Wastewater treatment method and wastewater treatment chemical

Abstract

To provide a simple method for treating wastewater containing thiocyanate ions and phenol, which can promote a decomposition of thiocyanate ions in the wastewater using activated sludge.SOLUTION: There is provided a wastewater treatment method for treating wastewater containing thiocyanate ions and phenol, the method including: biologically treating the wastewater by introducing the wastewater into a biological treatment tank containing activated sludge; and supplying at least one chemical selected from the group consisting of sulfite and bisulfite to the wastewater.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for treating wastewater and a chemical solution for treating wastewater. [Background technology]

[0002] Coke, which is used to reduce the iron oxide contained in iron ore in steelmaking, is produced by carbonizing coal in a coke oven. The gas generated during coal carbonization (coke oven gas) is refined in a facility equipped with various devices to remove impurities and recover components and heat for reuse. One example is a process in which ammonia water is sprayed onto the coke oven gas (flushing) to cool it and capture impurities in the coke oven gas. The condensed water generated in this process (also known as "ammonia water" or "coke oven wastewater") contains COD (chemical oxygen demand) components.

[0003] In coke oven wastewater (ammonia water) treatment facilities, coke oven wastewater containing COD components is introduced into a biological treatment tank containing activated sludge, and the COD components in the coke oven wastewater are decomposed and reduced by the activated sludge method. For example, Patent Document 1 discloses a method for treating coke plant wastewater, which first removes ammonia from the coke oven wastewater, then subjects the treated liquid to coagulation and sedimentation treatment by adding ferrous salt, and then treats it with activated sludge. Furthermore, Patent Document 2 discloses a wastewater treatment device that treats water to be treated, such as coke oven wastewater, and includes an activated sludge tank and a fluidized bed carrier tank that discharge the treated water as treated water, as well as a settling tank that settles the activated sludge dispersed in the treated water discharged from these tanks. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-84589 [Patent Document 2] Japanese Patent Publication No. 2020-78767 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, in coke oven wastewater treatment facilities, COD components contained in the wastewater are removed from the coke oven wastewater by biological treatment using activated sludge. However, as a result of the investigations by the present inventors, it was found that thiocyanate ions (SCN), one of the COD components, are present in the wastewater. - It has been found that when activated sludge contains phenol, the treatment performance of activated sludge against thiocyanate ions is likely to be insufficient because thiocyanate ions are a persistent substance, and the treatment performance of activated sludge against thiocyanate ions is likely to decrease due to the effects of toxicity of coexisting substances other than thiocyanate ions. This is thought to be due to the fact that the bacteria contained in activated sludge that can decompose thiocyanate ions (thiocyanate-decomposing bacteria) are weak against toxic substances and grow slowly. As a result of further investigations by the present inventors, it has been found that the treatment performance of activated sludge against thiocyanate ions is more likely to decrease when wastewater also contains phenol as a COD component.

[0006] Therefore, the present invention aims to provide a simple method for treating wastewater containing thiocyanate ions and phenol, which is capable of promoting the decomposition of thiocyanate ions in the wastewater by using activated sludge. [Means for solving the problem]

[0007] That is, the present invention provides a method for treating wastewater containing thiocyanate ions and phenol, which comprises biologically treating the wastewater by introducing the wastewater into a biological treatment tank containing activated sludge, and supplying at least one chemical selected from the group consisting of sulfites and bisulfites to the wastewater. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a simple method for treating wastewater containing thiocyanate ions and phenol, which can promote the decomposition of thiocyanate ions in the wastewater by using activated sludge. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0010] In coke oven wastewater (ammonia water) treatment facilities, COD components in the coke oven wastewater are removed using the activated sludge process. Among these COD components, thiocyanate ions are resistant to degradation and are sometimes insufficiently decomposed. This problem of reduced treatment performance due to insufficient degradation is thought to be due to the fact that bacteria in activated sludge capable of decomposing thiocyanate ions (thiocyanate-decomposing bacteria) are sensitive to toxic substances and grow slowly. Furthermore, the inventors' research has revealed that the activated sludge treatment performance for thiocyanate ions is likely to be reduced when the wastewater also contains phenol as a COD component.

