD components, that is, activated sludge that has the ability to decompose COD components.

[0018] As described above, when treating wastewater containing COD components using the activated sludge method, the presence of cyanide ions in the wastewater can reduce the treatment performance of the activated sludge that decomposes thiocyanate ions, a type of COD component. In contrast, this method involves adding hydrogen peroxide, a chemical that is less likely to damage the activated sludge used in the subsequent biological treatment, to wastewater containing cyanide ions and thiocyanate ions at a concentration of 25 mg / L or more, and allowing the reaction to occur to obtain a reaction solution. In this way, the cyanide ions in the wastewater (reaction solution) before it flows into the biological treatment tank are reduced, thereby reducing the toxicity of the treated water (reaction solution) to the activated sludge before it flows into the biological treatment tank. As a result, by introducing the reaction solution into the biological treatment tank and performing biological treatment, it is possible to stably reduce the thiocyanate ions in the reaction solution using the activated sludge method.

[0019] Here is the joint CN - Methods for treating wastewater containing cyanide components, such as the Prussian Blue Process, are known to be used for treating CN -In methods that convert CN into insoluble cyanide compounds, solid-liquid separation equipment such as sedimentation tanks is required to separate and remove the resulting insoluble cyanide compounds, which increases equipment costs. In contrast, in the first step of this method, solid-liquid separation equipment is not required, and the CN in the wastewater is converted by adding hydrogen peroxide. - It can be reduced. Also, CN - In wastewater treatment methods containing cyanide components, using conventionally used hypochlorous acid or copper compounds in conventional doses can toxicize activated sludge. Therefore, in this method, which involves biological treatment using activated sludge in a subsequent stage, it is preferable not to use hypochlorous acid. As for copper compounds, as will be described later, it has been found that they can function as nutrients for activated sludge if they can supply copper ions to the activated sludge in a specific small amount, so they may be used for that purpose.

[0020] From the viewpoint of further reducing cyanide ions in wastewater, it is preferable that the amount of hydrogen peroxide added to the wastewater in the first step is such that the molar ratio of H2O2 to cyanide ions in the wastewater is 0.5 or more. On the other hand, it is preferable that the amount of hydrogen peroxide added to the wastewater is such that the above molar ratio is 30.0 or less. Furthermore, if hydrogen peroxide used in the first step remains, it is preferable that the concentration of hydrogen peroxide flowing into the biological treatment tank be 500 mg / L or less.

[0021] The first step in obtaining the above-mentioned reaction solution is to add thiosulfate ions (S2O3) to the wastewater. 2- Preferably, the process involves reacting hydrogen peroxide in the presence of ) to obtain a reaction solution. When obtaining the reaction solution, if thiosulfate ions are present in the wastewater, as shown in the reaction equation (2) below, thiosulfate ions (S2O3 2- ) by cyanide ions (CN - ) is thiocyanate ion (SCN - This is because it is thought to be converted into thiocyanate ions. If thiocyanate ions are generated in the reaction solution by such a reaction, the generated thiocyanate ions can be decomposed by the activated sludge in the biological treatment tank. H2O2 + S2O3 2- →[H2O2·S2O32- ] * [H2O2·S2O3 2- ] * +CN - →SCN - +H2O+SO4 2- (2)

[0022] From the viewpoint of reacting hydrogen peroxide in the presence of thiosulfate ions, wastewater containing thiosulfate ions in addition to cyanide ions and thiocyanate ions is preferable. Furthermore, when reacting hydrogen peroxide in the presence of thiosulfate ions, it is preferable to add a thiosulfate that generates thiosulfate ions in water. That is, it is preferable to add a thiosulfate together with hydrogen peroxide to the wastewater in the first step to obtain the reaction solution. The reaction shown in reaction equation (2) is considered to be faster than the reaction shown in reaction equation (1) above. Therefore, if neither thiocyanate ions nor thiosulfate ions are sufficiently contained in the wastewater, or if thiocyanate ions are sufficiently contained but sufficient reaction time with hydrogen peroxide cannot be secured, it is more preferable to add a thiosulfate together with hydrogen peroxide to the wastewater.

