Method and apparatus for removing color from organic wastewater

Abstract

To provide a method of removing chromaticity of organic wastewater by adding an aluminum-based coagulant with an optimal adding amount.SOLUTION: A chromaticity removal method includes: subjecting organic wastewater to biological treatment in a biological treatment tank 1 and removing an organic matter from the organic wastewater to produce biologically-treated water; filtering the biologically-treated water with a first filter 5; measuring chromaticity of the biologically-treated water filtered by the first filter 5 with a first color meter 6; determining an adding amount of an aluminum-based coagulant based on the chromaticity measured by the first color meter 6; adding the determined adding amount of the aluminum-based coagulant to the biologically-treated water to produce chromaticity-treated water; filtering the chromaticity-treated water with a second filter 12; measuring chromaticity of the chromaticity-treated water filtered by the second filter 12 with a second color meter 15; and adjusting an adding amount of the aluminum-based coagulant based on the chromaticity measured by the second color meter 15.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for removing the chromaticity of organic wastewater such as food wastewater, beverage wastewater, urine, and septic tank sludge.

Background Art

[0002] In recent years, from the viewpoints of water environment conservation and safety of rivers and the like, the requirements for the chromaticity of effluent water have been increasing. For example, organic wastewater such as food wastewater, beverage wastewater, urine, and septic tank sludge often contains chromaticity components, so it is required to remove chromaticity during discharge. However, the wastewater generated in food manufacturing factories, beverage manufacturing factories, etc. has large fluctuations in water volume and quality in a short time depending on the production items and production processes, so stable chromaticity treatment is difficult.

[0003] In the chromaticity removal treatment, a method is often used in which a flocculant is added to the organic wastewater to flocculate and remove organic substances and colloidal substances, which are chromaticity components in the organic wastewater. The addition amount of the flocculant is often determined from the results of a flocculation test by a jar test. However, since it takes time to obtain the results by the jar test, the addition rate of the flocculant cannot be reflected in real time.

[0004] FIG. 4 is a schematic diagram showing an example of a conventional chromaticity treatment apparatus. The organic wastewater is first biologically treated in a biological treatment tank 501. Thereafter, the organic wastewater is sent to a chromaticity treatment tank 502, where a flocculant is added to the organic wastewater from a flocculant addition device 503, and chromaticity treatment is performed. The chromaticity-treated organic wastewater is sent to a flocculation sedimentation tank 504 and separated into flocculant sludge and flocculation-treated water. The flocculation-treated water is discharged as effluent water. The flocculant sludge is sent to a sludge treatment device 505, where water is further separated from the flocculant sludge. The separated water is returned to the biological treatment tank 501 and treated again.

[0005] Conventional technology employs feedback control, as shown in Figure 4, which involves measuring the chromaticity of the effluent using a colorimetric method or spectrophotometer and then adjusting the amount of coagulant added. However, this control method is insufficient for chromaticity removal, and the chromaticity of the effluent may exceed the management standard. Therefore, in order to prevent the chromaticity of the effluent from exceeding the management standard, it is necessary to operate with an excessive amount of coagulant added to cope with sudden increases in high-chromaticity wastewater, which leads to increased coagulant costs and sludge generation, contributing to high treatment costs.

[0006] In coagulation and sedimentation treatment targeting chromatic components, as shown in Figure 4, aluminum-based coagulants such as polyaluminum chloride (PAC), aluminum chloride, and aluminum sulfate are used as coagulants. In beverage factories, wastewater containing chromatic components is discharged intermittently, so it was necessary to operate with a large amount of aluminum-based coagulant added at all times to respond without delay when high-chromatic wastewater occurred. However, the following problems arose due to the excessive addition of aluminum-based coagulants.

[0007] As shown in Figure 4, the water separated from the concentrated sludge in the sludge treatment device 505 is returned to the biological treatment tank 501 for retreatment. However, due to an excess of aluminum-based coagulant, excess aluminum remains in the separated water, causing the aluminum concentration in the biological treatment tank 501 to rise to several tens of mg / L. This can lead to the accumulation of aluminum hydroxide as a gel in the activated sludge in the biological treatment tank 501, potentially hindering the biological treatment process.

[0008] Furthermore, excessive aluminum residue leads to the proliferation of filamentous organisms in the activated sludge, resulting in frequent filamentous bulking and a significant deterioration of solid-liquid separation performance in the subsequent coagulation and sedimentation tank. Furthermore, phosphates and other substances in the wastewater from the biological treatment tank 501 coagulate due to excess aluminum, leading to a deficiency of nutrients in the biological treatment and a deterioration of the treated water quality. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 4-193311 [Patent Document 2] Japanese Patent Publication No. 2018-161632 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Patent Document 1 describes measuring wastewater with a colorimeter, calculating and adding a coagulant based on the color and volume of the wastewater to perform decolorization treatment, and further measuring the organic concentration at the wastewater outlet to correct the amount of coagulant added. However, since the wastewater to be treated has high turbidity, it is difficult to apply a colorimeter.

