JP7830293B2 - Method and apparatus for removing color from organic wastewater - Google Patents

Description

This invention relates to a technology for removing the color of organic wastewater, such as food wastewater, drinking water wastewater, human waste, and septic tank sludge.

In recent years, there has been increasing demand for chromatic wastewater from the perspective of water environment conservation and safety, particularly regarding rivers and other bodies of water. For example, organic wastewater such as food wastewater, drinking water wastewater, human waste, and septic tank sludge often contains chromatic components, requiring its removal before discharge. However, wastewater generated in food and beverage manufacturing plants experiences significant fluctuations in volume and quality over short periods depending on the products and production processes, making stable chromatic treatment difficult.

In chromaticity removal treatment, a common method involves adding a coagulant to organic wastewater to coagulate and remove organic and colloidal substances that contribute to the chromaticity of the wastewater. The amount of coagulant to add is often determined based on the results of a coagulation test conducted using a jar test. However, since obtaining results from a jar test takes time, real-time reflection of the coagulant addition rate is not possible.

Figure 4 is a schematic diagram showing an example of a conventional color treatment device. Organic wastewater is first biologically treated in a biological treatment tank 501. Then, the organic wastewater is sent to a color treatment tank 502, where a coagulant is added to the organic wastewater from a coagulant additive device 503, and color treatment is performed. The color-treated organic wastewater is sent to a coagulation and sedimentation tank 504, where it is separated into coagulated sludge and coagulated treated water. The coagulated treated water is discharged as effluent. The coagulated sludge is sent to a sludge treatment device 505, where water is further separated from the coagulated sludge. The separated water is returned to the biological treatment tank 501 and treated again.

Conventional technology employs a feedback control system, as shown in Figure 4, which adjusts the amount of coagulant added after measuring the chromaticity of the effluent using a colorimetric method or spectrophotometer. However, this control method is insufficient for chromaticity removal, and the effluent chromaticity may exceed the management standard. Therefore, to prevent the effluent chromaticity 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. This leads to increased coagulant costs and sludge generation, contributing to high treatment costs.

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. Therefore, to respond without delay to the occurrence of high-chromatic wastewater, it was necessary to constantly add large amounts of aluminum-based coagulants during operation. However, the excessive addition of aluminum-based coagulants led to the following problems:

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.

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.

Japanese Patent Application Publication No. 4-193311 Japanese Patent Publication No. 2018-161632

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, 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, applying a colorimeter is difficult.

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.

When incorporating biological treatment into wastewater treatment, the impact of residual aluminum is significant. Therefore, optimizing the amount of aluminum-based coagulant added is crucial to simultaneously achieve color removal and stable wastewater treatment.

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.

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 filtered 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 in a second 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.

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 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.

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.

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 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.

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; 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 for stirring 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 added based on the color measured by the second colorimeter.

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.

In one embodiment, an organic wastewater color removal device is provided, comprising: 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 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 for stirring the biologically treated water and the aluminum-based coagulant to produce color-treated water; a filter for filtering the color-treated water; and a second colorimeter for measuring the color of the color-treated water filtered by the filter. The control device is configured to adjust the amount of aluminum-based coagulant added based on the color measured by the second colorimeter.

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 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 membrane separation tank.

According to the method and apparatus for removing chromaticity from organic wastewater according to the present invention, the amount of coagulant to be added is determined based on the chromaticity of the biologically treated water obtained by biologically treating organic wastewater, and the amount of coagulant to be added is further adjusted based on the chromaticity of the treated water after chromaticity treatment. Therefore, chromaticity can be removed from organic wastewater with the optimal coagulant. In particular, since the biologically treated water is filtered by the first filter or membrane separator before being measured by the first colorimeter, the first colorimeter can accurately measure the chromaticity of the biologically treated water from which turbidity has been removed. Similarly, since the color-treated water is filtered by the second filter before being measured by the second colorimeter, the second colorimeter can accurately measure the chromaticity of the color-treated water from which turbidity has been removed. As a result, the optimal amount of aluminum-based coagulant to be added can be determined.

This is a schematic diagram showing one embodiment of a color removal device for organic wastewater. This is a schematic diagram showing another embodiment of the chromaticity removal device for organic wastewater. This table shows the results of the chromaticity removal process. This is a schematic diagram showing an example of a conventional chromaticity removal device.

Embodiments of the present invention will be described below with reference to the drawings.
Figure 1 is a schematic diagram showing one embodiment of an organic wastewater color removal device. 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 adding device 8. It determines the amount of aluminum-based flocculant to be added based on the chromaticity measured by the first colorimeter 6, and further adjusts the amount of aluminum-based flocculant to be added based on the chromaticity measured by the second colorimeter 15.

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.

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 as needed. Biological treatment using microorganisms is carried out within the biological treatment tank 1. In one embodiment, the biological treatment tank 1 uses an activated sludge tank containing activated sludge.

In this embodiment, as shown in Figure 1, the color removal device further comprises a solid-liquid separation tank 2 for separating sludge from the biologically treated water before filtration 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 positioned 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.