[0023] For example, when the thiosulfate ion content in the wastewater is less than 0.5 molar ratio to cyanide ions, the reaction time when hydrogen peroxide is added to the wastewater without adding thiosulfate is preferably 1 to 24 hours, more preferably 4 to 18 hours, and even more preferably 8 to 12 hours. On the other hand, when thiosulfate ions are present in the wastewater in an amount of 0.5 or more molar ratio to cyanide ions, the reaction time when hydrogen peroxide is added is preferably 1 second to 24 hours, more preferably 30 seconds to 12 hours, and even more preferably 1 minute to 1 hour. Thus, from the viewpoint of reducing cyanide ions in the wastewater in a shorter time in the first step, it is preferable to obtain the above-mentioned reaction solution in the wastewater in the presence of an amount of thiosulfate ions in the wastewater such that the molar ratio to cyanide ions is 0.5 or more. The molar ratio of thiosulfate ions to cyanide ions in the wastewater is more preferably 1.0 or more, even more preferably 1.5 or more, and preferably 30.0 or less.

[0024] Examples of thiosulfates that can be used when adding thiosulfates to wastewater include sodium thiosulfate, sodium thiosulfate pentahydrate, potassium thiosulfate, magnesium thiosulfate, magnesium thiosulfate hexahydrate, ammonium thiosulfate, barium thiosulfate, barium thiosulfate hydrate, calcium thiosulfate, and calcium thiosulfate hexahydrate. One type of thiosulfate may be used alone, or two or more types may be used in combination.

[0025] In the first step, the temperature of the wastewater when hydrogen peroxide is added to the wastewater and reacted is preferably 4 to 90°C, and more preferably 10 to 80°C. Also, in the first step, the pH of the wastewater when hydrogen peroxide is added to the wastewater and reacted is preferably 5.0 to 11.0, and more preferably 7.0 to 10.0.

[0026] In the second step, which takes place in a biological treatment tank (also called an aeration tank) containing activated sludge, the reaction solution obtained in the first step is used as the water to be treated. The reaction solution, which is the water to be treated in the second step, is wastewater (water to be treated) from which cyanide ions have been reduced by the first step. Therefore, the activated sludge in the biological treatment tank in the second step is less susceptible to damage from cyanide ions, and it is possible to stably decompose thiocyanate ions in the water to be treated (reaction solution).

[0027] As mentioned above, the activated sludge used in the second step is preferably activated sludge from a biological treatment tank that biologically treats wastewater containing COD components, and more preferably activated sludge from a coke oven wastewater treatment facility that treats coke oven wastewater containing COD components. In other words, it is preferable to use activated sludge containing bacteria capable of decomposing COD components, and more preferably activated sludge containing at least bacteria capable of decomposing thiocyanate ions (thiocyanide-degrading bacteria). Furthermore, it is even more preferable that the activated sludge contains phenolide-degrading bacteria and the like in addition to thiocyanide-degrading bacteria.

[0028] Examples of biological treatment tanks containing activated sludge used in the second step include: a tank containing activated sludge; a tank containing activated sludge that has been settled; a tank containing activated sludge supported on a carrier that flows within the tank (e.g., sponge or plastic) (fluidized bed carrier type biological treatment tank); a tank in which activated sludge is fixed to a carrier (fixed carrier) within the tank (fixed bed carrier type biological treatment tank); a membrane type activated sludge tank equipped with a membrane separation device for separating activated sludge and treated water within a tank containing activated sludge; and so on. Furthermore, biological treatment with activated sludge may be carried out using two or more of the above-mentioned biological treatment tanks containing activated sludge in combination. For example, as described in Japanese Patent Application Publication No. 2020-78767, an activated sludge tank in which activated sludge has been settled within the tank may be used in combination with the above-mentioned fluidized bed carrier type biological treatment tank. Furthermore, the biological treatment using activated sludge may also be a multiphase activated sludge method (for example, a two-phase activated sludge method) in which wastewater is treated in a first biological treatment tank where dispersed bacteria reside, and the liquid treated in the first biological treatment tank (treated liquid) is treated in a second biological treatment tank containing activated sludge.

[0029] In this method, as one embodiment, it is preferable to supply copper ions at a concentration of 0.01 to 2 mg-Cu / L in the second step, as a copper equivalent concentration to the mixture of reaction liquid and activated sludge flowing into the biological treatment tank, and perform biological treatment. This is because, as a result of the inventors' investigations, it was found that thiocyan-degrading bacteria in activated sludge require copper ions when decomposing thiocyanate ions, and the above-mentioned amount of copper ions was found to function as a nutrient for the activated sludge. When biological treatment is performed by supplying copper ions at a concentration of 0.01 to 2 mg-Cu / L, the decomposition rate of thiocyanate ions in wastewater is increased compared to when biological treatment is performed without supplying any copper ions, and it is possible to improve the decomposition rate of thiocyanate ions by activated sludge.

