Wastewater treatment method and wastewater treatment device

Abstract

This wastewater treatment device for biologically treating organic wastewater is provided with: a reaction tank (10) for biologically treating raw water, which is organic wastewater; an adding means (a nutrient storage tank (21) and a pump (23)) for adding a nutrient to the raw water; a VOC sensor (30) that measures the concentration of volatile organic compounds in the gas released from the water in the reaction tank (10); and a control device (40) for controlling the addition amount of the nutrient substance added by the addition means on the basis of the measured value of the concentration obtained by the VOC sensor (30).

Description

Technical Field

[0001] The present invention relates to a wastewater treatment method and a wastewater treatment device for treating organic wastewater by biological treatment. Background Art

[0002] As a drainage treatment carried out before the drainage containing organic matter, i.e., organic drainage, is released into the environment, a biological treatment using microorganisms is usually implemented. In biological treatment, in order to highly maintain the decomposition activity of organic matter based on microorganisms, it is necessary to optimize environmental conditions such as water temperature and pH, and add nutrients such as nitrogen, phosphorus, and trace metals. Compared with the drainage in the public sewers that flow into domestic drainage, the drainage from factories is prone to lack of nutrients. In particular, in the drainage from chemical plants and semiconductor manufacturing plants, the lack of nutrients required for biological treatment is significant.

[0003] It is recommended that the amount of nutrients added to the raw water as organic wastewater is proportional to the organic matter concentration in the raw water. The organic matter concentration in the raw water is expressed as the biochemical oxygen demand (BOD) concentration, and the preferred addition amounts of nitrogen (N) and phosphorus (P) as nutrients in the wastewater treatment based on aerobic microorganisms, i.e., aerobic treatment, are, for example, BOD:N:P=100:5:1 on a mass basis. Although it is difficult to measure the BOD concentration of raw water online or in a short period of time, it is possible to measure the total organic carbon (TOC) concentration in the water online. Therefore, for example, Patent Document 1 discloses the following: the correlation between the TOC concentration and the BOD concentration in the raw water is obtained in advance, and the TOC concentration of the raw water is converted into a BOD concentration value based on the TOC concentration meter being used to monitor it online, and the addition amounts of nitrogen and phosphorus are controlled based on the obtained BOD concentration value.

[0004] When volatile organic compounds (VOCs) are contained in the raw water as organic wastewater, or when volatile organic compounds are generated as intermediate metabolites during the biological treatment of organic wastewater, the volatile organic compounds in the water may be transferred to the gas phase due to aeration, etc., depending on the conditions of the biological treatment. Since volatile organic compounds are also air pollutants, it is necessary to reduce their emission into the atmosphere as much as possible. When the emission of volatile organic substances is large, it is necessary to install an exhaust gas treatment device. When optimizing the amount of nutrients added in biological treatment, it is also necessary to consider reducing the emission of volatile organic compounds.

[0005] It is known that when aerobic treatment is performed based on biological treatment, the BOD volume load in the wastewater treatment device can be increased by using a carrier in the reaction tank, but the amount of excess sludge generated in this case increases. Patent Document 2 discloses that as a technology for suppressing the amount of excess sludge generated without reducing the BOD removal rate, control is performed so that the dissolved phosphorus concentration in the reaction tank is maintained at 0.5 mg / L or less and the dissolved nitrogen concentration in the reaction tank is maintained at 3 mg / L or more.

[0006] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2001-334285 Patent Document 2: Japanese Patent Application Publication No. 2022-42384 Summary of the invention

[0007] Technical problem to be solved by the invention The method of controlling the amount of added nutrients based on the online measured TOC concentration has the following technical problem: the pipe of the online TOC concentration meter is clogged due to the accumulation of suspended solids (SS), oil, formation of biofilm, etc., and the measured value becomes unstable.

[0008] An object of the present invention is to provide a wastewater treatment method and a wastewater treatment apparatus capable of stably determining an optimum amount of nutrients to be added to raw water as organic wastewater in biological treatment of organic wastewater.

[0009] Technical solutions for solving technical problems A wastewater treatment method according to one embodiment of the present invention is a wastewater treatment method for biologically treating raw water as organic wastewater in a reaction tank, the method comprising: a concentration measuring step for measuring at least the concentration of volatile organic compounds in a gas released from water in the reaction tank; and a control step for controlling the amount of nutrients added to the raw water based on the concentration measurement value obtained in the concentration measuring step.

[0010] A wastewater treatment device according to one embodiment of the present invention comprises: a reaction tank for biologically treating raw water as organic wastewater; an addition unit for adding nutrients to the raw water; a concentration measuring unit for measuring at least the concentration of volatile organic compounds in the gas released from the water in the reaction tank; and a control unit for controlling the amount of nutrients added by the addition unit based on the concentration measurement value obtained by the concentration measuring unit.

