Drainage treatment method and drainage treatment device

Abstract

A wastewater treatment device that performs biological treatment of organic wastewater has a reaction tank (10) that performs biological treatment of raw water that is organic wastewater, an addition unit (a nutrient substance storage tank (21) and a pump (23)) that adds a nutrient substance to the raw water, a VOC sensor (30) that measures a concentration of volatile organic compounds in gas released from water in the reaction tank (10), and a control device (40) that controls an addition amount of the nutrient substance added by the addition unit based on a measured value of the concentration obtained by the VOC sensor (30).

Description

Technical Field

[0001] This invention relates to a wastewater treatment method and apparatus for treating organic wastewater based on biological treatment. Background Technology

[0002] Wastewater treatment, which involves releasing organic wastewater (organic wastewater) into the environment, typically employs biological treatment using microorganisms. In biological treatment, to maintain high levels of microbial activity in decomposing organic matter, environmental conditions such as water temperature and pH need to be optimized, and nutrients such as nitrogen, phosphorus, and trace metals need to be added. Compared to wastewater flowing into public sewers for domestic use, wastewater from industrial plants is often deficient in nutrients. In particular, the nutrient deficiency required for biological treatment is significant in wastewater from chemical plants and semiconductor manufacturing plants.

[0003] It is recommended that the amount of nutrients added to the raw water used for organic wastewater treatment be proportional to the concentration of organic matter in the raw water. The organic matter concentration in the raw water is set as the biochemical oxygen demand (BOD) concentration. The preferred addition amounts of nitrogen (N) and phosphorus (P) as nutrients in aerobic 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 the raw water online or within a short 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 BOD concentration in the raw water is obtained in advance; the TOC concentration of the raw water is monitored using an online TOC concentration meter; it is then converted into a BOD concentration value; and the addition amounts of nitrogen and phosphorus are controlled based on the obtained BOD concentration value.

[0004] When raw water used for organic wastewater contains volatile organic compounds (VOCs), or when VOCs are generated as intermediate metabolites during the biological treatment of organic wastewater, depending on the biological treatment process, these VOCs may sometimes be transferred to the gas phase due to aeration or other factors. Since VOCs are also air pollutants, it is essential to minimize their emissions into the atmosphere. In cases of high VOC emissions, waste gas treatment devices are necessary. Furthermore, when optimizing nutrient addition during biological treatment, minimizing VOC emissions must also be considered.

[0005] It is known that in aerobic treatment based on biological treatment, the BOD volumetric load in the wastewater treatment device can be increased by using a carrier in the reaction tank, but this also increases the amount of residual sludge produced. Patent Document 2 discloses the following: as a technique for suppressing the amount of residual sludge produced without reducing the BOD removal rate, control is performed to maintain the dissolved phosphorus concentration in the reaction tank below 0.5 mg / L and the dissolved nitrogen concentration in the reaction tank above 3 mg / L.

[0006] Existing technical documents Patent documents 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] The technical problem that the invention aims to solve The method of controlling the amount of nutrients added based on the online measured TOC concentration has the following technical problems: the inside of the piping of the online TOC concentration meter is blocked due to the accumulation of suspended solids (SS), oil, biofilm formation, etc., making the measured value unstable.

[0008] The purpose of this invention is to provide a wastewater treatment method and a wastewater treatment apparatus that can stably determine the optimal amount of nutrients to be added to the raw water used as organic wastewater in the biological treatment of organic wastewater.

[0009] Technical solutions for solving technical problems One aspect of the present invention is a wastewater treatment method for biologically treating raw water as organic wastewater in a reaction tank. The method comprises: a concentration measurement step, which measures at least the concentration of volatile organic compounds in gases released from water in the reaction tank; and a control step, which controls the amount of nutrients added to the raw water based on the concentration measurement value obtained in the concentration measurement step.

[0010] One aspect of the wastewater treatment apparatus of the present invention comprises: a reaction tank for biological treatment of 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 gases 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 measured value obtained by the concentration measuring unit.

[0011] When the biological treatment in the reactor is aerobic, the concentration of carbon dioxide in the gas produced from the water in the reactor can be measured to estimate the concentration of organic matter in the raw water, and the amount of nutrients added can be controlled based on the estimated organic matter concentration. However, when the organic matter concentration fluctuates, especially when there is a sharp increase in the organic matter concentration, controlling the amount of nutrients added based solely on the carbon dioxide concentration results in insufficient nutrient addition. According to the insights obtained by the inventors of the present invention, when the raw water is 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 reactor, and the concentration of volatile organic compounds in the gas discharged from the reactor increases. Therefore, in the present invention, by measuring the concentration of volatile organic compounds in the gas produced from the water in the reactor 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 amount of volatile organic compounds discharged can be further reduced. For example, the control here involves increasing the amount of nutrients added if the concentration of volatile organic compounds (VOCs) increases, and decreasing the amount of nutrients added if the concentration of VOCs decreases. If the concentration of VOCs in the gas generated from the water in the reaction tank shows a certain value over a period of time, the amount of nutrients added can be temporarily reduced by a certain amount to confirm whether the concentration of VOCs in the gas increases during this period, thereby adjusting the amount of nutrients added.