[0011] Patent Document 2 describes a method of filtering treated water using a filter, measuring the ultraviolet absorbance (measurement wavelength 200-400 nm) and visible light absorbance (measurement wavelength 400-800 nm) of the filtrate, calculating the organic concentration from the difference between these measurements, and controlling the amount of coagulant added. However, because this is a feedback control method that measures the chromaticity of the treated water after chromaticity removal and controls the amount of coagulant added, it is difficult to address high-chromatic wastewater and control over-injection. Furthermore, since it measures organic concentration rather than chromaticity, it is not possible to confirm whether the chromaticity of the treated water meets the management standard value.

[0012] When incorporating biological treatment into wastewater treatment, residual aluminum has a significant impact, making it crucial to optimize the amount of aluminum-based coagulant added to achieve both color removal and stable wastewater treatment simultaneously.

[0013] Therefore, the present invention provides a method and apparatus for removing the color of organic wastewater by adding an aluminum-based coagulant in an optimal amount. [Means for solving the problem]

[0014] In one embodiment, a method for removing the color of organic wastewater is provided, which involves biologically treating organic wastewater in a biological treatment tank to produce biologically treated water from which organic matter has been removed, filtering the biologically treated water in a first filter, measuring the color of the biologically treated water filtered in the first filter with a first colorimeter, determining the amount of aluminum-based coagulant to be added based on the color measured by the first colorimeter, adding the determined amount of aluminum-based coagulant to the biologically treated water to produce color-treated water, filtering the color-treated water in a second filter, measuring the color of the color-treated water filtered in the second filter with a second colorimeter, and adjusting the amount of aluminum-based coagulant to be added based on the color measured by the second colorimeter.

[0015] In one embodiment, the color removal method further includes the step of adding the adjusted amount of the aluminum-based coagulant to the subsequent biologically treated water produced in the biological treatment tank, thereby reducing the color of the subsequent biologically treated water to 100 degrees or less. In one embodiment, the first colorimeter measures the absorbance at a first wavelength, and the second colorimeter measures the absorbance at a second wavelength that is shorter than the first wavelength. In one embodiment, the color removal method further includes, before filtering the biologically treated water with the first filter, introducing the biologically treated water generated in the biological treatment tank into a solid-liquid separation tank to separate sludge from the biologically treated water, and returning the separated sludge to the biological treatment tank. In one embodiment, the color removal method further includes the steps of adding a polymer flocculant to the color-treated water to produce flocculated water and flocculated sediment sludge, separating water from the flocculated sediment sludge, and returning the separated water to the biological treatment tank.

[0016] In one embodiment, a method for removing the color of organic wastewater is provided, which involves performing a membrane separation activated sludge method on organic wastewater using a membrane separation tank to remove organic matter and turbidity from the organic wastewater, measuring the color of the biologically treated water with a first colorimeter, determining the amount of aluminum-based coagulant to be added based on the color measured by the first colorimeter, adding the determined amount of aluminum-based coagulant to the biologically treated water to produce color-treated water, filtering the color-treated water with a filter, measuring the color of the filtered color-treated water with a second colorimeter, and adjusting the amount of aluminum-based coagulant to be added based on the color measured by the second colorimeter.

[0017] In one embodiment, the color removal method further includes the step of adding the adjusted amount of the aluminum-based coagulant to the subsequent biologically treated water produced in the membrane separation tank, thereby reducing the color of the subsequent biologically treated water to 100 degrees or less. In one embodiment, the first colorimeter measures the absorbance at a first wavelength, and the second colorimeter measures the absorbance at a second wavelength that is shorter than the first wavelength. In one embodiment, the color removal method further includes the steps of adding a polymer flocculant to the color-treated water to produce flocculated water and flocculated sediment sludge, separating water from the flocculated sediment sludge, and returning the separated water to the membrane separation tank.

[0018] In one embodiment, an organic wastewater color removal device is provided, comprising: a biological treatment tank that biologically treats organic wastewater to produce biologically treated water from which organic matter has been removed by biological treatment of the organic wastewater; a first filter for filtering the biologically treated water; a first colorimeter for measuring the color of the biologically treated water filtered by the first filter; a control device for determining the amount of aluminum-based coagulant to be added based on the color measured by the first colorimeter; an aluminum-based coagulant adding device for adding the determined amount of aluminum-based coagulant to the biologically treated water; a color treatment tank that stirs the biologically treated water and the aluminum-based coagulant to produce color-treated water; a second filter for filtering the color-treated water; and a second colorimeter for measuring the color of the color-treated water filtered by the second filter, wherein the control device is configured to adjust the amount of aluminum-based coagulant to be added based on the color measured by the second colorimeter.