[0030] To supply the above-mentioned specific amount of copper ions to the mixture of the reaction solution and activated sludge, a solution obtained by dissolving a copper compound that generates copper ions when dissolved in a solvent, or a copper compound that generates copper ions when added to the reaction solution, activated sludge, or the above mixture can be used. Among these, from the viewpoint of ease of use and ease of supplying copper ions to the activated sludge, it is preferable to supply copper ions to the above mixture using a solution obtained by dissolving a copper compound in a solvent to generate copper ions.

[0031] The above copper ions include copper(I) ions (Cu + ) and copper(II) ions (Cu 2+ ) may be either one or both. Therefore, at least one of the copper(I) compounds and copper(II) compounds can be used as the copper compound. Examples of the solvent include water; acids such as dilute hydrochloric acid and dilute sulfuric acid; bases such as aqueous ammonia; etc. Examples of the copper compound include copper(I) compounds such as copper(I) chloride, copper(I) oxide (cuprous oxide), copper(I) bromide, copper(I) acetate, and copper(I) sulfide; and copper(II) compounds such as copper(II) fluoride, copper(II) chloride, copper(II) bromide, copper(II) iodide, copper(II) sulfate, copper(II) nitrate, copper(II) acetate, and copper(II) oxide. One or more of these can be used. Among the copper compounds, copper(I) oxide, copper(II) chloride, and copper(II) sulfate are preferred.

[0032] The processing time (reaction time) in the second step is preferably 1 to 60 hours, more preferably 3 to 50 hours, and even more preferably 6 to 40 hours. The pH in the biological treatment tank in the second step is preferably 4.0 to 10.0, and more preferably 5.0 to 9.5. The water temperature in the biological treatment tank is preferably 10 to 45°C, and more preferably 15 to 40°C. The concentration of MLSS (activated sludge suspended solids) in the biological treatment tank is preferably 500 to 10000 mg / L.

[0033] In one embodiment of this method, after the second step by the activated sludge method, a mixture of treated water and activated sludge obtained by biological treatment of the treated water (reaction solution) may be obtained. In one embodiment of this method, it is preferable to further include a solid-liquid separation step after the second step in which the mixture is separated into solid and liquid components. Furthermore, it is preferable to return the activated sludge separated from the treated water by the solid-liquid separation step to the biological treatment tank as return sludge. This allows the second step to be carried out by the continuous activated sludge method and makes it easier to maintain the concentration of MLSS in the biological treatment tank within a certain range. It is also preferable to use the above-mentioned membrane-type activated sludge tank as the biological treatment tank and to perform the solid-liquid separation treatment in that tank.

[0034] Solid-liquid separation equipment can be used in the solid-liquid separation process. Examples of solid-liquid separation equipment include sedimentation tanks (also called sedimentation ponds), and filtration devices using microfiltration membranes and ultrafiltration membranes. By using these, solid-liquid separation treatments such as sedimentation separation and membrane separation can be performed. Therefore, the second step described above may be a biological treatment using a sedimentation-type activated sludge method in which a sedimentation tank is installed downstream of the biological treatment tank, or a biological treatment using a membrane-type activated sludge method in which a separation membrane is installed downstream of the biological treatment tank. Furthermore, as described above, the biological treatment using the membrane-type activated sludge method may be carried out using a membrane-type activated sludge tank in which a membrane separation device is installed in a tank containing activated sludge, thereby omitting the solid-liquid separation equipment downstream of the biological treatment. Activated sludge and treated water can be separated from the above mixed liquid using solid-liquid separation equipment such as sedimentation tanks and filtration devices. The activated sludge obtained by the solid-liquid separation treatment can be returned to the biological treatment tank and reused as returned sludge.

[0035] As detailed above, according to the wastewater treatment method of one embodiment of the present invention, it is possible to effectively reduce cyanide ions and thiocyanate ions in wastewater containing cyanide ions and thiocyanate ions in a simple manner using the activated sludge method. Specifically, in the first step of this method, hydrogen peroxide, which is an agent that does not easily damage the activated sludge used in the subsequent second step, is added to wastewater containing cyanide ions and thiocyanate ions of 25 mg / L or more and reacted with it, thereby obtaining a reaction solution in which the cyanide ions in the wastewater have been reduced. In this way, the wastewater before flowing into the biological treatment tank is made into a reaction solution with reduced toxicity to the activated sludge, and in the second step, this reaction solution is flowed into the biological treatment tank and biologically treated with activated sludge, making it possible to stably reduce the thiocyanate ions in the reaction solution. Therefore, this method, which targets the above reaction solution for biological treatment with activated sludge, can increase the rate of COD decomposition by the decomposition of thiocyanate ions and provide a stabilizing effect on the decomposition of COD components compared to the case where the above wastewater is directly targeted for biological treatment with activated sludge.

