Methods for treating wastewater, and nutrients for activated sludge

Abstract

To provide a method designed for waste water containing thiocyanate ions, the method using activated sludge to simply and stably degrade the thiocyanate ions.SOLUTION: A method for treating waste water includes a biological treatment step for flowing waste water containing thiocyanate ions into a biological treatment tank that accommodates activated sludge, to subject it to biological treatment. The biological treatment step is performed while supplying copper ions, serving as nutrients for the activated sludge, at a concentration of 0.01-2 mg-Cu / L, as a copper-equivalent concentration relative to the mixture of the wastewater and activated sludge flowing into the biological treatment tank.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for treating wastewater and a nutrient for activated sludge. [Background technology]

[0002] Coke, used in steelmaking to reduce iron oxide in iron ore, is produced by carbonizing coal in a coke oven. The gas generated during coal carbonization (coke oven gas) is purified in various equipment to remove impurities and recover components and heat for reuse. One example is the process of flushing the coke oven gas by spraying it with ammonia water to cool it and collect impurities. The condensate generated in this process (also called "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, characterized by first removing ammonia from the coke plant wastewater, then subjecting the treated liquid to coagulation and sedimentation treatment by adding ferrous salts, and finally treating it with activated sludge. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-84589 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described above, coke oven wastewater treatment facilities remove COD components from coke oven wastewater by biological treatment using activated sludge. However, as a result of our investigation, we found that thiocyanate ions (SCN), a type of COD component, are present in the wastewater. - When thiocyanate ions are present, it has been found that the treatment performance of activated sludge against COD components tends to decrease because thiocyanate ions are difficult to decompose. This is thought to be because the bacteria (thiocyan-degrading bacteria) that can decompose thiocyanate ions contained in activated sludge are sensitive to toxic substances and grow slowly.

[0006] Therefore, the present invention aims to provide a wastewater treatment method that allows for the simple and stable decomposition of thiocyanate ions in wastewater containing thiocyanate ions using activated sludge. [Means for solving the problem]

[0007] According to the present invention, a wastewater treatment method is provided, which includes a biological treatment step of introducing wastewater containing thiocyanate ions into a biological treatment tank containing activated sludge for biological treatment, wherein copper ions are supplied as a nutrient for the activated sludge at a concentration of 0.01 to 2 mg-Cu / L in terms of copper equivalent concentration relative to the mixture of the wastewater and the activated sludge flowing into the biological treatment tank, and the biological treatment step is carried out. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a wastewater treatment method that allows for the simple and stable decomposition of thiocyanate ions in wastewater containing thiocyanate ions using activated sludge. [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] In coke oven wastewater (ammonia water) treatment facilities, COD components are removed from coke oven wastewater using the activated sludge method. Among the COD components, thiocyanate ions (hereinafter referred to as "SCN") are removed. - It is sometimes written as "[...]. ) is a persistent substance, and occasionally its decomposition is not carried out sufficiently. This problem of reduced processing performance due to insufficient decomposition is thought to be due to the fact that bacteria capable of decomposing thiocyanate ions (thiocyan-degrading bacteria) are sensitive to toxic substances and have a slow growth rate. However, a method to solve the above problem has not yet been established.

[0011] The inventors of the present invention have been conducting research to provide a method for easily and stably decomposing thiocyanate ions in wastewater containing thiocyanate ions using the activated sludge method. In this research, the inventors conceived of supplying nutrients to the activated sludge as a means to easily stabilize thiocyanate decomposition in the activated sludge.

[0012] Generally, nitrogen and phosphorus are known components of microbial nutrients in activated sludge, and these are sometimes used in amounts that take into account the balance with the BOD (biochemical oxygen demand) of the wastewater flowing into the biological treatment tank containing the activated sludge. However, no nutrient component is known that promotes the decomposition of thiocyanate ions in coke oven wastewater.

[0013] The inventors of the present invention, through tests using activated sludge and various metal salts in coke oven wastewater treatment facilities, discovered that activated sludge requires copper ions to decompose thiocyanate ions. They then found that supplying copper ions as a nutrient for activated sludge improves the activated sludge's ability to decompose thiocyanate ions and stabilizes thiocyanate ion decomposition, leading to the present invention.