[0019] In one embodiment, the first colorimeter is configured to measure absorbance at a first wavelength, and the second colorimeter is configured to measure absorbance at a second wavelength shorter than the first wavelength. In one embodiment, the color removal device further comprises a solid-liquid separation tank positioned between the biological treatment tank and the first filter, which separates sludge from the biologically treated water before it is filtered by the first filter, and a sludge return line that returns the separated sludge to the biological treatment tank. In one embodiment, the color removal apparatus further comprises a polymer flocculant adding device for adding a polymer flocculant to the color-treated water, a flocculation and sedimentation tank for stirring the color-treated water and the polymer flocculant to produce flocculated water and flocculated sedimented sludge, a sludge treatment device for separating water from the flocculated sedimented sludge, and a separated water return line for returning the separated water to the biological treatment tank.

[0020] In one aspect, there is provided a color removal device for organic wastewater, comprising a membrane separation tank that performs a membrane separation activated sludge method on the organic wastewater to generate biologically treated water from which organic substances and turbidity have been removed; a first colorimeter that measures the colority of the biologically treated water; a control device that determines the addition amount of an aluminum-based flocculant based on the colority measured by the first colorimeter; an aluminum-based flocculant addition device that adds the determined addition amount of the aluminum-based flocculant to the biologically treated water; a color treatment tank that stirs the biologically treated water and the aluminum-based flocculant to generate color-treated water; a filter that filters the color-treated water; and a second colorimeter that measures the colority of the color-treated water filtered by the filter. The control device is configured to adjust the addition amount of the aluminum-based flocculant based on the colority measured by the second colorimeter.

[0021] In one aspect, the first colorimeter is configured to measure the absorbance at a first wavelength, and the second colorimeter is configured to measure the absorbance at a second wavelength shorter than the first wavelength. In one aspect, the color removal device further comprises a polymer flocculant addition device that adds a polymer flocculant to the color-treated water; a coagulation sedimentation tank that stirs the color-treated water and the polymer flocculant to generate coagulated treated water and coagulated sediment sludge; a sludge treatment device that separates water from the coagulated sediment sludge; and a separated water return line that returns the separated water to the membrane separation tank.

Advantages of the Invention

[0022] According to the method and device for removing the chromaticity of organic wastewater according to the present invention, the dosage of the flocculant is determined based on the chromaticity of the biologically treated water obtained by biologically treating the organic wastewater, and further, the dosage of the flocculant is adjusted based on the chromaticity of the chromaticity-treated water. Therefore, the chromaticity can be removed from the organic wastewater with an optimal flocculant. In particular, before being measured by the first chromaticity meter, the first filter or the membrane separation tank filters the biologically treated water, so the first chromaticity meter can accurately measure the chromaticity of the biologically treated water from which turbidity has been removed. Similarly, before being measured by the second chromaticity meter, the second filter filters the chromaticity-treated water, so the second chromaticity meter can accurately measure the chromaticity of the chromaticity-treated water from which turbidity has been removed. As a result, the optimal dosage of the aluminum-based flocculant can be determined.

Brief Description of the Drawings

[0023] [Figure 1] It is a schematic diagram showing an embodiment of a device for removing the chromaticity of organic wastewater. [Figure 2] It is a schematic diagram showing another embodiment of a device for removing the chromaticity of organic wastewater. [Figure 3] It is a table showing the implementation results of the chromaticity removal treatment [Figure 4] It is a schematic diagram showing an example of a conventional chromaticity removal device.

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram showing one embodiment of a color removal device for organic wastewater. The color removal device comprises a biological treatment tank 1 that biologically treats organic wastewater to produce biologically treated water from which organic matter has been removed, a first filter 5 that filters the biologically treated water, a first colorimeter 6 that measures the color of the biologically treated water filtered by the first filter 5, a control device 7 that determines the amount of aluminum-based coagulant to be added based on the color measured by the first colorimeter 6, an aluminum-based coagulant adding device 8 that adds the determined amount of aluminum-based coagulant to the biologically treated water, a color treatment tank 10 that stirs the biologically treated water and the aluminum-based coagulant to produce color-treated water, a second filter 12 that filters the color-treated water, and a second colorimeter 15 that measures the color of the color-treated water filtered by the second filter 12. The control device 7 is configured to control the operation of the aluminum-based flocculant additive device 8, and is configured to determine the amount of aluminum-based flocculant to be added based on the chromaticity measured by the first colorimeter 6, and further adjust the amount of aluminum-based flocculant to be added based on the chromaticity measured by the second colorimeter 15.

[0025] The organic wastewater to be treated is not particularly limited as long as it contains organic matter. Specific examples of organic wastewater include wastewater obtained from food or beverage manufacturing plants, dyeing wastewater, or wastewater containing organic waste, sludge, human waste, septic tank sludge, food waste, etc. A high chromaticity removal effect can be obtained when food or beverage manufacturing wastewater generated in the food or beverage manufacturing process is used as the organic wastewater according to this embodiment. The chromaticity of the organic wastewater to be treated is typically 100 to 1000 degrees, more typically 200 to 1000 degrees, and even more typically 200 to 500 degrees.

[0026] The biological treatment tank 1 is a reaction tank for carrying out activated sludge methods, biofilm methods, anaerobic treatment methods, biological nitrification-denitrification methods, multi-stage activated sludge methods, fluidized carrier methods, etc., and may be equipped with aeration equipment, etc., as needed. Biological treatment using microorganisms is carried out in the biological treatment tank 1. In one embodiment, the biological treatment tank 1 is an activated sludge tank containing activated sludge inside.