[0011] The present inventors conducted research to provide a simple method for treating wastewater containing thiocyanate ions and phenol, which can promote the decomposition of thiocyanate ions in the wastewater using activated sludge. In their research, the inventors came up with the idea of ​​adding an agent capable of reducing the inhibition of thiocyanate-decomposing bacteria as a simple means for stabilizing the decomposition of thiocyanate ions in activated sludge. Based on this idea, the inventors conducted experiments and found that adding sulfite and / or bisulfite to wastewater containing phenol, a COD component, is effective in reducing the inhibition of thiocyanate decomposition caused by phenol, leading to the present invention.

[0012] A method for treating wastewater according to one embodiment of the present invention (hereinafter sometimes simply referred to as "the method") is a method for treating wastewater containing thiocyanate ions and phenol. The method includes biologically treating the wastewater by introducing the wastewater into a biological treatment tank containing activated sludge, and supplying the wastewater with at least one chemical selected from the group consisting of sulfites and bisulfites.

[0013] Furthermore, a chemical solution for wastewater treatment according to one embodiment of the present invention (hereinafter sometimes simply referred to as "chemical solution" or "this chemical solution") is a chemical solution used in a wastewater treatment method that involves biological treatment of wastewater containing thiocyanate ions and phenol by injecting the wastewater into a biological treatment tank containing activated sludge. This chemical solution is an aqueous solution containing, as a main component, at least one chemical selected from the group consisting of sulfites and bisulfites.

[0014] In this method, wastewater containing thiocyanate ions and phenol is biologically treated by flowing it into a biological treatment tank containing activated sludge, and at least one chemical selected from the group consisting of sulfite and bisulfite is supplied to the wastewater. As described below, the chemical may be added to the wastewater by adding it to the biological treatment tank into which the wastewater flows, or by adding it to the wastewater before it flows into the biological treatment tank. Thus, this method facilitates the decomposition of thiocyanate ions in wastewater by a simple method in which biological treatment is performed using an activated sludge method in the presence of sulfite and / or bisulfite in the wastewater. In other words, this method easily improves the thiocyanate ion decomposition capacity of the biological treatment tank, thereby enabling stable decomposition of thiocyanate ions using activated sludge.

[0015] The wastewater to be treated by this method is not particularly limited as long as it contains COD components including at least thiocyanate ions and phenol. One example of such wastewater is coke oven wastewater (ammonia water) generated during coal carbonization in a coke oven. Coke oven wastewater contains condensed water generated by cooling the exhaust gas emitted during the production of coke from coal, and may be scrubber wastewater after treatment in a scrubber or the like. Furthermore, these may be diluted with industrial water, river water, seawater, or the like until they reach a concentration suitable for biological treatment. In this specification, coke oven wastewater (ammonia water) includes the above-mentioned scrubber wastewater and diluted forms.

[0016] Since coke oven wastewater (ammonia water) is preferred as the wastewater, in addition to thiocyanate ions and phenol, ammonia, sulfide ions (S 2- ), and polysulfide ions (S n 2- ) and the like are preferred. The wastewater may contain other COD components in addition to thiocyanate ions and phenol. Furthermore, the wastewater may be pretreated before flowing into the biological treatment tank. For example, if the wastewater contains cyanide ions (CN) in addition to thiocyanate ions and phenol, - ), the wastewater may be treated to reduce the amount of cyanide ions in the wastewater.

[0017] The thiocyanate ions in wastewater are usually present in the form of ions, but the wastewater may also contain thiocyanic acid (HSCN) before dissociation into ions, or thiocyanates, such as sodium thiocyanate, ammonium thiocyanate, calcium thiocyanate, and potassium thiocyanate.

[0018] In one embodiment of the present method, thiocyanate ions (SCN) of the wastewater suitable for treatment are -) is preferably 20 to 1500 mg-SCN / L, more preferably 50 to 400 mg-SCN / L. In one embodiment of the present method, the phenol concentration of the wastewater suitable for treatment is preferably 1 to 1500 mg / L, more preferably 100 to 500 mg / L. In one embodiment of the present method, the COD concentration (COD Mn ) is preferably 100 to 6000 mg / L, more preferably 300 to 1000 mg / L.

[0019] In one embodiment of the present method, the pH of the wastewater to be treated is preferably 4 to 10, more preferably 4.5 to 9.5. Similarly, the temperature of the wastewater is preferably 10 to 70°C, more preferably 15 to 45°C.