[0014] A wastewater treatment method according to an embodiment of the present invention (hereinafter may be referred to as "the present method") includes a biological treatment step in which wastewater containing thiocyanate ions is introduced into a biological treatment tank containing activated sludge to perform biological treatment. In the present method, as a nutrient for activated sludge, copper ions are supplied at a concentration of 0.01 to 2 mg-Cu / L in terms of copper equivalent concentration relative to the mixture of wastewater introduced into the biological treatment tank and the activated sludge, and the biological treatment step is performed.

[0015] A nutrient for activated sludge according to an embodiment of the present invention (hereinafter may be simply referred to as "the nutrient") is used in the above-mentioned present method, and contains a copper ion supply source that serves as a supply source of copper ions to activated sludge. That is, the nutrient is used in a wastewater treatment method including a biological treatment step in which wastewater containing thiocyanate ions is introduced into a biological treatment tank containing activated sludge to perform biological treatment. Furthermore, the nutrient contains a copper ion supply source as an active ingredient, and is used at a concentration of 0.01 to 2 mg-Cu / L in terms of copper equivalent concentration relative to the mixture of wastewater introduced into the biological treatment tank and the activated sludge.

[0016] In the present method, copper ions are supplied to activated sludge at a concentration of 0.01 to 2 mg-Cu / L in terms of copper equivalent concentration relative to the mixture of wastewater introduced into a biological treatment tank (also referred to as an aeration tank) and activated sludge. Therefore, the copper ion supply source used in this dosage functions as a nutrient for activated sludge. That is, the present method enables simple and stable decomposition treatment of thiocyanate ions in wastewater. In other words, when the biological treatment step is performed by supplying copper ions within the above concentration range, the decomposition rate of thiocyanate ions in wastewater is increased compared to when the biological treatment step is performed without supplying any copper ions, and it becomes possible to improve the decomposition rate of thiocyanate ions by activated sludge. When copper ions are supplied at a concentration less than 0.01 mg-Cu / L, copper ions hardly function as a nutrient, and the above effect is hardly obtained. On the other hand, when copper ions are supplied at a concentration exceeding 2 mg-Cu / L, copper ions cause biotoxicity to activated sludge, which reduces the decomposition ability of thiocyanate ions.

[0017] The wastewater to be treated by the present method is not particularly limited as long as it is wastewater containing a COD component including at least thiocyanate ions. Examples of such wastewater include coke oven wastewater generated during coal carbonization in a coke oven. Coke oven wastewater includes condensed water generated by cooling exhaust gas discharged when coke is produced from coal, and may be scrubber wastewater after treatment with a scrubber or the like.

[0018] Since coke oven wastewater is preferred as the wastewater, wastewater further containing ammonia, phenol which is a type of COD component, and the like in addition to thiocyanate ions is suitable. Further, the wastewater may be pretreated wastewater before flowing into a biological treatment tank. For example, when the wastewater further contains cyanide ions (CN - ) in addition to thiocyanate ions, the wastewater that has been subjected to treatment for reducing cyanide ions in the wastewater may be used as the water to be treated. Further, it is preferable that the wastewater does not contain copper ions, or the concentration of copper ions in the wastewater is less than 0.2 mg-Cu / L.

[0019] As the copper ions supplied to the activated sludge, at least one copper ion supply source can be used, which is selected from: a copper ion-containing solution containing copper ions generated from a copper compound by dissolving the copper compound in a solvent; and a solid copper compound that generates copper ions when added to wastewater. Among these, it is more preferable to use a copper ion-containing solution from the viewpoint of ease of use and easy supply of copper ions to activated sludge.

[0020] 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.

[0021] In this method, the copper ion supply source is preferably in the form of a solution, from the viewpoint of ease of use and ease of supply to activated sludge, and is preferably used as a nutrient (its active ingredient) in the form of a solution. Therefore, it is preferable that the nutrient further contains water and is in the form of a solution.

[0022] The copper ions can be supplied at a concentration of 0.01 to 2 mg-Cu / L in terms of copper equivalent in a mixture of wastewater and activated sludge. There are no particular restrictions on the location or target of the copper ion source addition. The copper ion source is used as a nutrient for activated sludge, and the decomposition of thiocyanate ions by the activated sludge is promoted by the copper ions. Therefore, the copper ion source can be added anywhere in the biological treatment process system so that copper ions are supplied to the activated sludge in the biological treatment tank.