[0036] Furthermore, the wastewater treatment method of one embodiment of the present invention can have the following configuration. [1] A method for treating wastewater containing cyanide ions and thiocyanate ions, The concentration of thiocyanate ions in the wastewater is 25 mg / L or more. The first step involves adding hydrogen peroxide to the wastewater and allowing it to react to obtain a reaction solution. A method for treating wastewater, comprising: a second step of introducing the reaction solution obtained in the first step into a biological treatment tank containing activated sludge and performing biological treatment. [2] The wastewater treatment method according to [1] above, wherein the wastewater further contains thiosulfate ions. [3] The wastewater treatment method according to [1] or [2] above, wherein in the first step, a thiosulfate is added to the wastewater together with hydrogen peroxide to obtain the reaction solution. [4] A method for treating wastewater according to any one of [1] to [3] above, wherein in the first step, the reaction solution is obtained in the wastewater in the presence of thiosulfate ions in an amount such that the molar ratio to cyanide ions is 0.5 or more. [5] The wastewater treatment method according to any one of [1] to [4] above, wherein the amount of hydrogen peroxide added to the wastewater in the first step is such that the molar ratio of hydrogen peroxide to cyanide ions in the wastewater is 0.5 or more. [6] The wastewater treatment method according to any one of the above [1] to [5], wherein the concentration of cyanide ions in the wastewater is 0.5 to 200 mg / L. [7] A method for treating wastewater according to any of [1] to [6] above, wherein the wastewater is coke oven wastewater. [Examples]

[0037] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0038] <Measurement method> (T-CN concentration) In the following test examples, the total cyanide (T-CN) concentration was analyzed by the picric acid method using a total cyanide analyzer (manufactured by Kyoritsu Chemical Laboratory Co., Ltd.; including a simple distillation kit, equipment, and reagent (LR-CN-T)). Specifically, a dilution series was prepared by diluting an aqueous KCN solution (1 g-CN / L) with water. The absorbance of the recovered solution after distillation was measured at a wavelength of 500 nm. As a result, a linear calibration curve was obtained in the range of 0 to 5 mg-CN / L. For the measurement samples in the test examples described below, the cyanide concentration was diluted to the range of 0 to 5 mg-CN / L, and a colorimetric test was performed using the method described above. From the obtained absorbance values, the total cyanide (T-CN) concentration (mg-CN / L) was calculated from the calibration curve.

[0039] (CNO - concentration) In the following preliminary test example, cyanate ion (CNO) -The concentration was measured by ion chromatography. During measurement, anions were separated using a high-speed ion chromatograph (product name "IC-2010", manufactured by Tosoh Techno Systems Co., Ltd.) and a suppressor gel (product name "TSKgel suppress IC-A", manufactured by Tosoh Techno Systems Co., Ltd.). A 1 g-CNO / L sodium cyanate solution was prepared and diluted with water to create a dilution series. As a result, a linear calibration curve was obtained from the peak area values ​​in the range of 0 to 50 mg-CNO / L. In a preliminary test example, the measurement sample was analyzed using the above method, and the presence or absence of cyanate ion generation was confirmed by whether or not a peak was present at the same retention time as when the calibration curve was created. If the presence of the above peak confirmed the generation of cyanate ions, the cyanate ion (CNO) was determined from the calibration curve based on the peak area value obtained during the analysis of the measurement sample. - The concentration (mg / L) was calculated.

[0040] (COD Mn ) According to the method specified in JIS K0102, the amount of oxygen consumed by potassium permanganate at 100°C (COD) Mn ) was calculated.

[0041] <Example of preliminary examination 1> In each of the preliminary test examples 1-1 to 1-5, thiocyanate ions (SCN) are used as wastewater. - A simulated wastewater sample 1 was prepared to resemble coke oven wastewater when it contained the specified components. Specifically, 100 mL of simulated wastewater sample 1 was prepared for each preliminary test example 1 by mixing and dissolving the components shown in the left column of Table 1 in 100 mL of water to the concentrations shown in the right column.