[0011] When the biological treatment carried out in the reaction tank is an aerobic treatment, the carbon dioxide contained in the gas generated by the water in the reaction tank can be used to estimate the organic concentration in the raw water by measuring the carbon dioxide concentration, and the amount of nutrients added can be controlled according to the estimated organic concentration. However, when the organic concentration varies, especially when there is a sharp increase in the organic concentration, when the amount of nutrients added is controlled only by the carbon dioxide concentration as an indicator, the result is that the amount of nutrients added is insufficient. According to the knowledge obtained by the inventors of the present invention, when the raw water is an organic wastewater containing volatile organic compounds, or when volatile organic compounds are generated as intermediate metabolites based on biological treatment, if the amount of nutrients added is insufficient, these volatile organic compounds accumulate in the reaction tank, and the concentration of volatile organic compounds contained in the gas discharged from the reaction tank increases. Therefore, in the present invention, by measuring the concentration of volatile organic compounds contained in the gas generated by the water in the reaction tank and controlling the amount of nutrients added based on the volatile organic compound concentration, the amount of nutrients added can be further optimized, and the discharge amount of volatile organic compounds can be further reduced. The control here is, for example, to increase the amount of nutrients added if the concentration of volatile organic compounds increases, and to reduce the amount of nutrients added if the concentration of volatile organic compounds decreases. In the case where the concentration of volatile organic compounds in the gas generated from the water in the reaction tank shows a certain value for a period of time, the amount of nutrients added can be adjusted by temporarily reducing the amount of nutrients added by a certain amount to confirm whether the concentration of volatile organic compounds in the gas increases during this period.

[0012] In one embodiment of the present invention, the amount of nutrients added can be controlled based only on the concentration of volatile organic compounds contained in the gas generated by the water in the reaction tank, or the volatile organic compound concentration and the carbon dioxide concentration contained in the gas generated by the water in the reaction tank can be used to control the amount of nutrients added. In the case where the organic matter concentration in the raw water is estimated based on the carbon dioxide concentration contained in the gas generated by the water in the reaction tank, the tracking performance deteriorates when there is a sharp concentration change in the raw water, that is, the load changes, and there is a situation where the amount of nutrients added deviates from the optimal value. At this time, by using the control based on the carbon dioxide concentration and the control based on the volatile organic compound concentration, it is easy to maintain the optimal amount of nutrients added. For example, when the organic matter concentration in the raw water is estimated based on the carbon dioxide concentration and the amount of nutrients added is controlled, by adding nutrients when the volatile organic compound concentration contained in the gas generated by the water in the reaction tank rises, a more appropriate amount of nutrients can be added.

[0013] In addition, when aeration or gas diffusion is performed in the reaction tank, the concentration of volatile organic compounds contained in the gas generated by the water in the reaction tank may change depending on the flow rate of the gas such as air supplied to the reaction tank, so the flow rate of the gas supplied to the reaction tank or the gas released from the reaction tank may be measured, and the amount of nutrients added may be controlled based on both the measured value of the concentration and the measured value of the flow rate. In the wastewater treatment based on anaerobic microorganisms, i.e., anaerobic treatment, gas diffusion or the like cannot be performed, but in this case, the flow rate of the gas generated by the reaction tank may be measured, and the amount of nutrients added may be controlled based on both the measured value of the concentration and the measured value of the flow rate.

[0014] In the present invention, the volatile organic compounds contained in the gas generated by the water in the reaction tank may be volatile organic compounds contained in the raw water, or may be volatile organic compounds generated as intermediate metabolites in the biological treatment. The volatile organic compounds that are the subject of the present invention include, for example, alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone; aromatics such as benzene, toluene, and xylene; esters such as ethyl acetate; organic acids such as butyric acid, propionic acid, and acetic acid; and organic chlorine compounds. There are many cases where wastewater containing isopropanol is discharged from semiconductor device manufacturing plants, etc. When performing biological treatment of organic wastewater containing isopropanol, the amount of nutrients added can be controlled based on the concentration of isopropanol contained in the gas generated by the water in the reaction tank. However, in the biological treatment of isopropanol, acetone is generated as an intermediate metabolite, and acetone is more volatile than isopropanol. Therefore, it is easy to control the amount of nutrients added based on the concentration of acetone contained in the gas generated by the water in the reaction tank. Furthermore, when the types of organic substances contained in the organic wastewater become clear, the total concentration of volatile organic compounds can be obtained without identifying the types of volatile organic compounds contained in the gas generated from the water in the reaction tank, and the amount of nutrients added can be controlled based on the concentration.

[0015] In the present invention, various units can be used as units for measuring the concentration of volatile organic compounds. For example, manual measurement based on a detection tube can be performed, and online measurement based on equipment can also be performed. As a measurement method based on equipment, for example, there are the following methods: a method using a photoionization detector (PID: Photo-Ionization Detector), a method using a hydrogen flame ionization detector (FID: Flame-Ionization Detector), infrared absorption spectroscopy, interference amplification reflection method (Interference Enhanced Reflection: IER method) based on swelling of a polymer film, a method combining a catalyst oxidation and a carbon dioxide sensor, a method using a semiconductor gas sensor, gas chromatography, etc.

[0016] In the present invention, nutrients refer to substances required for the survival and proliferation of microorganisms, that is, nutrients such as nitrogen and phosphorus, trace elements such as iron and manganese, etc. Furthermore, in the present invention, although it cannot be said that nutrients are indispensable for the survival and proliferation of microorganisms, nutrients also include substances that promote biological treatment as co-metabolites. As an example, it is known that when organic chlorine compounds such as trichloroethylene, which are also volatile organic compounds, are used as treatment objects, the decomposition of organic chlorine compounds based on biological treatment can be promoted by adding methane, phenol, etc. as co-metabolites, and the present invention can also be used to optimize the addition amount of such co-metabolites.