[0020] The method includes biologically treating the wastewater by injecting the wastewater into a biological treatment tank containing activated sludge, and supplying the wastewater with at least one chemical selected from the group consisting of sulfites and bisulfites.

[0021] Examples of sulfites that can be suitably used as a drug include sodium sulfite (NaSO), ammonium sulfite ((NH)SO), calcium sulfite (CaSO), and potassium sulfite (KSO). Examples of bisulfites (also known as hydrogen sulfites) that can be suitably used as a drug include sodium hydrogen sulfite (NaHSO), ammonium hydrogen sulfite (NHHSO), calcium hydrogen sulfite (Ca(HSO)), and potassium hydrogen sulfite (KHSO). It is preferable to use at least one selected from the group consisting of sodium sulfite, ammonium sulfite, calcium sulfite, potassium sulfite, sodium hydrogen sulfite, ammonium hydrogen sulfite, calcium hydrogen sulfite, and potassium hydrogen sulfite. Of these, it is more preferable to use at least one selected from the group consisting of sodium sulfite and sodium hydrogen sulfite.

[0022] The form of the chemical agent when supplied to wastewater can be, for example, a powder or a solution. From the viewpoint of ease of supply to wastewater and ease of handling, it is preferable to use a chemical solution that is an aqueous solution containing water and at least one chemical agent selected from the group consisting of sulfites and bisulfites. More preferably, a chemical solution that is an aqueous solution containing the above-mentioned chemical agent as the main component is used. In this chemical solution, the main component refers to the component other than water in the chemical solution that is the component with the highest content among the components dissolved in water.

[0023] The total content (mass%) of sulfite and bisulfite in the chemical solution is preferably 1 to 65 mass%, more preferably 10 to 60 mass%, and even more preferably 20 to 50 mass%, based on the total mass of the chemical solution. The content (mass%) of water in the chemical solution is preferably 35 to 99 mass%, more preferably 40 to 90 mass%, and even more preferably 50 to 80 mass%, based on the total mass of the chemical solution. The chemical solution may also contain an acid or alkali to adjust the pH. For example, when calcium salts are used as sulfite and bisulfite, it is preferable to add a compound that increases the solubility of calcium salts in water, such as hydrochloric acid.

[0024] The amount of chemicals added to wastewater is not particularly limited. Since the suitable amount of chemicals added to wastewater is thought to vary depending on the operating conditions of the activated sludge facility (activated sludge tank), the state of the activated sludge, the properties of the wastewater, etc., it is preferable to select a suitable amount depending on these factors. In one aspect of the present method, the total concentration (concentration in SO3 equivalent) of sulfite and bisulfite added to wastewater is preferably 50 to 1000 mg SO3 / L, more preferably 60 to 900 mg SO3 / L, and even more preferably 70 to 800 mg SO3 / L.

[0025] In this method, at least one chemical selected from the group consisting of sulfite and bisulfite is supplied to the wastewater when biological treatment is performed by flowing the wastewater into a biological treatment tank containing activated sludge. Therefore, the chemical may be supplied to the wastewater by adding the chemical to the biological treatment tank into which the wastewater flows, by adding the chemical to the wastewater before it flows into the biological treatment tank, or by both. When adding the chemical to the biological treatment tank into which the wastewater flows, the chemical may be added to the wastewater, the activated sludge, or a mixture of the wastewater and activated sludge in the biological treatment tank.

[0026] As described above, in one aspect, the present method can include biological treatment by adding an agent to a biological treatment tank into which wastewater flows. In another aspect, the present method can include adding an agent to the wastewater before it flows into the biological treatment tank, and then flowing the wastewater with the agent added into the biological treatment tank to perform biological treatment.

[0027] Activated sludge is contained in a biological treatment tank (also called an aeration tank) into which wastewater flows. The biological treatment tank is a tank in which activated sludge decomposes COD components, including thiocyanate ions, in the wastewater. Activated sludge that decomposes COD components is cultivated in the biological treatment tank. After wastewater is introduced into the biological treatment tank, the wastewater is aerated, and the activated sludge dispersed in the wastewater can grow while decomposing the COD components. As the activated sludge, activated sludge in a biological treatment tank that biologically treats wastewater containing COD components in a wastewater treatment facility is preferably used, and activated sludge in a coke oven wastewater treatment facility that treats coke oven wastewater containing COD components is more preferably used. That is, activated sludge containing bacteria capable of decomposing COD components is preferably used, and activated sludge containing at least thiocyanate-decomposing bacteria is more preferably used.