[0027] In this embodiment, as shown in Figure 1, the color removal device further includes a solid-liquid separation tank 2 for separating sludge from the biologically treated water before it is filtered by the first filter 5, and a sludge return line 11 for returning the separated sludge to the biological treatment tank 1. The solid-liquid separation tank 2 is located between the biological treatment tank 1 and the first filter 5. The solid-liquid separation tank 2 is used to separate the sludge generated by biological treatment from the biologically treated water obtained in the biological treatment tank 1.

[0028] The chromaticity treatment tank 10 is configured to produce chromaticity-treated water with reduced or removed chromaticity by stirring the biologically treated water, which is generated in the biological treatment tank 1 and subjected to solid-liquid separation treatment in the solid-liquid separation tank 2, with an aluminum-based coagulant using a stirrer. The aluminum-based coagulant addition device 8 is connected to the chromaticity treatment tank 10. Biologically treated water from which sludge has been separated in the solid-liquid separation tank 2 is introduced into the chromaticity treatment tank 10, and the biologically treated water and the aluminum-based coagulant are mixed and stirred, thereby removing organic substances and colloidal substances that have chromatic components, and reducing or removing the chromaticity. The aluminum-based coagulant can be any of PAC (polyaluminum chloride), aluminum chloride, or aluminum sulfate, and a high chromaticity removal effect can be obtained when PAC or aluminum chloride is used.

[0029] The first filter 5 is connected to the piping between the solid-liquid separation tank 2 and the chromaticity treatment tank 10, or to the inlet of the chromaticity treatment tank 10. As the first filter 5, sand filtration, membrane filtration, or a filter using filter media made of fibers or polymer materials can be used. In particular, the use of membrane filtration is desirable because it can obtain the clarity of the filtered water necessary for chromaticity measurement. The pore size of the first filter 5 is 0.4 to 5 μm, preferably 0.4 to 2 μm, and more preferably 0.4 to 1 μm.

[0030] A first colorimeter 6 is connected to the first filter 5 for measuring the color of the biologically treated water filtered by the first filter 5. The first colorimeter 6 is configured to measure the absorbance of the biologically treated water at a first wavelength. More specifically, the first colorimeter 6 measures the absorbance at a wavelength in the range of 250 to 500 nm, preferably in the range of 400 to 500 nm, and particularly preferably at a wavelength of 470 nm.

[0031] The second filter 12 is connected to the outlet of the chromaticity treatment tank 10. Similar to the first filter 5, the second filter 12 can utilize sand filtration, membrane filtration, or a filter media made of fiber or polymer material. In particular, the use of membrane filtration is desirable because it can obtain the clarity of the filtered water necessary for chromaticity measurement. The pore size of the second filter 12 is smaller than that of the first filter 5, and is 0.02 to 5 μm, preferably 0.02 to 2 μm, and more preferably 0.02 to 1 μm.

[0032] A second colorimeter 15 is connected to the second filter 12 for measuring the chromaticity of the chromaticity treated water filtered by the second filter 12. The second colorimeter 15 is configured to measure the absorbance of the chromaticity treated water at a second wavelength that is shorter than the first wavelength used by the first colorimeter 6. The second colorimeter 15 measures the absorbance at a wavelength in the range of 250 to 500 nm, preferably in the range of 250 to 400 nm, and particularly preferably at a wavelength of 390 nm. Because the second colorimeter 15 is configured to measure the absorbance at a shorter wavelength, it is possible to measure the chromaticity of the chromaticity treated water with high accuracy even at low chromaticity levels.

[0033] The control device 7 is connected to the first colorimeter 6, the aluminum-based coagulant additive device 8, and the second colorimeter 15, and is configured to determine the addition rate of the aluminum-based coagulant based on the chromaticity measured by the first colorimeter 6 and the second colorimeter 15. For example, the control device 7 calculates the required removal chromaticity, which is expressed as the difference between the chromaticity of the biologically treated water measured by the first colorimeter 6 and the management standard value of the effluent, and calculates the amount of aluminum-based coagulant to be added so that the residual aluminum concentration does not exceed 1 mg / L. In addition, if the chromaticity of the treated water measured by the second colorimeter 15 exceeds the set management standard value, the control device 7 adjusts the amount of aluminum-based coagulant to be added, so that the aluminum-based coagulant additive device 8 can supply the necessary amount of aluminum-based coagulant to keep the effluent below the management standard value.

[0034] The control device 7 consists of at least one computer. The control device 7 includes a storage device 7a that stores a program for determining the optimal amount of aluminum-based flocculant to be added, and a processing device 7b that performs calculations according to the instructions contained in the program. The storage device 7a includes a main memory such as random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) or solid-state drive (SSD). Examples of processing devices 7b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the control device 7 is not limited to these examples.