[0017] Effects of the Invention According to the present invention, in biological treatment of organic wastewater, it is possible to stably determine the optimum amount of nutrients to be added to raw water as organic wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a figure which shows the wastewater treatment apparatus which concerns on one Embodiment.

[0019] Figure 2 It is a diagram showing a wastewater treatment device according to another embodiment.

[0020] Figure 3 It is a diagram showing a wastewater treatment device according to still another embodiment.

[0021] Figure 4 It is a diagram showing a wastewater treatment device according to still another embodiment. DETAILED DESCRIPTION

[0022] Next, embodiments of the present invention will be described with reference to the drawings.

[0023] The present invention relates to a technology for biologically treating raw water as organic wastewater using microorganisms and decomposing and removing organic matter in the raw water. The organic wastewater to which the present invention is applied is not particularly limited as long as it can be biologically treated, and includes, for example, wastewater in public sewers, wastewater discharged from various factories such as food factories, chemical factories, semiconductor manufacturing factories, liquid crystal manufacturing factories, pulp factories, and wastewater discharged from businesses in other fields. Compared with wastewater in public sewers, wastewater from private factories is prone to lack of nutrients required to maintain the decomposition activity of microorganisms used in biological treatment at a high level. In particular, the lack of nutrients is significant in wastewater from chemical factories, semiconductor manufacturing factories, and liquid crystal manufacturing factories. When an external organic source such as methanol is added to inorganic nitric acid wastewater (or inorganic nitrous acid wastewater) that does not contain organic matter for denitrification treatment, the wastewater to which the external organic source is added is also organic wastewater to which the present invention is applied. The biological treatment in the present invention includes aerobic treatment, anaerobic treatment, denitrification treatment, etc., and these biological treatments are performed by an activated sludge process, a membrane separation activated sludge process (Membrane Bioreactor: MBR), a biofilm process based on a fluidized bed or fixed bed, or a granular process, etc.

[0024] In the wastewater treatment method based on the present invention, in order to optimize the amount of nutrients added to the raw water, the BOD concentration or TOC concentration of the raw water is not directly measured, but at least the concentration of volatile organic compounds in the gas released by the water in the reaction tank is measured. Then, based on the measured concentration, the amount of nutrients added to the raw water is controlled. In addition to the concentration of volatile organic compounds, the concentration of carbon dioxide in the gas released by the water in the reaction tank can also be measured, and the amount of nutrients added to the raw water can be controlled based on the carbon dioxide concentration. Based on the measured carbon dioxide concentration, the organic matter concentration in the raw water, such as the BOD concentration value, can also be calculated. When calculating the organic matter concentration in the raw water based on the carbon dioxide concentration, the control of the amount of nutrients added based on the calculated organic matter concentration can be performed as the main control, and when the volatile organic compound concentration increases, the control of increasing the amount of nutrients added can be performed.

[0025] In the case where the wastewater treatment is an aerobic treatment, a gas such as air is blown into the reaction tank for aeration or gas diffusion. If the flow rate of the gas supplied to the reaction tank changes, even if the amount of volatile organic compounds and carbon dioxide produced in the reaction tank is the same, the concentration will also change. Furthermore, the amount of volatile organic compounds and carbon dioxide produced in the reaction tank changes corresponding to the flow rate of the gas supplied to the reaction tank, and the concentration may also change accordingly. Even in the case of anaerobic treatment, the flow rate of the gas generated by the water in the reaction tank itself sometimes changes. Therefore, in the wastewater treatment method based on the present invention, the flow rate of the gas supplied to the reaction tank or the gas released by the reaction tank can also be measured. When measuring the flow rate of the gas, the amount of nutrients added to the raw water can be controlled based on the measured value of the concentration and the measured value of the flow rate, and the amount of nutrients added to the raw water can also be controlled based on the value obtained by multiplying the measured value of the concentration and the measured value of the flow rate. Furthermore, the water quality of the water in the reaction tank, for example, pH, may be measured, and the amount of nutrients added to the raw water may be controlled based on the measured value of the carbon dioxide concentration, the measured value of the flow rate, and the measured value of the water quality.

[0026] If the biological treatment is an aerobic treatment, the water in the reaction tank is usually diffused or aerated by blowing air into the reaction tank with a blower for air supply. Therefore, as the gas flow rate, the flow rate of air supplied from the blower to the reaction tank can be measured, or the overall flow rate of the gas released from the reaction tank can be measured. In the case of aerobic treatment using a fluidized bed, a screen is arranged in the reaction tank to separate the carrier, and air is also blown into the screen during cleaning. However, in this case, the value obtained by adding the air volume of the blower for diffused air and the air volume of the air for cleaning the screen can be used as the gas flow rate. If the biological treatment is an anaerobic treatment, the overall flow rate of the gas released from the reaction tank can be measured as the gas flow rate.