[0028] Examples of biological treatment tanks containing activated sludge include tanks containing activated sludge within the tank; tanks containing activated sludge supported on carriers (e.g., sponges, plastics, etc.) that move within the tank (fluidized-bed carrier-type biological treatment tanks); tanks in which activated sludge is fixed on carriers (fixed carriers) fixed within the tank (fixed-bed carrier-type biological treatment tanks); and membrane-type activated sludge tanks in which a membrane separation device for separating activated sludge from treated water is provided within a tank containing activated sludge. Furthermore, for biological treatment using activated sludge, two or more of the above-mentioned biological treatment tanks containing activated sludge may be used in combination. For example, as described in Patent Document 2, an activated sludge tank containing activated sludge within the tank may be used in combination with the above-mentioned fluidized-bed carrier-type biological treatment tank. Furthermore, biological treatment using activated sludge may be a multiphase activated sludge method (e.g., a two-phase activated sludge method) in which wastewater is treated in a first biological treatment tank inhabited by dispersed bacteria, and the liquid (treated liquid) treated in the first biological treatment tank is treated in a biological treatment tank (second biological treatment tank) containing activated sludge.

[0029] The treatment time (reaction time) in the biological treatment tank 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 is preferably 4.0 to 10.0, and more preferably 4.5 to 9.5. The water temperature in the biological treatment tank is preferably 10 to 45°C, and more preferably 15 to 40°C.

[0030] In one embodiment of the present method, a mixed solution of treated wastewater (treated water) and activated sludge may be obtained after the steps of supplying sulfite and / or bisulfite to wastewater and biologically treating the wastewater with activated sludge in a biological treatment tank (hereinafter, sometimes simply referred to as the "biological treatment step"). In one embodiment, the present method preferably further comprises a solid-liquid separation step of separating the mixed solution into solids and liquids after the biological treatment step. It is also preferable that the activated sludge separated from the treated water in the solid-liquid separation step is returned to the biological treatment tank as returned sludge. This allows the biological treatment step to be performed using a continuous activated sludge method and makes it easier to maintain the MLSS (activated sludge suspended solids) concentration in the biological treatment tank within a certain range. The MLSS concentration in the biological treatment tank is preferably 500 to 10,000 mg / L. It is also preferable to use the above-mentioned membrane-type activated sludge tank as the biological treatment tank and perform solid-liquid separation within the tank.

[0031] A solid-liquid separation system can be used for the solid-liquid separation process. Examples of solid-liquid separation system include a settling tank (also called a settling pond) and a filtration system using a microfiltration membrane or an ultrafiltration membrane. Using these systems, solid-liquid separation processes such as sedimentation and membrane separation can be performed. Therefore, the above-mentioned biological treatment process may be a biological treatment using a settling activated sludge method in which a settling tank is installed downstream of a biological treatment tank, or a biological treatment using a membrane activated sludge method in which a separation membrane is installed downstream of a biological treatment tank. Furthermore, as described above, biological treatment using the membrane activated sludge method may be performed in a membrane activated sludge tank equipped with a membrane separation device in a tank containing activated sludge, thereby eliminating the need for a solid-liquid separation system downstream of the biological treatment. Alternatively, biological treatment may be performed using the membrane activated sludge tank equipped with a membrane separation device as the biological treatment tank. Activated sludge and treated water can be separated from the mixed liquid using solid-liquid separation system such as a settling tank or a filtration system. The activated sludge obtained by the solid-liquid separation treatment can be returned to the biological treatment tank and reused as returned sludge.

[0032] As described above in detail, this method involves biologically treating wastewater containing thiocyanate ions and phenol with activated sludge, and decomposing the thiocyanate ions in the wastewater through the activated sludge. Here, if the wastewater to be treated with activated sludge contains phenol, the activated sludge's ability to decompose thiocyanate ions is likely to be reduced. In this method, when the wastewater is introduced into a biological treatment tank containing activated sludge for biological treatment, at least one chemical selected from the group consisting of sulfite and bisulfite is supplied to the wastewater for biological treatment. This simple method can promote the decomposition of thiocyanate ions in the wastewater, even if the wastewater contains phenol. In other words, this method can easily improve the thiocyanate ion decomposition capacity of the biological treatment tank, thereby enabling the activated sludge to stably decompose thiocyanate ions.