[0035] The control device 7 stores a first calculation formula for determining the amount of aluminum-based flocculant to be added in its memory device 7a. The control device 7 inputs the chromaticity measured by the first chromatometer 6 into the first calculation formula and performs calculations according to the first calculation formula to determine (calculate) the amount of aluminum-based flocculant to be added.

[0036] The first calculation formula is expressed as follows: Amount of aluminum-based flocculant added (mg / L) = A × a + b However, A is the chromaticity measured by the first chromatometer 6, and a and b are constants. The constants a and b are predetermined from experiments or actual operation. More specifically, they are the values ​​such that the chromaticity of the chromatic treated water obtained in the chromaticity treatment tank 10 is 100 degrees or less, and the residual aluminum concentration in the chromatic treated water is 1 mg / L or less.

[0037] The control device 7 issues a command to the aluminum-based flocculant additive device 8 to add the amount of aluminum-based flocculant determined by the first calculation formula to the chromaticity treatment tank 10. Since the aluminum-based flocculant additive device 8 can supply only the necessary amount of aluminum-based flocculant, the chromaticity removal device can perform stable chromaticity removal treatment while reducing the amount of aluminum-based flocculant used.

[0038] If the chromaticity of the organic wastewater flowing into the biological treatment tank 1 is unexpectedly high, the chromaticity of the treated water obtained in the chromaticity treatment tank 10 may exceed 100 degrees. In such cases, the control device 7 adjusts (i.e., corrects) the amount of additive obtained in the first calculation formula using the following second calculation formula. Correction amount (mg / L) = (B - reference value) × c + d However, B is the chromaticity measured by the second chromatometer 15, and c and d are constants. The control standard value is, for example, 100. The above second calculation formula is stored in the memory device 7a of the control device 7. The control device 7 adjusts the amount of aluminum-based flocculant added by adding the correction amount obtained by the second calculation formula to the amount added by the first calculation formula.

[0039] The constants c and d are predetermined from experiments or actual operation. More specifically, they are the values ​​such that when an adjusted amount of aluminum-based coagulant, obtained by adding a correction amount obtained from the second calculation formula to the amount obtained from the first calculation formula, is added to the biologically treated water, the chromaticity of the chromatic treated water obtained in the chromatic treatment tank 10 is 100 degrees or less, and the residual aluminum concentration in the chromatic treated water is 1 mg / L or less.

[0040] As shown in Figure 1, the chromaticity removal apparatus of this embodiment further includes a polymer flocculant adding device 17 for adding a polymer flocculant to the chromaticity treated water obtained in the chromaticity treatment tank 10, a flocculation and sedimentation tank 19 for stirring the chromaticity treated water and polymer flocculant to produce flocculated water and flocculated sedimented sludge, a sludge treatment device 21 for separating water from the flocculated sedimented sludge, and a separated water return line 22 for returning the water separated in the sludge treatment device 21 to the biological treatment tank 1. The second filter 12 may be connected to the piping between the chromaticity treatment tank 10 and the flocculation and sedimentation tank 19, or to the inlet of the flocculation and sedimentation tank 19.

[0041] The polymer flocculant addition device 17 is connected to the coagulation and sedimentation tank 19, and by adding the polymer flocculant to the color-treated water in the coagulation and sedimentation tank 19, coagulated flocs are formed. The coagulated flocs settle in the coagulation and sedimentation tank 19, forming coagulated and sedimented sludge. Therefore, in the coagulation and sedimentation tank 19, the color-treated water is separated into coagulated water and coagulated and sedimented sludge. Examples of polymer flocculants used include cationic polymer flocculants, anionic polymer flocculants, and nonionic polymer flocculants. In addition to the polymer flocculant, floc-forming aids, alkaline agents (e.g., slaked lime, sodium hydroxide, soda ash, etc.), and / or coagulation aids may be added to the color-treated water, thereby more reliably removing suspended solids (SS) derived from biological treatment, including microorganisms.

[0042] The coagulated and settled sludge obtained in the coagulation and settling tank 19 is transferred to the sludge treatment device 21, where the coagulated and settled sludge is dewatered. The sludge treatment device 21 can be equipped with a sludge dewaterer, a concentration device, etc. The separated water obtained in the sludge treatment device 21 is returned to the biological treatment tank 1 via the separated water return line 22 for retreatment of the chromatic components. Since chromatic components may re-leach from the sludge into the separated water, and because the separated water contains a large amount of suspended solids (SS) components, the separated water is returned to the biological treatment tank 1 for retreatment.

[0043] The following describes one embodiment of a method for removing chromaticity from organic wastewater using the above-described chromaticity removal device.

[0044] <Biological treatment> Organic wastewater is first introduced into biological treatment tank 1, where it undergoes biological treatment using microorganisms. In biological treatment tank 1, substances that microorganisms can prey on, basically BOD (biochemical oxygen demand), are removed from the organic wastewater, and COD (chemical oxygen demand) and chromatic components are removed as part of the BOD. By performing biological treatment on organic wastewater, the biologically decomposable BOD contained in the organic wastewater can be reliably removed, thereby also removing COD and chromatic components. By performing this biological treatment as a pretreatment for chromatic removal, the amount of aluminum-based coagulant added in the chromatic removal treatment described later can be reduced, making it possible to remove chromatic components more efficiently. Examples of biological treatments that can be used include the activated sludge method, biofilm method, anaerobic treatment method, biological nitrification-denitrification method, multi-stage activated sludge method, and fluidized carrier method.