[0027] Figure 1 A wastewater treatment device according to one embodiment is shown. Figure 1The wastewater treatment device shown has a fluidized bed type reaction tank 10, which stores raw water as organic wastewater and performs biological treatment of the raw water under aerobic conditions. The treated water in which organic matter is decomposed and removed based on biological treatment is discharged from the reaction tank 10. The reaction tank 10 is filled with a carrier 11, and a diffuser 12 is provided at the bottom of the reaction tank 10 for supplying oxygen, that is, for aeration and blowing air into the reaction tank 10. An inlet pipe 13 for supplying raw water to the reaction tank 10 is connected to the reaction tank 10. A gas pipe 14 for supplying air to the diffuser 12 is connected to the diffuser 12, and a blower 15 for air supply is provided in the gas pipe 14. As the carrier 11 that can be used here, for example, a plastic carrier, a sponge carrier, a gel carrier, etc. can be cited. Among them, from the viewpoint of cost and durability, a sponge carrier is preferably used. A stirring device for stirring the carrier 11 can also be provided in the reaction tank 10.

[0028] In biological treatment, in order to make microorganisms maintain their decomposition activity at a high level and proliferate, nutrients are required. When the nutrients in the raw water are insufficient, it is necessary to add nutrients to the raw water in the reaction tank 10 or in the front stage of the reaction tank 10. In the wastewater treatment device of this embodiment, a nutrient storage tank 21 for storing a nutrient solution, that is, a solution of nutrients is provided, and the nutrient storage tank 21 is connected to the inlet piping 13 via a nutrient solution piping 22. A pump 23 for feeding the nutrient solution is provided in the nutrient solution piping 22. Therefore, in the wastewater treatment device, nutrients can be added to the raw water flowing in the inlet piping 13 and supplied to the reaction tank 10, and by controlling the pump 23, the amount of nutrients added to the raw water can be controlled. Nutrients are roughly divided into nutrient salts containing nitrogen and phosphorus and trace elements that are less required than nitrogen and phosphorus. Trace elements include alkali metals such as sodium, potassium, calcium and magnesium, metals such as iron, manganese and zinc, etc. As a nitrogen source, urea and ammonium salts can be used. As a phosphorus source, phosphoric acid and phosphates can be used.

[0029] exist Figure 1In the wastewater treatment device shown, the amount of nutrients added is controlled according to the concentration of volatile organic compounds contained in the gas released from the water in the reaction tank 10 based on the biological treatment. Therefore, a VOC sensor 30 for detecting the concentration of volatile organic compounds is provided in the reaction tank 10 so as to detect the concentration of volatile organic compounds in the gas released from the water in the reaction tank 10. The reaction tank 10 is covered by a cover 16, and the VOC sensor 30 is provided in the gas phase part in the reaction tank 10 or in the piping connected to the gas phase part. Since the VOC sensor 30 needs to avoid condensation, when it is provided in the piping, a mist separator can be provided at a position directly in front of the VOC sensor 30, and the piping can be kept warm at the same time. In addition, according to the knowledge of the inventors of the present invention, even under completely aerobic conditions such as when the dissolved oxygen (DO) concentration in the water in the reaction tank 10 is 3 mg / L or more, under a BOD volume load of 1.5 kg / m 3 / day, hydrogen sulfide, which should be generated under anaerobic conditions, is also generated in the reaction tank 10. Corrosive gases such as hydrogen sulfide may corrode the VOC sensor 30, so it is necessary to remove the corrosive gas before measuring using the VOC sensor 30. As a method for removing hydrogen sulfide, for example, there is a method in which the gas transported to the VOC sensor 30 is brought into contact with iron oxide to fix the hydrogen sulfide as iron sulfide for removal.

[0030] When the reaction tank 10 is an open system, in order to reduce the influence of external gas on the measurement result, a cylindrical pipe or the like can be inserted under the water surface after minimizing the opening of the upper part of the reaction tank 10, and the VOC sensor 30 can be arranged at a position above the water surface in the pipe. As the VOC sensor 30, an appropriate sensor can be selected according to the type of volatile organic compound to be measured, and a sensor that measures the overall concentration of volatile organic compounds regardless of the type of volatile organic compounds can also be used.

[0031] Moreover, in Figure 1In the wastewater treatment device shown, an air volume meter 32 for measuring the flow rate of air flowing therein is provided in the gas pipe 14 at a position between the blower 15 and the diffuser 12. When the air supply volume by the blower 15 is constant and the influence of the flow rate fluctuation of the diffused air is small, it is not necessary to provide the air volume meter 32, but it is preferable to provide the air volume meter 32 in order to more accurately control the amount of added nutrients. It should be noted that the flow rate of the gas released from the reaction tank 10 may be measured instead of providing the air volume meter 32 in the gas pipe 14 to measure the flow rate of the air supplied to the reaction tank 10. In the case of measuring the flow rate of the gas released from the reaction tank 10, when the reaction tank 10 is completely covered by the cover 16, the air volume meter 32 may be provided in the pipe communicating with the inside of the reaction tank 10 in order to discharge the gas to the outside. When the reaction tank 10 is an open system, in order to reduce the influence of external air on the measurement results, the upper opening of the reaction tank 10 can be minimized, and a cylindrical pipe or the like can be inserted under the water surface and an air volume meter 32 can be installed in the pipe.