[0033] As mentioned above, the inventors' investigations have revealed that when wastewater containing thiocyanate ions and phenols is biologically treated using activated sludge, phenols in the wastewater are believed to inhibit the decomposition of thiocyanate ions by activated sludge, i.e., to be a biological inhibitor. Furthermore, coke oven wastewater (ammonia water), which is a suitable wastewater, often contains sulfide ions and polysulfide ions, which are also thought to be biological inhibitors. It is believed that adding at least one chemical selected from the group consisting of sulfites and bisulfites to the wastewater can act on biological inhibitors such as phenols, thereby reducing their inhibitory effects. As a result, it is believed that the decomposition of thiocyanate ions in the wastewater can be promoted.

[0034] An embodiment of the present invention can have the following configuration. [1] A method for treating wastewater containing thiocyanate ions and phenol, comprising the steps of: The wastewater is subjected to biological treatment by being introduced into a biological treatment tank containing activated sludge; and A method for treating wastewater, comprising supplying at least one chemical selected from the group consisting of sulfites and bisulfites to the wastewater. [2] The method for treating wastewater according to [1] above, which comprises adding the agent to the biological treatment tank into which the wastewater flows to carry out the biological treatment. [3] A method for treating wastewater according to [1] or [2] above, which comprises adding the chemical to the wastewater before it flows into the biological treatment tank, and flowing the wastewater to which the chemical has been added into the biological treatment tank to carry out the biological treatment. [4] The method for treating wastewater according to any one of the above [1] to [3], wherein the wastewater is coke oven wastewater. [5] A wastewater treatment chemical solution used in a wastewater treatment method including biological treatment of wastewater containing thiocyanate ions and phenol by injecting the wastewater into a biological treatment tank containing activated sludge, A chemical solution for wastewater treatment that is an aqueous solution containing, as a main component, at least one chemical selected from the group consisting of sulfites and bisulfites. [Example]

[0035] Hereinafter, one embodiment of the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0036] <Measurement method> (Method for measuring thiocyanate ion concentration) In the following test examples, the thiocyanate ion concentration was measured by a colorimetric method using iron nitrate. Specifically, a sodium thiocyanate (NaSCN) aqueous solution (10 g-SCN / L) was diluted to prepare a dilution series of samples for a calibration curve. To 2 mL of each dilution series sample, 160 μL of a 2.5 mol / L nitric acid aqueous solution and 80 μL of an iron (II) nitrate aqueous solution were added to develop color. The absorbance at a wavelength of 460 nm immediately after color development was measured. This resulted in a linear calibration curve ranging from 0 to 30 mg-SCN / L. A spectrophotometer (trade name "Ratio Beam Spectrophotometer U-1800" manufactured by Hitachi, Ltd.) was used to measure the absorbance. The treated water obtained in the test examples described below was appropriately diluted with pure water to have a thiocyanate ion concentration in the range of 0 to 30 mg-SCN / L. The thiocyanate ion (SCN) concentration was calculated from the absorbance measured immediately after the color development procedure and the calibration curve. - ) concentration was calculated.

[0037] <Activated sludge> The following activated sludge A and activated sludge B were used. Activated sludge A: Return sludge collected from coke oven wastewater treatment facility A, which uses activated sludge to treat coke oven wastewater, was diluted with the supernatant water of the above return sludge to a sludge concentration of 17,600 mg-SS / L. Activated sludge B: Return sludge with a sludge concentration of 17,600 mg-SS / L collected from coke oven wastewater treatment facility B, which treats coke oven wastewater using activated sludge.

[0038] <Wastewater to be treated> Simulated wastewaters a1, a2, and b1 were prepared by dissolving the components shown in the upper section of Table 1 in a mixture of 120 mL of seawater and 20 mL of tap water shown in the lower section of Table 1. Simulated wastewater a1 was prepared to resemble the coke oven wastewater to be treated in coke oven wastewater treatment facility A. Simulated wastewater a2 was prepared to have a composition similar to that of simulated wastewater a1, except that phenol was removed from the composition. Simulated wastewater b1 was prepared to resemble the coke oven wastewater to be treated in coke oven wastewater treatment facility B. The "final concentration after mixing with activated sludge" shown in Table 1 refers to the final concentration of the mixture of simulated wastewater a1 or a2 with activated sludge A for simulated wastewater a1 and a2, and to the final concentration of the mixture of simulated wastewater b1 with activated sludge B for simulated wastewater b1.