[0023] One embodiment of the method, regarding the location and target of the addition of the copper ion source, is that the copper ion source can be added to wastewater containing thiocyanate ions. By adding the copper ion source to the wastewater, it becomes possible to introduce copper ions into the wastewater, and by flowing this wastewater into a biological treatment tank, copper ions can be supplied to the activated sludge in the biological treatment tank.

[0024] Furthermore, one embodiment of the method regarding the location and target of the addition of the copper ion source is that the copper ion source can be added to the biological treatment tank containing wastewater and activated sludge. By adding the copper ion source to the biological treatment tank, copper ions can be supplied to the activated sludge contained in the biological treatment tank. In addition, by adding the copper ion source to the biological treatment tank, the target of the copper ion source becomes a mixture containing wastewater and activated sludge in the biological treatment tank, making it easier to control the amount of copper ion source supplied in terms of the copper equivalent concentration mentioned above.

[0025] Furthermore, as one embodiment of the location and target of the addition of the copper ion source in this method, the copper ion source can also be added to the activated sludge, which will be used as the return sludge described later. By adding the copper ion source to the return sludge, the return sludge flows into the biological treatment tank, thereby supplying copper ions from the copper ion source to the activated sludge in the biological treatment tank.

[0026] The activated sludge used in the biological treatment process 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 thiocyanide-degrading bacteria.

[0027] The inventors analyzed the microbial flora of activated sludge collected from an aquatic water treatment facility equipped with a biological treatment tank containing activated sludge and found that microorganisms belonging to the order Chromatiales are highly likely to be responsible for decomposing thiocyanate ions. Therefore, it is even more preferable that the thiocyanate-degrading bacteria include bacteria belonging to the order Chromatiales. It is even more preferable that the bacteria belonging to the order Chromatiales include at least one bacterium selected from the group consisting of the genera Thiohalobacter, Halothiobacillus, Thioprofundum, Thiohalophilus, Allochromatium, and Thiogranum. Furthermore, based on the results of the above microbiome analysis, the activated sludge may further contain one or more species from the following: Nitrosococcus, Halochromatium, Thioalkalispira, Halorhodospira, Ectothiorhodospira, Granulosicoccus, Thioalbus, Thiohalocapsa, and Rheinheimera. Moreover, it is preferable that the activated sludge contains phenol-degrading bacteria.

[0028] Examples of biological treatment tanks containing activated sludge used in the biological treatment process 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); and 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. 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] The treatment time (reaction time) in the biological treatment process 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 biological treatment process 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.

[0030] In one embodiment of this method, a mixture of treated water obtained from the biological treatment process and activated sludge may be obtained from the wastewater after the biological treatment process. In one embodiment of this method, it is preferable to further include a solid-liquid separation step after the biological treatment process 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 the return sludge described above. This allows for a continuous activated sludge biological treatment process and makes it easier to maintain the concentration of MLSS (activated sludge suspended solids) in the biological treatment tank within a certain range. The concentration of MLSS in the biological treatment tank is preferably 500 to 10000 mg / L. It is also preferable to use the membrane-type activated sludge tank described above as the biological treatment tank and perform solid-liquid separation treatment within that tank.

[0031] 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 above-described biological treatment process may be a sedimentation-type activated sludge method in which a sedimentation tank is installed downstream of the biological treatment tank, or a membrane-type activated sludge method in which a separation membrane is installed downstream of the biological treatment tank. Furthermore, as described above, 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. Alternatively, the biological treatment may be carried out using the above-described membrane-type activated sludge tank in which a membrane separation device is installed in the tank as the biological treatment tank. Activated sludge and treated water can be separated from the above-described mixed liquid using solid-liquid separation equipment such as sedimentation tanks and filtration devices. The activated sludge obtained through solid-liquid separation can be returned to the biological treatment tank and reused as returned sludge.

[0032] As detailed above, the wastewater treatment method of one embodiment of the present invention includes a biological treatment step in which wastewater containing thiocyanate ions is introduced into a biological treatment tank containing activated sludge and subjected to biological treatment. Furthermore, by a simple method in which copper ions are supplied as a nutrient for the activated sludge at a concentration of 0.01 to 2 mg-Cu / L in terms of copper equivalent to the mixture of wastewater and activated sludge flowing into the biological treatment tank, it is possible to stably decompose thiocyanate ions in the wastewater.