[0032] Next, Figure 1 The control of the amount of nutrients added in the wastewater treatment device shown in the figure is described. In this embodiment, by measuring the concentration of volatile organic compounds contained in the gas generated by the water in the reaction tank and controlling the amount of nutrients added based on the concentration of volatile organic compounds, the amount of nutrients added can be further optimized, and the discharge amount of volatile organic compounds can be further reduced. This control is, for example, if the concentration of volatile organic compounds increases, the amount of nutrients added is increased, and if the concentration of volatile organic compounds decreases, the amount of nutrients added is reduced. In addition, in the case where the concentration of volatile organic compounds in the gas generated by the water in the reaction tank shows a certain value for a period of time, it is also possible to temporarily reduce the amount of nutrients added by a certain amount to confirm whether the concentration of volatile organic compounds in the gas during this period increases, thereby adjusting the amount of nutrients added.

[0033] Phosphorus and nitrogen in the organic wastewater are taken in as nutrient sources for the organisms in the reaction tank 10. Therefore, in order to promote the proliferation of microorganisms and further promote the decomposition of organic matter, nutrients such as phosphorus sources and nitrogen sources are added to the organic wastewater in biological treatment. However, as described in Patent Document 2, if the dissolved phosphorus concentration in the water in the reaction tank 10 is high, the amount of excess sludge generated with the decomposition of organic matter increases. In order to reduce the amount of excess sludge generated, it is preferred to maintain the dissolved phosphorus concentration in the reaction tank 10 in a depleted state, specifically, maintained at 0.5 mg / L or less, and more preferably maintained at 0.1 mg / L or less. However, if the dissolved nitrogen concentration in the reaction tank 10 is in a depleted state, the BOD removal rate is greatly reduced. In order to suppress the significant reduction in the BOD removal rate, it is preferred to maintain the dissolved nitrogen concentration in the reaction tank 10 in a residual state, specifically, maintained at 3 mg / L or more, and more preferably maintained at 5 mg / L or more. Therefore, when controlling the amount of nutrients added, the control device 40 preferably determines the amount of nutrients added so that the concentration of dissolved phosphorus in the water in the reaction tank 10 becomes 0.5 mg / L or less.

[0034] Figure 2 A wastewater treatment device according to another embodiment is shown. Figure 2 The drainage treatment device shown is Figure 1 In the wastewater treatment device shown, a carbon dioxide concentration sensor 31 is provided, which measures the carbon dioxide concentration contained in the gas generated by the water in the reaction tank 10, and the measurement result of the carbon dioxide concentration sensor 31 is also transmitted to the control device 40. In this embodiment, based on the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31, the concentration of organic matter in the raw water is estimated, and the amount of nutrient addition is controlled based on the estimated value, and the amount of nutrient addition is further increased or decreased according to the concentration of volatile organic matter. As the carbon dioxide concentration sensor 31, for example, an optical, electrochemical or semiconductor carbon dioxide concentration sensor can be used, but it is particularly preferred to use a sensor based on the non-dispersive infrared absorption method (Non-Dispersive Infrared: NDIR). The measurement of carbon dioxide concentration can be performed manually (manual) or online. The carbon dioxide concentration sensor 31 is installed in the reaction tank 10 in the same manner as the VOC sensor 30. Since the carbon dioxide concentration sensor 31 also needs to avoid condensation and corrosive gases, when it is installed in the piping, a mist separator and a corrosive gas removal device can be installed directly in front of the carbon dioxide concentration sensor 31, while at the same time achieving heat insulation of the piping.

[0035] It is recommended that the amount of nutrients (i.e., nutrient salts and trace metals) added to raw water should be proportional to the organic matter concentration in the raw water, preferably the BOD concentration. For example, it is recommended that the amount of nitrogen (N) and phosphorus (P) added in aerobic treatment be set to BOD:N:P=100:5:1 on a mass basis. In this embodiment, the BOD concentration of raw water is not measured by an online TOC concentration meter, etc. Instead, the BOD concentration value of raw water is calculated based on the carbon dioxide concentration in the gas released from the water in the reaction tank 10 based on biological treatment, and the amount of nutrients added is determined based on the calculated BOD concentration value. Therefore, first, in this embodiment, the volatile organic compound concentration measured by the carbon dioxide sensor 31 is set as the input value (Xn), and the BOD concentration of raw water corresponding to the input value (Xn) is set as the output value (Yn). Based on the combination of a certain number of input values ​​and output values ​​obtained in advance, a model (or a relational expression) is created. The number of combinations obtained is, for example, tens to hundreds of groups. When not only the carbon dioxide concentration but also the air volume is measured by the air volume meter 32, a combination of the measured values ​​of the carbon dioxide concentration and the air volume can be set as the input value (Xn), or a value obtained by multiplying the measured value of the carbon dioxide concentration and the measured value of the air volume, that is, a multiplied value can be set as the input value (Xn).