[0042] TIFF0007927649000001.tif39170

[0043] (Preliminary Examination Example 1-1) 100 mL of simulated wastewater 1 was placed in a polyethylene container (hereinafter simply referred to as "container"), and hydrogen peroxide was added to it to a final concentration of 50.0 mg / L. Then, the lid of the container was closed, and the liquid inside the container was mixed with a magnetic stirrer for 480 minutes in a constant temperature room at 30°C to obtain a reaction solution. A portion of the reaction solution was taken, and the T-CN concentration was measured.

[0044] (Preliminary Examination Example 1-2) 100 mL of simulated wastewater 1 is placed in a container, and sodium thiocyanate (NaSCN) aqueous solution is added to it so that the thiocyanate ion concentration (SCN concentration) becomes 10.0 mg-SCN / L. - The mixture contained ). Next, hydrogen peroxide was added to the container to a final concentration of 50.0 mg / L. The container lid was then closed, and the liquid in the container was mixed with a magnetic stirrer for 480 minutes in a constant temperature room at 30°C to obtain a reaction solution. A portion of the reaction solution was taken, and the T-CN concentration was measured.

[0045] (Preliminary examination examples 1-3, 1-4, 1-5) In preliminary test examples 1-3, 1-4, and 1-5, the procedure was the same as in preliminary test example 1-2, except that the amount of NaSCN aqueous solution added was changed to an amount that resulted in SCN concentrations of 25.0 mg-SCN / L, 50.0 mg-SCN / L, and 150.0 mg-SCN / L, respectively. A portion of the reaction solution obtained in each preliminary test example was taken, and the T-CN concentration was measured.

[0046] T-CN concentration (mg-CN / L) and CNO in preliminary test examples 1-1 to 1-5 - The measurement results for concentration (mg / L) are shown in Table 2. Table 2 shows the test conditions for preliminary test examples 1-1 to 1-5, specifically the CN in simulated wastewater 1. - The concentrations (mg-CN / L) and SCN concentrations (mg-SCN / L), as well as the final concentration of hydrogen peroxide (H2O2) added to simulated wastewater 1, are also shown.

[0047] TIFF0007927649000002.tif59170

[0048] Based on the results of preliminary test example 1, in preliminary test examples 1-1 and 1-2, in which hydrogen peroxide was added to simulated wastewater with a thiocyanate ion concentration of 10 mg / L or less, the resulting reaction solution showed a reduction in T-CN concentration and CNO - The formation of was not observed. On the other hand, in preliminary test examples 1-3 to 1-5, in which hydrogen peroxide was added to simulated wastewater containing 25 mg / L or more of thiocyanate ions, a reduction in T-CN concentration and CNO were observed in the resulting reaction solution. - The formation of [a certain substance] was observed. From these results, it was found that in order to reduce the amount of cyanide ions in wastewater containing cyanide ions and thiocyanate ions by adding hydrogen peroxide and reacting it, thiocyanate ions must be present in the wastewater at a concentration of 25 mg / L or higher.

[0049] <Test Example A Series> As part of the Test Example A series, Examples A1 to A8, Comparative Example A1, and Reference Example A were carried out as described below. In each of these Test Example A series, cyanide ions (CN) were further used as wastewater. - ), or CN - and thiosulfate ions (S2O3 2- A simulated wastewater 2 was prepared to resemble coke oven wastewater when both of the above were included. Specifically, the components shown in the left column of Table 3 were mixed and dissolved in 100 mL of water to the concentrations shown in the right column, and 100 mL of simulated wastewater 2 was prepared for use in each test example.

[0050] TIFF0007927649000003.tif36170

[0051] (Examples A1-A3) 100 mL of simulated wastewater 2 is placed in a container, and potassium cyanide (KCN) is added to the simulated wastewater 2 in the container to a concentration of 3.0 mg-CN / L (see the CN concentration shown in the test conditions column for step 1 in Table 4). -The container was then treated with 50.0 mg / L of hydrogen peroxide (H2O2) (see the amount of H2O2 shown in the Test Conditions column for Step 1 in Table 4). The pH of the liquid in the container immediately after adding hydrogen peroxide was 8.0. Next, the container was closed, and the first step was performed in a constant temperature room at 30°C, in which the liquid in the container was mixed with a magnetic stirrer for the reaction time shown in the Test Conditions column for Step 1 in Table 4 to obtain a reaction solution. A portion of the reaction solution was taken, and the T-CN concentration was measured.