[0039] TIFF2025130481000001.tif67170

[0040] <Preparation of drug solution> Sodium hydrogen sulfite as a chemical was dissolved in pure water to a concentration of 35 g / L (approximately 3.4% by mass) to prepare a bisulfite aqueous solution to be used as a chemical solution. Sodium sulfite as a chemical was also dissolved in pure water to a concentration of 35 g / L (approximately 3.4% by mass) to prepare a sulfite aqueous solution to be used as a chemical solution.

[0041] <Test Method> (Comparative Example A1) (1) 20 mL of activated sludge A was added to a shaker Erlenmeyer flask containing 140 mL of simulated wastewater a1. (2) Neither the aqueous sulfite solution nor the aqueous bisulfite solution was added to the shaken Erlenmeyer flask. (3) The above-mentioned shaker Erlenmeyer flask was shaken aerobically at 30°C. (4) Immediately after the start of shaking (0 hours) and 3 hours after the start of shaking, 1 mL of liquid was collected from the shaking Erlenmeyer flask, and this was centrifuged at 10,000 rpm for 1 minute. The resulting supernatant was used as treated water. (5) Thiocyanate ions (SCN) in each treated water - ) concentration was measured. (6) Using the measured thiocyanate ion concentration, calculate the thiocyanate ion (SCN) concentration based on the following formula: - The decomposition rate (mg / L / hr) of Decomposition rate of thiocyanate ion (mg / L / hr) = (C SCN,0 -C SCN,3 ) / 3 C SCN,0 : Thiocyanate ion concentration (mg / L) of treated water immediately after shaking started C SCN,3 : Thiocyanate ion concentration in treated water 3 hours after starting shaking (mg / L)

[0042] (Example A2) The test was carried out in the same manner as in Comparative Example A1, except that in (2) of the test method of Comparative Example A1, an aqueous bisulfite solution was added to a final concentration of 87.5 mg-SO3 / L.

[0043] (Example A3) The test was carried out in the same manner as in Comparative Example A1, except that in (2) of the test method of Comparative Example A1, an aqueous bisulfite solution was added to a final concentration of 175 mg-SO3 / L.

[0044] (Reference example A4) The test was carried out in the same manner as in Comparative Example A1, except that in (1) of the test method of Comparative Example A1, the simulated wastewater a1 was changed to the simulated wastewater a2.

[0045] (Reference example A5) The test was carried out in the same manner as in Comparative Example A1, except that in (1) of the test method for Comparative Example A1, the simulated wastewater a1 was changed to the simulated wastewater a2, and in (2) of the test method for Comparative Example A1, an aqueous bisulfite solution was added to a final concentration of 87.5 mg-SO3 / L.

[0046] (Comparative Example B1) A test was carried out in the same manner as in Comparative Example A1, except that in (1) of the test method of Comparative Example A1, activated sludge A and simulated wastewater a1 were changed to activated sludge B and simulated wastewater b1, respectively.

[0047] (Example B2) The test was conducted in the same manner as in Comparative Example A1, except that in (1) of the test method for Comparative Example A1, activated sludge A and simulated wastewater a1 were changed to activated sludge B and simulated wastewater b1, respectively, and in (2) of the test method for Comparative Example A1, an aqueous bisulfite solution was added to a final concentration of 350 mg-SO3 / L.

[0048] (Example B3) The test was conducted in the same manner as in Comparative Example A1, except that in (1) of the test method for Comparative Example A1, activated sludge A and simulated wastewater a1 were changed to activated sludge B and simulated wastewater b1, respectively, and in (2) of the test method for Comparative Example A1, an aqueous bisulfite solution was added to a final concentration of 700 mg-SO3 / L.

[0049] (Example B4) The test was conducted in the same manner as in Comparative Example A1, except that in (1) of the test method of Comparative Example A1, activated sludge A and simulated wastewater a1 were changed to activated sludge B and simulated wastewater b1, respectively, and in (2) of the test method of Comparative Example A1, an aqueous sulfite solution was added to a final concentration of 350 mg-SO3 / L.