[0036] Once the model is created, the measured value of the carbon dioxide concentration measured by the carbon dioxide sensor 31 or the combination of the measured value of the carbon dioxide concentration measured by the carbon dioxide sensor 31 and the measured value of the air volume obtained by the air volume meter 32 is input to the model, and the pump 23 is driven based on the BOD concentration value output from the model as a result, and the presence or absence of the addition of nutrients to the raw water and the amount of the nutrients added are controlled. In order to perform such control, the wastewater treatment device includes a control device 40, which holds the created model, applies the carbon dioxide concentration value obtained by the carbon dioxide sensor 31 and the measured value obtained by the air volume meter 32 to the model to calculate the BOD concentration value of the raw water, and controls the start and stop of the pump 23 and the flow rate based on the BOD concentration value. It should be noted that although the BOD concentration is used in the creation of the model, it is considered that the created model itself is a model that directly outputs the amount of nutrients added by taking the carbon dioxide concentration as an input or taking the measured value of the carbon dioxide concentration and the measured value of the air volume as an input.

[0037] Once the model is created, the optimal amount of nutrients to be added can be determined based on the measured value of carbon dioxide concentration, or based on the measured value of carbon dioxide concentration and the measured value of air volume, without explicitly calculating the BOD concentration value. In the second embodiment, on the basis of the control of adding nutrients to raw water by determining the optimal amount of nutrients to be added based on the measured value of carbon dioxide concentration, when the volatile organic compound concentration measured by the VOC sensor 30 increases, the nutrients are added to the raw water, and when the increased volatile organic compound concentration decreases, the amount of nutrients added to the raw water is reduced. In this way, the amount of nutrients added can be further optimized, and the amount of volatile organic compound release can be reduced.

[0038] Next, the creation of the model is described. The model can be created using, for example, various regression analyses, and the model outputs the BOD concentration of raw water as an output value, and the BOD concentration of the raw water corresponds to the input value at the time of input. In particular, if the model is created by supervised learning using a neural network technique, the accuracy of the control of the amount of nutrient addition is improved. The concentration of volatile organic compounds obtained by the carbon dioxide sensor 31 sometimes varies depending on the structure and size of the reaction tank 10, the size of the gas phase in the reaction tank 10, the type of biological treatment, etc., and the air volume supplied to the reaction tank 10 for gas dispersion also varies depending on the structure and size of the reaction tank 10, so the model can be set for each type of reaction tank 10. Furthermore, since the relationship between the BOD concentration of raw water and the measured carbon dioxide concentration and air volume may also vary depending on the type or origin of the raw water, it is also possible to prepare a model according to the type and origin of the raw water, and select a model for controlling the amount of nutrient addition corresponding to the type or origin of the raw water from the prepared model.

[0039] In order to control the amount of nutrients added to the raw water, it is also considered to use an online TOC concentration meter to measure the organic concentration in the raw water online, but the online TOC concentration meter has a thin pipe to introduce a small amount of sample water into the measuring device, which is prone to clogging and unstable measurement values. In contrast, the carbon dioxide sensor 31 performs measurement without contacting water, so the stability of the measurement value is very high. In addition, the gas flow rate can also be measured stably. Therefore, in the wastewater treatment device of this embodiment, it is possible to stably find the optimal value of the amount of nutrients added to the raw water without directly measuring the organic concentration in the raw water.

[0040] Figure 3 A wastewater treatment device according to still another embodiment is shown. Figure 3 The drainage treatment device shown is Figure 2In the wastewater treatment device shown, a water quality measuring unit 33 is provided, which measures the water quality of the water in the reaction tank 10, and the measurement result of the water quality measuring unit 33 is set to be transmitted to the control device 40. The water quality items measured by the water quality measuring unit 33 include at least pH, and in addition to pH, water temperature and the like can also be measured. The model used in the wastewater treatment device of this embodiment is a model in which a combination of a volatile organic compound concentration, a carbon dioxide concentration measured by a carbon dioxide sensor 31, and a water quality (especially pH) value measured by the water quality measuring unit 33 is set as an input (Xn), and a BOD concentration of raw water corresponding to the input value (Xn) is set as an output value (Yn), and is created in the same manner as the above-mentioned model. As the value of water quality, it is preferable to use a pH value. In addition, in addition to the volatile organic compound concentration, carbon dioxide concentration, and water quality values, the measured value of the air volume obtained by the air volume meter 32 can also be combined as an input (Xn) as needed. The control device 40 applies the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 and the water quality (particularly pH) value measured by the water quality measuring unit 33 to the model to calculate the BOD concentration value of the raw water, and controls the pump 23 based on the BOD concentration value. The control device 40 may also apply the value of the air volume obtained by the air volume meter 32 to the model in addition to the carbon dioxide concentration and the water quality value to calculate the BOD concentration value of the raw water as needed. Next, when the control device 40 controls the pump 23 based on the BOD concentration value, when the volatile organic compound concentration measured by the VOC sensor 30 increases, the pump 23 is controlled so that the amount of nutrients added becomes larger, and when the increased volatile organic compound concentration decreases, the pump 23 is controlled so that the amount of nutrients added is reduced.