[0033] Furthermore, one embodiment of the present invention can have the following configuration. [1] A wastewater treatment method comprising a biological treatment step of introducing wastewater containing thiocyanate ions into a biological treatment tank containing activated sludge for biological treatment, A method for treating wastewater, comprising supplying copper ions as a nutrient for the activated sludge at a concentration of 0.01 to 2 mg-Cu / L in terms of copper equivalent to the mixture of wastewater and activated sludge flowing into the biological treatment tank, and performing the biological treatment step. [2] The wastewater treatment method according to [1] above, using at least one copper ion source as the copper ions: a copper ion-containing solution containing the copper ions generated from the copper compound by dissolving the copper compound in a solvent; and a solid copper compound that generates copper ions when added to the wastewater. [3] The wastewater treatment method according to [2] above, comprising adding the copper ion supply source to the wastewater. [4] The wastewater treatment method according to [2] or [3] above, comprising adding the copper ion supply source to the biological treatment tank in which the wastewater and the activated sludge are present. [5] After the biological treatment step, the process further includes a solid-liquid separation step in which a mixture of treated water obtained in the biological treatment step and activated sludge is separated from the wastewater, A wastewater treatment method according to any one of [2] to [4] above, comprising adding the copper ion supply source to the returned sludge, which is separated from the treated water by the solid-liquid separation step and returned to the biological treatment tank. [6] The wastewater treatment method according to any of [1] to [5] above, wherein the wastewater is coke oven wastewater. [7] The activated sludge contains thiocyanide-degrading bacteria, The wastewater treatment method according to any one of the above [1] to [6], which includes the thiocyanide-degrading bacteria belonging to the order Chromatiales. [8] The wastewater treatment method according to [7] above, wherein the bacteria belonging to the order Chromatiales includes at least one bacterium selected from the group consisting of the genus Thiohalobacter, Halothiobacillus, Thioprofundum, Thiohalophilus, Allochromatium, and Thiogranum. [9] A nutrient for activated sludge used in any one of the wastewater treatment methods described in item [1] to [8] above, A nutrient for activated sludge containing a copper ion source that serves as a source of copper ions to the activated sludge.

[10] The activated sludge nutrient described in [9] above, further containing water and in the form of a solution. [Examples]

[0034] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0035] <Measurement method> (SCN - (Method of analyzing concentration) In the following test example, thiocyanate ion (SCN -The concentration was analyzed by a colorimetric method using iron nitrate. Specifically, a dilution series was prepared by diluting an aqueous solution of sodium thiocyanate (NaSCN) (10 g-SCN / L). To 2 mL of the sample from this dilution series, 160 μL of 2.5 N nitric acid and 80 μL each of aqueous iron(II) nitrate were added. The absorbance was measured at a wavelength of 460 nm immediately after color development. As a result, a linear calibration curve was obtained in the range of 0 to 30 mg-SCN / L. In the test examples described below, the measurement samples were diluted so that the thiocyanate ion concentration was in the range of 0 to 30 mg-SCN / L, and the colorimetric test was performed using the method described above. From the obtained absorbance values, the thiocyanate ion concentration (mg-SCN / L) was calculated from the calibration curve.

[0036] <Preliminary Examination Example Series 1> For each of the preliminary test examples 1-1 to 1-7, a simulated wastewater 1 was prepared to resemble coke oven wastewater. Specifically, 100 mL of simulated wastewater 1 was prepared for each preliminary test example 1 by mixing and dissolving the components shown in the left column of the upper section of Table 1 at the concentrations shown in the right column into 100 mL of a mixture of 60 mL of seawater and 40 mL of tap water shown in the lower section of Table 1. Simulated wastewater 1 was used as a culture medium for activated sludge. This will be referred to as simulated wastewater culture medium 1.

[0037] TIFF0007927650000001.tif55170

[0038] 50 µL of activated sludge was added to 2.5 mL of simulated wastewater medium 1 placed in a culture test tube (hereinafter simply referred to as "test tube") (final MLSS concentration = 50 mg / L). Thus, a mixture of simulated wastewater and activated sludge was placed into the test tube. Further, a metal salt shown in the top row of Table 2 was added to the test tube such that the concentration in terms of metal element relative to the mixture of simulated wastewater and activated sludge reached the value shown in the "Added metal salt concentration (mg-metal / L)" column of Table 2, followed by aerobic shaking culture at 30°C. Six types of metal salts were used: zinc sulfate (ZnSO4), cobalt(II) sulfate (CoSO4), sodium molybdate (Na2MoO4), manganese(II) chloride (MnCl2), sodium selenite (Na2SeO3), and copper(II) sulfate (CuSO4). In Preliminary Test Examples 1-1 to 1-6, one of the six metal salts was set as the condition of absence, and in Preliminary Test Example 1-7, all six metal salts were set as the condition of presence.