[0045] <Solid-liquid separation> In the solid-liquid separation tank 2, the sludge generated by the biological treatment is separated from the biologically treated water obtained in the biological treatment tank 1. <1st chromaticity measurement> The biologically treated water is transferred to the chromaticity treatment tank 10. In this embodiment, a solid-liquid separation tank 2 is located between the biological treatment tank 1 and the chromaticity treatment tank 10, so the biologically treated water from which sludge has been separated in the solid-liquid separation tank 2 is transferred to the chromaticity treatment tank 10. At this time, a portion of the biologically treated water is transferred to the first filter 5, where turbidity such as suspended solids (SS) is removed from the biologically treated water. The biologically treated water filtered in the first filter 5 is introduced into the first colorimeter 6, and the absorbance of the biologically treated water at the first wavelength is measured by the first colorimeter 6. The absorbance of the biologically treated water at the first wavelength represents the chromaticity of the biologically treated water.

[0046] <Chromaticity removal> In the chromaticity treatment tank 10, an aluminum-based coagulant is added to the biologically treated water, and the aluminum-based coagulant and the biologically treated water are mixed using a stirrer (not shown). This removes organic substances and colloidal substances that have chromatic components from the biologically treated water, resulting in chromatically treated water from which the chromaticity has been removed. In one embodiment, a pH adjusting agent is added to the biologically treated water in the chromaticity treatment tank 10, and the chromaticity removal treatment is performed at a pH of 5.0 to 8.0, preferably 6.5 to 7.5, and particularly preferably 7.0.

[0047] <Second chromaticity measurement> A portion of the chromaticity-removed water obtained from the chromaticity removal treatment is transferred to a second filter 12, where turbidity such as suspended solids (SS) is removed from the chromaticity-removed water. The chromaticity-removed water filtered in the second filter 12 is introduced into a second colorimeter 15, where the absorbance of the chromaticity-removed water at a second wavelength shorter than the first wavelength is measured by the second colorimeter 15. The absorbance of the chromaticity-removed water at the second wavelength represents the chromaticity of the chromaticity-removed water.

[0048] Optimizing the amount of aluminum-based coagulant added based on the chromaticity measured by the first colorimeter 6 is a feedforward control of the addition of aluminum-based coagulant. The chromaticity measured by the second colorimeter 15 is used to monitor the chromaticity of the treated water obtained as a result of adding the aluminum-based coagulant. If chromaticity removal is insufficient, the amount of coagulant added is adjusted (corrected) based on the chromaticity measured by the second colorimeter 15.

[0049] <Coagulation sedimentation treatment> The color-treated water is transferred to the coagulation and sedimentation tank 19, where a polymer coagulant is added to enlarge the coagulated flocs. In addition to the polymer coagulant, floc-forming aids, alkaline agents (e.g., slaked lime, sodium hydroxide, soda ash, etc.), and / or coagulation aids may also be added to the color-treated water, thereby more reliably removing suspended solids (SS) derived from biological treatment, including microorganisms. A portion of the coagulated and settled sludge obtained in the coagulation and sedimentation tank 19 may be returned to the color-treated tank 10. This allows for stable and enlargement of the coagulated flocs in the coagulation and sedimentation tank 19, enabling good solid-liquid separation.

[0050] <Sludge Treatment> The coagulated and settled sludge obtained from the coagulation and settling treatment is transferred to the sludge treatment device 21 and dewatered. The separated water obtained from the sludge treatment device 21 is returned to the biological treatment tank 1 for retreatment of the chromatic components. Generally, the chromaticity of the separated water is lower than that of the organic wastewater introduced into the biological treatment tank 1. By returning the separated water to the biological treatment tank 1, the organic wastewater in the biological treatment tank 1 is diluted, and the chromaticity of the organic wastewater decreases. As a result, the amount of aluminum-based coagulant that needs to be added can be reduced.

[0051] According to the embodiment described above, the residual aluminum in the chromatic treatment water is kept below 1 mg / L. Therefore, even when the separated water obtained from the sludge treatment device 21 is returned to the biological treatment tank 1, the aluminum concentration in the biological treatment tank 1 can be kept low, and the accumulation of aluminum in the activated sludge in the biological treatment tank 1 is suppressed. By suppressing the accumulation of aluminum in the activated sludge, the filterability of the sludge is improved, filamentous bulking is suppressed, and nutrients in the biological treatment tank 1 are maintained, resulting in stable biological treatment.

[0052] Furthermore, by optimizing the amount of aluminum-based coagulant added, excessive addition of aluminum-based coagulant can be suppressed even in situations where the influent water quality changes frequently, thereby reducing the cost of aluminum-based coagulant and the amount of sludge generated. In addition, by monitoring the color with a second colorimeter 15, it is possible to reliably comply with the management standards for effluent.