[0052] 90 mL of the resulting reaction solution was transferred to a shaking Erlenmeyer flask (hereinafter simply referred to as "flask"). 10 mL of return sludge (MLSS (activated sludge suspended solids) concentration = 10,000 mg / L) collected from an aquatic water treatment facility equipped with a biological treatment tank containing activated sludge was added to this flask (MLSS concentration in the flask = 1,000 mg / L). Immediately after adding the activated sludge, the pH of the liquid in the flask was 8.0. The liquid in the flask was subjected to biological treatment (second step) for 47 hours while aerobic shaking at 30°C. 1 mL of the liquid in the flask was collected at predetermined reaction times (0 minutes, 16 hours, 24 hours, 32 hours, 40 hours, and 47 hours), and the supernatant obtained by centrifugation of 1 mL of the collected liquid at 9,000 × g was used as the treatment solution for that predetermined reaction time. The COD of the obtained treatment solution was then measured. Mn (mg / L) was measured, and the COD was measured at reaction times of 32 hours and 40 hours, respectively. Mn From this, the COD decomposition rate (mg / L / Hr) was calculated using the following formula. COD decomposition rate (mg / L / Hr)=[COD 32H -COD 40H ] / 8(Hr) COD 32H : COD with a reaction time of 32 hours Mn (mg / L) COD 40H : COD with a reaction time of 40 hours Mn (mg / L)

[0053] (Reference example A) In Reference Example A, KCN was not added to simulated wastewater 2 (i.e., CN - The tests and measurements were performed using the same procedure as in Examples A1 to A3, except that (the substance was not included) and hydrogen peroxide was not added to simulated wastewater 2.

[0054] (Comparative Example A1) In comparative example A1, the addition of KCN resulted in CN - The tests and measurements were performed using the same procedure as in Examples A1 to A3, except that hydrogen peroxide was not added to simulated wastewater 2 containing [the substance].

[0055] (Examples A4-A8) Place 100 mL of simulated wastewater 2 into a container, and add KCN to the simulated wastewater 2 in the container so that the concentration becomes 3.0 mg-CN / L (refer to the CN concentration shown in the test conditions column for step 1 in Table 4). - It was made to contain. In addition, sodium thiosulfate (Na2S2O3) was added to the simulated wastewater 2 in the container so that the S2O3 concentration (mg-S2O3 / L) shown in the test conditions column for the first step in Table 4 was obtained, and thiosulfate ions (S2O3 2- The container was then treated with 50.0 mg / L of hydrogen peroxide (see the amount of H2O2 shown in the Test Conditions column for Step 1 in Table 4). The pH of the liquid in the container immediately after adding hydrogen peroxide was 8.0. Next, the container lid was closed, and the liquid in the container was mixed with a magnetic stirrer for 1 minute (see the reaction time shown in the Test Conditions column for Step 1 in Table 4) in a constant temperature room at 30°C to obtain the reaction solution. A portion of the reaction solution was taken, and the T-CN concentration was measured. The obtained reaction solution was then subjected to biological treatment (Step 2) in the same manner as in Step 2 described in Examples A1 to A3, and COD was measured. Mn The concentration (mg / L) was measured, and the COD decomposition rate (mg / L / Hr) was calculated.

[0056] As a result of the above Test Example A series, the T-CN concentration obtained in the first step and the COD decomposition rate obtained in the second step are shown in Table 4, along with an overview of the test conditions for the first step described above. In Table 4, "S2O3 / CN(mol / mol)" in the Test Conditions column for the first step refers to the CN contained in simulated wastewater 2. - S2O3 2- This is the molar ratio. Similarly, "H2O2 / CN (mol / mol)" represents the amount of CN contained in simulated wastewater 2. - This is the molar ratio of the amount of H2O2 added to the amount of .

[0057] TIFF0007927649000004.tif93170

[0058] In Examples A1 to A3, it was confirmed that the amount of cyanide ions contained in simulated wastewater 2 could be reduced by the first step, in which hydrogen peroxide was added to simulated wastewater 2 and reacted with it. Furthermore, in Examples A1 to A3, it was confirmed that the COD decomposition rate in the second step was higher compared to Comparative Example A1, in which hydrogen peroxide was not added, as a result of reducing cyanide ions in the first step.