[0039] After 5 days of culture (after 120 hours), thiocyanate ion (SCN - ) concentration (mg-SCN / L) in the liquid (culture solution) in the test tube was measured, and the thiocyanate ion decomposition ratio (%) was determined by the following formula. The results are shown in the "SCN - decomposition ratio (%)" column of Table 2. Thiocyanate ion decomposition ratio (%) =(1-(SCN on day 5 - concentration / SCN on day 0 - concentration))×100

[0040] TIFF0007927650000002.tif60170

[0041] Preliminary Test Example 1-6 resulted in a significantly lower thiocyanate ion decomposition ratio compared to Preliminary Test Examples 1-1 to 1-5 and 1-7. From these results, it was found that decomposition of thiocyanate ion was significantly suppressed in the absence of copper ion (Cu 2+ ) from the copper ion supply source (CuSO4). From this, it was considered that copper ions are effective for improving the thiocyanate ion decomposition ability by activated sludge.

[0042] <Test Example A Series> As part of the Test Example A series, Examples A1 to A4 and Comparative Examples A1 to A3, described below, were carried out. In each of these Test Example A series, a mixture of simulated wastewater 2, prepared to resemble coke oven wastewater, and activated sludge was used as the wastewater. Specifically, simulated wastewater 2 was prepared by mixing and dissolving the components shown in the left column of the upper section of Table 3 at the concentrations shown in the right column into 593 mL of a mixture of 186 mL of seawater and 407 mL of tap water, as shown in the lower section of Table 3. Simulated wastewater 2 was used as the culture medium for activated sludge. This will be referred to as simulated wastewater culture medium 2. To this 593 mL of simulated wastewater culture medium 2, 107 mL of activated sludge (MLSS concentration = 13245 mg / L) collected from an ammonia treatment facility was mixed (MLSS concentration of the mixture = 2000 mg / L). A mixture of this simulated wastewater culture medium 2 and activated sludge was dispensed in 100 mL portions into shaking Erlenmeyer flasks (hereinafter simply referred to as "flasks") for each of Test Example A (Examples A1-A4 and Comparative Examples A1-A3).

[0043] TIFF0007927650000003.tif47170

[0044] To a mixture of simulated wastewater medium 2 and activated sludge placed in a flask, a 1 mg-Cu / L concentration of cupric chloride (CuCl2) aqueous solution was added as a copper ion source, such that the copper equivalent concentration relative to the mixture was as shown in the "Copper Ion Supply (mg-Cu / L)" column of Table 4. The pH of the mixture of simulated wastewater medium 2 and activated sludge in all of Test Example A was 8.0. The biological treatment process was carried out for 42 hours by aerobic shaking culture at 30°C. Every hour from the start of the biological treatment process, 1 mL was sampled from the supernatant in the flask and thiocyanate ions (SCN) were tested. - The concentration (mg-SCN / L) was measured. In all Test Example A, the SCN at the time when the decomposition of thiocyanate ions began (after 25-27 hours) was measured. - From the concentration, the following formula gives SCN - The degradation rate (mg / L / Hr) was calculated. Furthermore, the SCN after 27 hours from the start of the test was calculated using the following formula. -The decomposition ratio (%) was calculated. The results are shown in Table 4. SCN - Decomposition rate (mg / L / Hr) =(SCN after 25 hours) - Concentration - SCN at 27 hours - concentration) / 2 hours SCN after 27 hours - Decomposition rate (%) =(1-(SCN after 27 hours) - Concentration / SCN at the start of the test - Concentration))×100