The chromaticity treatment tank 10 is configured to produce chromaticity-treated water with reduced or removed chromaticity by agitating 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. The aluminum-based coagulant addition device 8 is connected to the chromaticity treatment tank 10. The biologically treated water, from which sludge has been separated in the solid-liquid separation tank 2, is introduced into the chromaticity treatment tank 10. The biologically treated water and the aluminum-based coagulant are mixed and agitated, removing organic and colloidal substances that contribute to chromaticity, thereby reducing or removing chromaticity. The aluminum-based coagulant can be any of PAC (polyaluminum chloride), aluminum chloride, or aluminum sulfate, with PAC or aluminum chloride being particularly effective in removing chromaticity.

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 a filter media made of fiber or polymer material 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.

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.

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, using membrane filtration is desirable because it allows for the clarification 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, being 0.02 to 5 μm, preferably 0.02 to 2 μm, and more preferably 0.02 to 1 μm.

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 shorter than the first wavelength used by the first colorimeter 6. The second colorimeter 15 measures absorbance at wavelengths 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 absorbance at shorter wavelengths, it is possible to measure the chromaticity of the chromaticity-treated water with high accuracy, even at low chromaticity levels.

The control device 7 is connected to the first colorimeter 6, the aluminum-based coagulant additive device 8, and the second colorimeter 15. It is configured to determine the additive 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 added. This allows the aluminum-based coagulant additive device 8 to supply the necessary amount of aluminum-based coagulant to keep the effluent below the management standard value.

The control device 7 consists of at least one computer. The control device 7 includes a storage device 7a containing a program for determining the optimal amount of aluminum-based flocculant to be added, and a processing device 7b that executes 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 the processing device 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.

The control device 7 stores a first calculation formula for determining the amount of aluminum-based flocculant to be added in its storage device 7a. The control device 7 inputs the chromaticity measured by the first colorimeter 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.

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 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.

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 while reducing the amount of aluminum-based flocculant used.

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 storage 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.

The constants c and d are predetermined based on experiments or actual operation. More specifically, they are the values obtained when the adjusted amount of aluminum-based coagulant, obtained by adding the correction amount obtained from the second calculation formula to the amount obtained from the first calculation formula, is added to the biologically treated water, such that 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.

As shown in Figure 1, the chromaticity removal apparatus of this embodiment further comprises a polymer flocculant addition 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 sediment sludge, a sludge treatment device 21 for separating water from the flocculated sediment 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.

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

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. Because 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), the separated water is returned to the biological treatment tank 1 for retreatment.

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

<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.

<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.
<First 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 by 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.

<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.

<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.

Optimizing the amount of aluminum-based coagulant added, based on the chromaticity measured by the first colorimeter 6, is a feedforward control of the aluminum-based coagulant addition. The chromaticity measured by the second colorimeter 15 is used to monitor the chromaticity of the treated water obtained after the addition of 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.

<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, a floc formation aid, an alkaline agent (e.g., slaked lime, sodium hydroxide, soda ash, etc.), and/or a coagulation aid 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.

<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.

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 maintained at a low level, and the accumulation of aluminum in the activated sludge within the biological treatment tank 1 is suppressed. By suppressing the accumulation of aluminum in the activated sludge, improvements in sludge filterability, suppression of filamentous bulking, and maintenance of nutrients within the biological treatment tank 1 are achieved, resulting in stable biological treatment.

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 using the second colorimeter 15, it is possible to reliably comply with the management standards for effluent.

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

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. Since the membrane bioreactor (MBR tank) 27 not only performs biological treatment but also has a filtration function to remove turbidity such as suspended solids (SS), the solid-liquid separation tank 2 and the first filter 5 shown in Figure 1 are unnecessary. As a result, the color removal device can be made more compact.

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, lowering the chromaticity of the biologically treated water flowing into the chromaticity treatment tank 10. A lower chromaticity of the treated material allows for a reduction in the amount of aluminum-based coagulant added.

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 device 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 the filtration treatment 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.

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

Figure 3 shows a table illustrating the results of the chromaticity removal treatment. The chromaticity of the biologically treated water was measured using 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 treatment was between 49 and 67 degrees, which was below the management standard of 100 degrees. Furthermore, 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, an indicator of sludge filterability, 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, this demonstrates that the chromaticity removal device and chromaticity treatment method of this embodiment maintain good sludge filterability.

(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 to 158 degrees was treated with a constant aluminum chloride addition of 105 mg/L, the color of the treated water became 38 to 45 degrees, which was below the management standard of 100 degrees. However, the aluminum concentration in the color-treated water was 0.4 to 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 to 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 to 8.2 mL, indicating poor sludge filterability.

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. This demonstrated that the chromaticity removal treatment of the present invention resulted in a reduction in 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. Maintaining a constant MLSS concentration in the membrane bioreactor 27 also contributed to the stabilization of the biological treatment.

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 are naturally possible for those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Therefore, the present invention is not limited to the embodiments described, but is interpreted in the broadest sense according to the technical idea defined by the claims.

1. Biological treatment tank 2. Solid-liquid separation tank 5. First filter 6. First colorimeter 7. Control device 8. Aluminum-based coagulant addition device 10. Color treatment tank 12. Second filter 15. Second colorimeter 11. Sludge return line 17. Polymer coagulant addition device 19. Coagulation and sedimentation tank 21. Sludge treatment device 22. Separated water return line 27. Membrane separation tank (MBR tank)

Claims (7)

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 . 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. 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. 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. 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 . 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. 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.