[0053] Next, another embodiment of the chromaticity removal device will be described with reference to Figure 2. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described above with reference to Figure 1, so a redundant explanation will be omitted.

[0054] The color removal device shown in Figure 2 includes a membrane bioreactor (MBR tank) 27 that performs the membrane bioreactor activated sludge method as a biological treatment device. This membrane bioreactor (MBR tank) 27 is configured to produce biologically treated water from which organic matter and turbidity have been removed by performing the membrane bioreactor activated sludge method on organic wastewater. The membrane bioreactor (MBR tank) 27 not only performs biological treatment but also has a filtration function that removes turbidity such as suspended solids (SS), so the solid-liquid separator 2 and the first filter 5 shown in Figure 1 are unnecessary. As a result, the color removal device can be made more compact.

[0055] The chromaticity removal system equipped with a membrane bioreactor (MBR) tank 27 allows for a higher concentration of activated sludge suspended solids (MLSS) compared to when using a sedimentation tank. Maintaining a high MLSS concentration in the membrane bioreactor (MBR) tank 27 makes chromaticity removal in the biological treatment process more effective, and the chromaticity of the biologically treated water flowing into the chromaticity treatment tank 10 can be reduced. Lowering the chromaticity of the treated material reduces the amount of aluminum-based coagulant that needs to be added.

[0056] Next, we will explain the results of the chromaticity removal treatment for organic wastewater. (Example 1) The color removal treatment of organic wastewater was performed using the color removal apparatus shown in Figure 2. Drinking wastewater with a color of 300 degrees was used as the organic wastewater, and biological treatment was performed on this organic wastewater in a membrane separation tank 27 using a membrane separation activated sludge method to obtain biologically treated water. This biological treatment using a membrane separation activated sludge method used a hollow fiber membrane with an effective filtration diameter of 0.4 μm, and therefore included a filtration process similar to that performed by the first filter 5 shown in Figure 1. The absorbance at a wavelength of 470 nm was measured using the first colorimeter 6 to determine the color of the biologically treated water. Furthermore, the amount of aluminum chloride added as an aluminum-based coagulant was determined from the color measurement results.

[0057] The obtained biologically treated water was transferred to a chromaticity treatment tank 10, and the pH was adjusted with sulfuric acid and sodium hydroxide to a pH of 7.0. A predetermined amount of aluminum chloride was added while stirring the biologically treated water with a stirrer installed in the chromaticity treatment tank 10. Then, a portion of the chromaticity treated water from the chromaticity treatment tank 10 was taken and filtered through a filter 12 with a 0.4 μm hollow fiber membrane. After that, the absorbance at a wavelength of 390 nm was measured using a second chromatometer 15 to determine the chromaticity of the chromaticity treated water.

[0058] Figure 3 is a table showing the results of the chromaticity removal treatment. The chromaticity of the biologically treated water was measured with the first chromatometer 6 and was found to be between 122 and 158 degrees. From this measurement, the required amount of aluminum chloride to be added was calculated to be 58 to 82 mg / L. When the amount of aluminum chloride added was controlled to fall within this range, the chromaticity after chromaticity treatment was between 49 and 67 degrees, which was below the management standard of 100 degrees. In addition, the aluminum concentration in the chromaticity-treated water was approximately 0.1 mg / L, which was below the management standard of 1 mg / L. The aluminum hydroxide content of the activated sludge in the biological treatment tank 1 was 5 to 8%, and the amount filtered by the filter paper in 5 minutes, which is an indicator of sludge filterability evaluation, was 20 to 28.4 mL. Since a filter paper filtration amount of 10 mL or more in 5 minutes is considered to indicate good sludge filterability, it was shown that the chromaticity removal device and chromaticity treatment method of this embodiment maintain good sludge filterability.

[0059] (Comparative Example 1) As shown in Figure 4, organic wastewater was treated for color removal using a conventional color removal method without the use of a colorimeter. When biologically treated water with a color of 122-158 degrees was treated with a constant aluminum chloride addition of 105 mg / L, the color of the treated water became 38-45 degrees, which was below the management standard of 100 degrees. However, the aluminum concentration in the color-treated water was 0.4-1.4 mg / L. When the color of the biologically treated water was low, the amount of coagulant was excessive, and the aluminum concentration in the color-treated water exceeded the management standard of 1 mg / L. At this time, the aluminum hydroxide content of the activated sludge in biological treatment tank 1 was 20-30%, and deterioration of treated water quality and bulking were confirmed. In addition, the amount of filter paper filtered in 5 minutes, which is an indicator of sludge filterability evaluation, was 4.7-8.2 mL, indicating poor sludge filterability.