[0041] As is known to all, in water, the form of inorganic carbonic acid changes according to pH into free carbonic acid (CO2), bicarbonate ions (HCO3 - ), carbonate ions (CO3 2- Therefore, even if the concentration of organic matter in the raw water is the same, the concentration of carbon dioxide in the gas released from the water in the reaction tank 10 may change according to the pH. Figure 3 In the wastewater treatment device shown, since the amount of nutrients added is controlled by also considering the pH of the water in the reaction tank 10, the amount of nutrients added can be optimized regardless of the pH of the raw water. In addition, the solubility of carbon dioxide in water depends on the water temperature. If the solubility of carbon dioxide changes, the concentration of carbon dioxide in the gas released from the water in the reaction tank 10 also changes. Therefore, when there is a change in water temperature in the reaction tank 10, the water temperature is measured in addition to the pH in the water quality measurement unit 33, and the amount of nutrients added can be controlled based on the water temperature in addition to the volatile organic compound concentration, carbon dioxide concentration and pH.

[0042] In wastewater treatment, a plurality of reaction tanks for biological treatment are sometimes connected in series, and treated water discharged from a preceding reaction tank is introduced into a subsequent reaction tank. By performing biological treatment in each reaction tank, treated water with a high degree of organic matter removal is obtained. Figure 4 is with Figure 1 , Figure 2 The device shown in the figure is a wastewater treatment device that performs wastewater treatment based on aerobic treatment in the same manner, and shows a wastewater treatment device in which a plurality of reaction tanks 10 are arranged in series, i.e., in multiple stages. When the reaction tanks 10 are arranged in multiple stages of two or more, in the reaction tank 10 at the front stage, the concentration of volatile organic compounds in the gas released from the reaction tank is measured, and the BOD concentration value of the raw water is calculated based on the obtained measured value, and based on the BOD concentration value, the amount of nutrients added to the raw water supplied to the reaction tank can be controlled. Therefore, in Figure 4 In the wastewater treatment device shown, the VOC sensor 30, the carbon dioxide concentration sensor 31, and the air volume meter 32 are provided only in the reaction tank 10 at the front stage, and the nutrient solution from the nutrient storage tank 21 is added to the raw water in the inlet pipe 13 connected to the reaction tank 10 at the front stage. The control device 40 calculates the BOD concentration value of the raw water based on the measured values ​​of the carbon dioxide concentration sensor 31 and the air volume meter 32, and controls the pump 23 for feeding the nutrient solution based on the BOD concentration value. Furthermore, the control device 40 controls the amount of the additionally added nutrient substance based on the measured value of the VOC sensor 30, similarly to the second embodiment or the third embodiment.

[0043] When the reaction tanks 10 are arranged in series in two or more stages, since most of the organic matter is decomposed and removed in the reaction tank 10 of the first stage, the organic matter that must be removed in the reaction tanks 10 of the second stage and later becomes less. In addition, the microorganisms that proliferate in the reaction tank 10 of the first stage die and disintegrate, and nutrients are dissolved again. For these reasons, even if nutrients are not added to the water supplied to the reaction tanks 10 of the second stage and later, biological treatment can be performed in the reaction tanks 10 of the second stage and later, and the overall treatment performance of the wastewater treatment device can be maintained. Therefore, for the reaction tanks of the second stage and later, it is also possible not to measure the concentration of volatile organic compounds, the concentration of carbon dioxide, and the air volume.

[0044] Example Next, the present invention will be described in further detail by way of examples.

[0045] Test conditions First, the common test conditions for each example are described. Figure 1The primary reaction tank shown in the figure is used for biological treatment based on aerobic treatment of raw water as organic wastewater. Aerobic microorganisms are supported on a sponge carrier composed of a hydrophobic polyurethane resin, and such a sponge carrier is filled in the reaction tank at a bulk volume of 30% relative to the volume of the reaction tank. The retention time in the reaction tank is set to 8 hours. As raw water, wastewater containing isopropyl alcohol is used as raw water simulating organic wastewater discharged from a semiconductor manufacturing plant. The BOD concentration in the raw water is about 900 mg / L, the nitrogen (N) concentration in the raw water is less than 2 mg / L, and the phosphorus (P) concentration is less than 0.1 mg. The BOD volume load during biological treatment is about 2.8 kg / m 3 / day, the water temperature is about 20°C, the dissolved oxygen (DO) concentration of the water in the reaction tank is 2 mg / L or more, and the pH of the water in the reaction tank is 7.0 to 7.5. To diffuse air, air is supplied to the reaction tank at a flow rate of 10 L / min.

[0046] Nitrogen (N), phosphorus (P) and trace metals were added to the raw water as nutrients. When the amount of nitrogen and phosphorus added was changed, the concentration of volatile organic compounds in the gas released from the water in the reaction tank 10 was measured. Since acetone is produced as an intermediate metabolite in the biological treatment of isopropyl alcohol, the concentration of isopropyl alcohol and the concentration of acetone were measured in the measurement of the concentration of volatile organic compounds. Under any condition, the concentration of isopropyl alcohol was less than 10 ppm and was almost undetectable. Under the conditions described above, it is believed that when the reaction tank 10 is in a stable state, the soluble phosphorus component contained in the water in the reaction tank 10 is in the form of phosphoric acid.

[0047] Example 1 Phosphorus was added so as to reach 10.6 mg / L relative to the volume of the raw water in the reaction tank 10, and biological treatment was performed. As a result, the acetone concentration in the gas released from the water in the reaction tank 10 was 10 ppm. When the reaction tank 10 became stable, the phosphoric acid concentration of the water in the reaction tank 10, that is, the treated water, was measured. The result was that the phosphorus conversion value in the phosphoric acid was 2.5 mg / L in terms of phosphorus.