[0050] (Example B5) The test was conducted in the same manner as in Comparative Example A1, except that in (1) of the test method of Comparative Example A1, activated sludge A and simulated wastewater a1 were changed to activated sludge B and simulated wastewater b1, respectively, and in (2) of the test method of Comparative Example A1, an aqueous sulfite solution was added to a final concentration of 700 mg-SO3 / L.

[0051] Table 2 shows an outline of the test conditions and results for the above Test Example A series (Comparative Example A1, Examples A2 and A3, and Reference Examples A4 and A5) and Test Example B series (Comparative Example B1, and Examples B2 to B5).

[0052] TIFF2025130481000002.tif93170

[0053] When simulated wastewater containing phenol (simulated wastewater a1) was used, the test examples (Examples A2 and A3) in which bisulfite was added at 87.5 mg SO3 / L or 175 mg SO3 / L showed a higher decomposition rate of thiocyanate ions than Comparative Example A1 in which no bisulfite was added. From these results, it can be said that in the case of the wastewater and activated sludge used in the test example A series, the addition of bisulfite had the effect of promoting the decomposition of thiocyanate ions by activated sludge.

[0054] On the other hand, when simulated wastewater not containing phenol (simulated wastewater a2) was used, no difference was observed in the decomposition rate of thiocyanate ions between the case where bisulfite was not added (Reference Example A4) and the case where bisulfite was added (Reference Example A5).

[0055] The results of Test Example A series suggest that the addition of bisulfite improves the decomposition rate of thiocyanate ions in activated sludge treatment of wastewater in the presence of both phenol and thiocyanate ions. While the reason for this effect is unclear, one possible explanation is that bisulfite reduces the toxic effects of phenol (which is known to be toxic to microorganisms despite its relatively good biodegradability). Based on these findings, this method is more suitable for use in cases where a certain level of phenol may be present in the biological treatment process of wastewater, such as when the inflow concentration of phenol in the wastewater is high or when the phenol-decomposing capacity of the activated sludge is reduced for some reason.

[0056] Even when activated sludge (activated sludge B) from a facility different from that of Test Example A series and simulated wastewater (simulated wastewater b1) with a composition different from that of Test Example A series were used, the decomposition rate of thiocyanate ions was shown to be higher when bisulfite was added (Examples B2 and B3) than when no bisulfite was added (Comparative Example B1).This result indicates that the addition of bisulfite has the effect of promoting the decomposition of thiocyanate ions.

[0057] In the Test Example B series, it was found that the decomposition rate of thiocyanate ions was higher when the bisulfite concentration was 700 mg-SO3 / L than when the bisulfite concentration was 350 mg-SO3 / L. Since the optimum bisulfite concentration may vary depending on the operating conditions of the activated sludge facility, the state of the activated sludge, the properties of the wastewater, etc., it was considered preferable to select an appropriate concentration depending on these factors.

[0058] Furthermore, when sulfite was used instead of bisulfite (Examples B3 and B4), the decomposition rate of thiocyanate ions was improved, similar to the case of using bisulfite. These results suggest that the addition of sulfite also promotes the decomposition of thiocyanate ions.

Claims

1. A method for treating wastewater containing thiocyanate ions and phenol, comprising the steps of: The wastewater is subjected to biological treatment by being introduced into a biological treatment tank containing activated sludge; and A method for treating wastewater, comprising supplying at least one chemical selected from the group consisting of sulfites and bisulfites to the wastewater.

2. The method for treating wastewater according to claim 1, further comprising adding the agent to the biological treatment tank into which the wastewater flows to perform the biological treatment.

3. 2. The method for treating wastewater according to claim 1, further comprising adding the chemical to the wastewater before it flows into the biological treatment tank, and then flowing the wastewater to which the chemical has been added into the biological treatment tank to perform the biological treatment.

4. 4. The method for treating wastewater according to claim 1, wherein the wastewater is coke oven wastewater.

5. A wastewater treatment chemical solution used in a wastewater treatment method including biological treatment of wastewater containing thiocyanate ions and phenol by injecting the wastewater into a biological treatment tank containing activated sludge, A chemical solution for wastewater treatment, which is an aqueous solution containing, as a main component, at least one chemical selected from the group consisting of sulfites and bisulfites.

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