[0059] As can be seen from the comparison between Reference Example A and Comparative Example A1, Comparative Example A1, in which cyanide ions were added to simulated wastewater 2, showed a significantly lower COD decomposition rate compared to Reference Example A, in which cyanide ions were not added to simulated wastewater 2. Furthermore, Examples A1 to A3, in which a first step of adding hydrogen peroxide to simulated wastewater 2 and reacting it was performed for 60 to 480 minutes prior to the biological treatment, showed a clearly higher COD decomposition rate compared to Comparative Example 1. This is because, in Examples A1 to A3, the first step of adding hydrogen peroxide to simulated wastewater 2 was performed before the second step of biological treatment using the activated sludge method. - Because it was reduced by hydrogen peroxide, CN - This is thought to be because the degree of toxic effects on activated sludge was reduced. Therefore, it can be said that if the cyanide ion content in wastewater is reduced to some extent before biological treatment, the COD decomposition performance in subsequent biological treatment can be greatly improved.

[0060] Furthermore, based on the results of Examples A4 to A8, CN was found in the simulated wastewater 2. - The amount of S2O3 such that its molar ratio to is 0.5 or greater. 2- By performing the first step in the presence of CN, a reduction in T-CN concentration and an improvement in the COD decomposition rate were observed, even with a very short reaction time in the first step. From these results, CN - and SCN - Wastewater containing S2O3 2- If present, in the first step CN - The time required to decompose it can be shortened, and even if the reaction time in the first step is very short, the COD decomposition rate in the second step can be improved to the extent that CN - It was found that this could reduce [the problem].

[0061] <Test Example B Series> As part of the Test Example B series, Examples B1 to B5 and Comparative Example B1, described below, were carried out. For each of these Test Example B series, simulated wastewater 3 was prepared to resemble coke oven wastewater. Specifically, 100 mL of simulated wastewater 3 was prepared for each test example by mixing and dissolving the components shown in the left column of Table 5 in 100 mL of water to the concentrations shown in the right column.

[0062] TIFF0007927649000005.tif43170

[0063] In Test Example B, the biological treatment in the second step was carried out under different conditions than those in Test Example A, assuming that simulated wastewater 3 was present in the influent water of the biological treatment tank at approximately 5% by volume.

[0064] (Examples B1-B3) 100 mL of simulated wastewater 3 is placed in a container, and the final concentration of the simulated wastewater 3 in the container is determined to be the "H2O2 amount" and "H2O2 / CN" (CN) shown in the test conditions column for the first step in Table 6. -Hydrogen peroxide was added in an amount corresponding to the molar ratio of H2O2 to 50. The pH of the liquid in the container immediately after adding hydrogen peroxide was 8.0. Next, the container lid was closed, and the first step was performed in which the liquid in the container was mixed with a magnetic stirrer for 480 minutes (see the reaction time shown in the test conditions column for the first step in Table 6) in a constant temperature room at 30°C to obtain the reaction solution. A portion of the reaction solution was taken, and the T-CN concentration was measured.

[0065] Next, the resulting reaction solution was mixed with activated sludge to a concentration of 5% by volume in the biological treatment reaction system in the second step, and biological treatment was carried out. Specifically, 5 mL of the reaction solution, 90 mL of simulated wastewater 2, and 5 mL of activated sludge (return sludge collected from the ammonia treatment facility; final MLSS concentration = 1,000 mg / L) were placed in a flask and mixed (this operation diluted the reaction solution 20-fold). The solution in the flask was cultured aerobically at 30°C with shaking and biological treatment (second step) was carried out for 47 hours. At predetermined reaction times (0 minutes, 16 hours, 24 hours, 32 hours, 40 hours, and 47 hours), 1 mL of the solution in the flask was taken, and the supernatant obtained by centrifugation of 1 mL of the taken solution with a centrifugal force of 9,000 × g was used as the treatment solution for that predetermined reaction time. The obtained treatment solution was then subjected to COD testing in the same manner as in Test Example A. Mn The concentration (mg / L) was measured and the COD decomposition rate (mg / L / Hr) was calculated. In addition, the initial T-CN concentration (mg / L) of the treatment solution was measured at the start of the biological treatment in the second step (0 minutes of the above reaction time).