[0048] Example 2 Phosphorus was added to 3.4 mg / L relative to the volume of the raw water in the reaction tank 10 and biological treatment was performed. As a result, the acetone concentration in the gas released from the water in the reaction tank 10 was 50 ppm, and the phosphoric acid concentration of the treated water in a steady state was 0.02 mg / L in terms of phosphorus.

[0049] Example 3 Phosphorus was added to 4.5 mg / L relative to the volume of the raw water in the reaction tank 10, and biological treatment was performed. As a result, the acetone concentration in the gas released from the water in the reaction tank 10 was 10 ppm. The phosphoric acid concentration of the treated water in a steady state was measured and found to be 0.02 mg / L in terms of phosphorus. In Example 3, phosphorus was not added excessively, and the concentration of volatile organic compounds in the gas released from the water in the reaction tank 10 was kept low, and the concentration of dissolved phosphorus in the treated water was reduced. Table 1 summarizes the relationship between the concentration of phosphorus added to the raw water in Examples 1 to 3 and the acetone concentration measured as a volatile organic compound.

[0050] (Table 1)

[0051] Acetone is generated as an intermediate metabolite in the biological treatment of isopropyl alcohol, but from the above results, it can be seen that when the biological treatment is not completed, that is, when the treatment is poor, acetone accumulates in the reaction tank 10, which can be detected as an increase in the acetone concentration in the gas phase. If the concentration of phosphorus added is increased, the acetone concentration is also reduced. Therefore, the concentration of volatile organic compounds such as acetone released from the water in the reaction tank 10 is measured. When the concentration tends to increase, the amount of nitrogen and phosphorus added is increased, and when the concentration tends to decrease, the amount of addition is also reduced. It can be seen that it can be suppressed to the minimum amount of addition required for nutrients, that is, the optimization of the amount of addition can be achieved.

[0052] Explanation of symbols 10 Reaction tank 11 Carrier 12. Air Diffuser 13 Inlet piping 14 Gas piping 15 Blower 16 Cover 21 Nutrient storage tank 22 Nutrient solution piping 23 Pump 30 VOC Sensors 31. Carbon dioxide concentration sensor 32 Air flow meter 33 Water Quality Measurement Department 40 Control device.

Claims

1. A method for treating wastewater, wherein raw water as organic wastewater is biologically treated in a reaction tank, the method comprising: a concentration measuring step of at least measuring the concentration of volatile organic compounds in the gas released from the water in the reaction tank; and The control step controls the amount of nutrients added to the raw water based on the measured value of the concentration obtained in the concentration measuring step.

2. The wastewater treatment method according to claim 1, wherein: In the concentration measuring step, in addition to measuring the concentration of the volatile organic compound, the concentration of carbon dioxide in the gas released from the water in the reaction tank is measured.

3. The wastewater treatment method according to claim 1 or 2, wherein: The wastewater treatment method further comprises a flow measurement step in which the flow rate of the gas supplied to the reaction tank or the flow rate of the gas released from the reaction tank is measured. In the control step, the amount of the nutrient added to the raw water is controlled by using the measured value of the flow rate obtained in the flow measurement step in addition to the measured value of the concentration obtained in the concentration measurement step.

4. The wastewater treatment method according to claim 1 or 2, wherein: The volatile organic compound whose concentration is measured in the concentration measuring step is at least one of a volatile organic compound contained in raw water and a volatile organic compound generated as an intermediate metabolite in the biological treatment.

5. The wastewater treatment method according to claim 1 or 2, wherein: During the biological treatment, the dissolved phosphorus concentration in the reaction tank is maintained at 0.5 mg / L or less.

6. The wastewater treatment method according to claim 1 or 2, wherein: When a plurality of the reaction tanks are arranged in series, the concentration measurement process is performed on the front-stage reaction tank, and in the control process, the amount of the nutrient added to the raw water supplied to the front-stage reaction tank, or the amount of the nutrient added to the raw water in the front-stage reaction tank, is controlled.

7. A drainage treatment device, comprising: A reaction tank for biologically treating raw water as organic wastewater; an adding unit, which adds nutrients to the raw water; a concentration measuring unit for measuring at least the concentration of volatile organic compounds in the gas released from the water in the reaction tank; as well as A control unit controls the amount of the nutrient added by the adding unit based on the measured value of the concentration obtained by the concentration measuring unit.

8. The drainage treatment device according to claim 7, wherein: The concentration measuring unit measures the concentration of carbon dioxide in the gas released from the water in the reaction tank in addition to the concentration of the volatile organic compound.

9. The wastewater treatment device according to claim 7 or 8, wherein: The control unit performs control to maintain the dissolved phosphorus concentration in the reaction tank at 0.5 mg / L or less.

10. The wastewater treatment device according to claim 7 or 8, wherein: A plurality of the reaction tanks are arranged in series, The adding unit adds the nutrient to the raw water supplied to the first-stage reaction tank or the raw water in the first-stage reaction tank, and The concentration measuring unit is provided for the reaction tank at the front stage.

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