[0060] In Example 1, compared to Comparative Example 1, the amount of coagulant added was reduced by 22-45% by changing the amount of coagulant added according to the chromaticity of the organic wastewater, demonstrating that the chromaticity removal treatment of the present invention can reduce treatment costs. Furthermore, the aluminum content in the activated sludge in the membrane bioreactor (MBR) tank 27 decreased, and the filamentous bulking phenomenon was eliminated by suppressing the occurrence of filamentous organisms. It became possible to maintain a constant MLSS concentration in the membrane bioreactor 27, which also led to the stabilization of biological treatment.

[0061] The embodiments described above are intended to enable persons with ordinary skill in the art to implement the present invention. Various modifications of the above embodiments can be made naturally by those skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments as well. Therefore, the present invention is not limited to the embodiments described, but is to be interpreted in the broadest sense according to the technical idea defined by the claims. [Explanation of symbols]

[0062] 1. Biological treatment tank 2 Solid-liquid separation tank 5. First filter 6 1st chromaticity meter 7 Control device 8. Aluminum-based flocculant addition device 10 Chromaticity treatment tank 12. Second filter 15 Second chromaticity meter 11. Sludge return line 17. Polymer flocculant addition device 19. Coagulation and sedimentation tank 21 Sludge treatment equipment 22 Separated water return line 27 Membrane separation tank (MBR tank)

Claims

1. By biologically treating organic wastewater in a biological treatment tank, biologically treated water is produced from which organic matter has been removed from the organic wastewater. The biologically treated water is filtered through the first filter. The color of the biologically treated water filtered by the first filter is measured with a first colorimeter. The amount of aluminum-based flocculant to be added is determined based on the chromaticity measured by the first colorimeter. The determined amount of aluminum-based coagulant is added to the biologically treated water to produce color-treated water. The color-treated water is filtered through a second filter. The chromaticity of the color-treated water filtered by the second filter is measured with a second colorimeter. The amount of aluminum-based flocculant added is adjusted based on the chromaticity measured by the second colorimeter. A method for removing the color of organic wastewater, wherein the first colorimeter measures the absorbance at a first wavelength, and the second colorimeter measures the absorbance at a second wavelength shorter than the first wavelength.

2. By performing a membrane separation activated sludge method on organic wastewater using a membrane separator tank, biologically treated water is produced from which organic matter and turbidity have been removed from the organic wastewater. The chromaticity of the biologically treated water was measured with a first colorimeter. The amount of aluminum-based flocculant to be added is determined based on the chromaticity measured by the first colorimeter. The determined amount of aluminum-based coagulant is added to the biologically treated water to produce color-treated water. The color-treated water is filtered using a filter. The chromaticity of the chromatic treated water filtered by the filter is measured with a second colorimeter. A method for removing the color of organic wastewater, comprising adjusting the amount of aluminum-based coagulant added based on the color measured by the second colorimeter.

3. The method for removing the color of organic wastewater according to claim 2, further comprising the step of adding the adjusted amount of the aluminum-based coagulant to the subsequent biologically treated water produced in the membrane separation tank to reduce the color of the subsequent biologically treated water to 100 degrees or less.

4. The method for removing the color of organic wastewater according to claim 2, wherein the first colorimeter measures the absorbance at a first wavelength, and the second colorimeter measures the absorbance at a second wavelength shorter than the first wavelength.

5. A biological treatment tank that generates biologically treated water from which organic matter has been removed by biologically treating organic wastewater, A first filter for filtering the biologically treated water, A first colorimeter for measuring the color of the biologically treated water filtered by the first filter, A control device that determines the amount of aluminum-based flocculant to be added based on the chromaticity measured by the first colorimeter, An aluminum coagulant adding device for adding the determined amount of aluminum coagulant to the biologically treated water, A chromatic treatment tank for stirring the biologically treated water and the aluminum-based coagulant to produce chromatic treated water, A second filter for filtering the color-treated water, The system includes a second colorimeter for measuring the color of the color-treated water filtered by the second filter, The control device is configured to adjust the amount of aluminum-based flocculant added based on the chromaticity measured by the second colorimeter. A color removal device for organic wastewater, wherein the first colorimeter is configured to measure absorbance at a first wavelength, and the second colorimeter is configured to measure absorbance at a second wavelength shorter than the first wavelength.

6. A membrane separation tank that produces biologically treated water from which organic matter and turbidity have been removed by performing a membrane separation activated sludge method on organic wastewater, A first colorimeter for measuring the color of the biologically treated water, A control device that determines the amount of aluminum-based flocculant to be added based on the chromaticity measured by the first colorimeter, An aluminum coagulant adding device for adding the determined amount of aluminum coagulant to the biologically treated water, A chromatic treatment tank for stirring the biologically treated water and the aluminum-based coagulant to produce chromatic treated water, A filter for filtering the color-treated water, The system includes a second colorimeter for measuring the color of the color-treated water filtered by the aforementioned filter, A color removal device for organic wastewater, wherein the control device is configured to adjust the amount of aluminum-based coagulant added based on the color measured by the second colorimeter.

7. The organic wastewater color removal apparatus according to claim 6, wherein the first colorimeter is configured to measure absorbance at a first wavelength, and the second colorimeter is configured to measure absorbance at a second wavelength shorter than the first wavelength.

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