[0066] (Examples B4, B5) 100 mL of simulated wastewater 3 is placed in a container, and the final concentration of the simulated wastewater 3 in the container is determined to be the "amount of S2O3" and "S2O3 / CN" (CN) as shown in the test conditions column for the first step in Table 6. - Add an amount of sodium thiosulfate (Na2S2O3) such that the molar ratio of S2O3 to thiosulfate is equal, and thiosulfate ions (S2O3) 2- ) was added. Then, the simulated wastewater 3 in the container was mixed with "H2O2 amount" and "H2O2 / CN" (CN -Hydrogen peroxide was added in an amount corresponding to the molar ratio of H2O2 to 5. The pH of the liquid in the container immediately after adding hydrogen peroxide was 8.0. Next, the container lid was closed, and the first step was performed in which the liquid in the container was mixed with a magnetic stirrer for 30 minutes (see the reaction time shown in the test conditions column for the first step in Table 6) in a constant temperature room at 30°C to obtain a reaction solution. A portion of the reaction solution was taken, and the T-CN concentration was measured. Furthermore, the obtained reaction solution was subjected to biological treatment (second step) in the same manner as the second step described in Examples B1 to B3 to obtain a treated solution, and then the COD of the treated solution was measured. Mn The concentration (mg / L) was measured, and the COD decomposition rate (mg / L / Hr) was calculated. In addition, as in Examples B1 to B3, the initial T-CN concentration (mg / L) of the treatment solution was measured at the start of the biological treatment in the second step (0 minutes of reaction time).

[0067] As a result of the above-mentioned Test Example B series, the T-CN concentration obtained in the first step, the initial T-CN concentration at the start of the second step, and the COD decomposition rate obtained in the second step are shown in Table 6, along with an overview of the test conditions for the first step described above.

[0068] TIFF0007927649000006.tif69170

[0069] Based on the results of Examples B1-B3, CN - Even in wastewater with a high content of CN, adding hydrogen peroxide to the wastewater resulted in a reduction in T-CN concentration and an improvement in the COD decomposition rate, and the amount of CN in the first step was reduced to the extent that it improved the COD decomposition rate in the second step. - It was found that it could reduce CN. From the results of Examples B4-B5, - The amount of S2O3 such that its molar ratio to is 0.5 or greater. 2- By performing the first step in the presence of [substance name], a reduction in T-CN concentration and an improvement in the COD decomposition rate were observed, even with a short reaction time in the first step.

Claims

1. A method for treating wastewater containing cyanide ions and thiocyanate ions, A first step is to add hydrogen peroxide to the wastewater and react it under conditions in which the thiocyanate ions are present in the wastewater at a concentration of 25 mg / L or more, thereby obtaining a reaction solution in which the cyanide ions in the wastewater are reduced and the thiocyanate ions remain. A wastewater treatment method comprising: a second step of introducing the reaction solution obtained in the first step, in which the thiocyanate ions remain, into a biological treatment tank containing activated sludge and biologically treating it to decompose the thiocyanate ions in the reaction solution with the activated sludge.

2. The wastewater treatment method according to Claim 1, wherein the first step is to add hydrogen peroxide to the wastewater and react it to generate cyanate ions in the reaction solution.

3. The wastewater treatment method according to Claim 1, wherein in the first step, hydrogen peroxide is added to the wastewater and reacted to remove only the cyanide ions from the cyanide ions and thiocyanate ions in the wastewater.

4. The wastewater treatment method according to claim 1, wherein the oxidizing agent added to the wastewater in the first step is only hydrogen peroxide.

5. The wastewater treatment method according to claim 1, wherein the concentration of hydrogen peroxide flowing into the biological treatment tank is 500 mg / L or less.

6. The wastewater treatment method according to claim 1, wherein the wastewater further contains thiosulfate ions.

7. The wastewater treatment method according to claim 1, wherein in the first step, a thiosulfate is added to the wastewater together with the hydrogen peroxide to obtain the reaction solution.

8. The wastewater treatment method according to claim 1, wherein in the first step, the reaction solution is obtained in the wastewater in the presence of thiosulfate ions in an amount such that the molar ratio to cyanide ions is 0.5 or more.

9. The wastewater treatment method according to claim 1, wherein the amount of hydrogen peroxide added to the wastewater in the first step is such that the molar ratio of hydrogen peroxide to cyanide ions in the wastewater is 0.5 or more.

10. The wastewater treatment method according to claim 1, wherein the concentration of cyanide ions in the wastewater is 0.5 to 200 mg / L.

11. The wastewater treatment method according to any one of claims 1 to 10, wherein the wastewater is coke oven wastewater.

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