[0045] TIFF0007927650000004.tif62170

[0046] From Test Example A, in the biological treatment process, when the amount of copper ions supplied to the mixture of wastewater and activated sludge is 0.01 to 2.0 mg-Cu / L in terms of copper equivalent concentration (Examples A1 to A4), the SCN is higher compared to when no copper ions are supplied (Comparative Example A1). - It was confirmed that the decomposition rate and decomposition rate were high. Furthermore, when the amount of copper ions supplied to the mixture of wastewater and activated sludge was less than 0.01 mg-Cu / L in terms of copper equivalent concentration (Comparative Example A2), the effect obtained in the examples was not observed. Moreover, when the amount of copper ions supplied to the mixture of wastewater and activated sludge was greater than 2 mg-Cu / L in terms of copper equivalent concentration (Comparative Example A3), SCN - The decomposition rate and decomposition rate were lower than in Comparative Example A1. This was thought to be due to the biotoxicity of copper ions to activated sludge. Based on the results of Test Example A above, it is possible to improve the decomposition rate and decomposition rate of thiocyanate ions by supplying a predetermined amount of copper ions, making it possible to decompose thiocyanate ions simply and stably.

[0047] Microbial flora analysis of activated sludge collected from the ammonia treatment facility used in Test Example A revealed that it contains bacteria belonging to the order Chromatiales, which are thought to be thiocyan-degrading bacteria, including the genera Thiohalobacter, Halothiobacillus, Thioprofundum, Thiohalophilus, Allochromatium, and Thiogranum. Furthermore, the activated sludge was found to contain bacteria belonging to the order Chromatiales, including the genera Nitrosococcus, Halochromatium, Thioalkalispira, Halorhodospira, Ectothiorhodospira, Granulosicoccus, Thioalbus, Thiohalocapsa, and Rheinheimera.

[0048] The microbial community analysis of the activated sludge described above was performed using the following method. DNA was extracted from the activated sludge, and the V4-V5 region of the 16S rRNA gene was PCR amplified using primers shown in Table 5, which contain the sequences necessary for sequencing analysis. Sequencing analysis was then performed using a next-generation sequencer (product name "MiSeq," Illumina). Approximately 250 base pairs were analyzed from both sides of the PCR amplification product (paired-end sequencing). For the obtained sequences, a homology search was performed against the greengenes 16S rRNA gene database to estimate the phylogenetic classification.

[0049] TIFF0007927650000005.tif35170

Claims

1. A wastewater treatment method comprising a biological treatment step in which wastewater containing thiocyanate ions is introduced into a biological treatment tank containing activated sludge with thiocyanide-degrading bacteria for biological treatment, A method for treating wastewater, comprising using a nutrient for activated sludge that promotes the decomposition of thiocyanate ions and contains a copper ion source, and supplying copper ions to the activated sludge at a concentration of 0.01 to 2 mg-Cu / L as a copper equivalent concentration in the mixture of wastewater and activated sludge flowing into the biological treatment tank, thereby performing the biological treatment step.

2. The wastewater treatment method according to Claim 1, wherein the copper ion supply source is at least one of: a copper ion-containing solution containing copper ions generated from a copper compound by dissolving the copper compound in a solvent; and a solid copper compound that generates copper ions when added to the wastewater.

3. The wastewater treatment method according to claim 2, comprising adding the activated sludge nutrient containing the copper ion supply source to the wastewater.

4. The wastewater treatment method according to claim 2, comprising adding the activated sludge nutrient containing the copper ion supply source to the biological treatment tank in which the wastewater and the activated sludge are present.

5. The process further includes a solid-liquid separation step in which, after the biological treatment step, a mixture of treated water obtained from the biological treatment step and activated sludge is separated from the wastewater into solid and liquid components. The wastewater treatment method according to claim 2, further comprising adding the activated sludge containing the copper ion supply source to the returned sludge, which is separated from the treated water by the solid-liquid separation step and returned to the biological treatment tank.

6. The wastewater treatment method according to claim 1, wherein the wastewater is coke oven wastewater.

7. The wastewater treatment method according to claim 1, wherein the thiocyanide-degrading bacteria include bacteria belonging to the order Chromatiales.

8. The wastewater treatment method according to claim 7, wherein the bacteria belonging to the order Chromatiales include at least one bacterium selected from the group consisting of the genus Thiohalobacter, Halothiobacillus, Thioprofundum, Thiohalophilus, Allochromium, and Thiogranum.

9. A nutrient for activated sludge used in the wastewater treatment method described in any one of claims 1 to 8, A nutrient for activated sludge that promotes the decomposition of thiocyanate ions, containing the copper ion source which serves as a source of copper ions to the activated sludge.

10. Furthermore, the activated sludge nutrient according to claim 9 contains water and is in the form of a solution.

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