[0012] In one aspect of the invention, the amount of nutrients added can be controlled solely based on the concentration of volatile organic compounds (VOCs) in the gas generated from the water in the reaction tank. Alternatively, both the VOC concentration and the carbon dioxide concentration in the gas generated from the water in the reaction tank can be used to control the amount of nutrients added. When the concentration of organic matter in the raw water is estimated based on the carbon dioxide concentration in the gas generated from the water in the reaction tank, the nutrient addition deteriorates when there are rapid concentration changes in the raw water, i.e., load changes, leading to deviations from the optimal value. In this case, by using both control based on carbon dioxide concentration and control based on VOC concentration, it is easy to maintain the amount of nutrients added at the optimal level. For example, when estimating the concentration of organic matter in the raw water based on the carbon dioxide concentration and controlling the amount of nutrients added, a more appropriate amount of nutrients can be set by adding nutrients when the concentration of VOCs in the gas generated from the water in the reaction tank increases.

[0013] Furthermore, when aeration and gas dispersion occur in the reaction tank, the concentration of volatile organic compounds in the gas generated from the water within the reaction tank may vary depending on the flow rate of the gas supplied to the reaction tank. Therefore, it is possible to measure the flow rate of the gas supplied to or released from the reaction tank, and control the amount of nutrients added based on both the measured concentration and flow rate. In anaerobic wastewater treatment based on anaerobic microorganisms, aeration is not feasible. However, even in this case, the flow rate of the gas generated by the reaction tank can be measured, and the amount of nutrients added can be controlled based on both the measured concentration and flow rate.

[0014] In this invention, the volatile organic compounds (VOCs) contained in the gas generated from the water in the reaction tank can be VOCs contained in the raw water or VOCs generated as intermediate metabolites during biological treatment. VOCs targeted by this 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 organochlorine compounds. Wastewater containing isopropanol is frequently discharged from semiconductor manufacturing plants, etc. When biologically treating organic wastewater containing isopropanol, the amount of nutrients added can be controlled based on the concentration of isopropanol in the gas generated from the water in the reaction tank. However, in the biological treatment of isopropanol, acetone is generated as an intermediate metabolite. Acetone is more volatile than isopropanol; therefore, it is easy to control the amount of nutrients added based on the concentration of acetone in the gas generated from the water in the reaction tank. Furthermore, when the types of organic matter contained in organic wastewater become clear, it is possible to determine the overall concentration of volatile organic compounds without identifying the types of volatile organic compounds contained in the gas generated from the water in the reaction tank, and to control the amount of nutrients added based on this concentration.

[0015] In this invention, various units can be used as the unit for determining the concentration of volatile organic compounds. For example, manual determination based on a detection tube or online determination based on a device can be performed. As a device-based determination method, there are methods such as those using a photo-ionization detector (PID), a flame-ionization detector (FID), infrared absorption spectroscopy, interference enhanced reflection (IER) based on the swelling of a polymer film, a method combining catalyst oxidation and a carbon dioxide sensor, a method using a semiconductor gas sensor, gas chromatography, etc.

[0016] In this invention, nutrients refer to substances required for the survival and proliferation of microorganisms, including nutrients such as nitrogen and phosphorus, and trace elements such as iron and manganese. Furthermore, while nutrients cannot be said to be indispensable for the survival and proliferation of microorganisms, they also include substances that promote biological treatment as co-metabolites. For example, it is known that when treating organochlorine compounds such as trichloroethylene, which are also volatile organic compounds, adding methane, phenol, etc., as co-metabolites can promote the decomposition of organochlorine compounds in biological treatment. This invention can also be used to optimize the amount of such co-metabolites added.

[0017] Invention Effects According to the present invention, in the biological treatment of organic wastewater, it is possible to stably determine the optimal amount of nutrients to be added to the raw water, which is organic wastewater. Attached Figure Description

[0018] Figure 1 This is a diagram illustrating a drainage treatment apparatus according to one embodiment.

[0019] Figure 2 This is a diagram illustrating a drainage treatment apparatus according to another embodiment.

[0020] Figure 3 This is a diagram showing a drainage treatment device according to yet another embodiment.

[0021] Figure 4 This is a diagram showing a drainage treatment device according to yet another embodiment. Detailed Implementation

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

[0023] This invention relates to a technique for biologically treating raw water containing organic wastewater using microorganisms to decompose and remove organic matter. The organic wastewater to which this invention is aimed is not particularly limited, as long as biological treatment can be applied. Examples include wastewater from public sewers, wastewater discharged from various factories such as food factories, chemical plants, semiconductor manufacturing plants, liquid crystal manufacturing plants, and pulp mills, as well as wastewater discharged from businesses in other sectors. Compared to wastewater from public sewers, wastewater from private factories often lacks the nutrients necessary to maintain the decomposition activity of the microorganisms used in biological treatment. This nutrient deficiency is particularly pronounced in wastewater from chemical plants, semiconductor manufacturing plants, and liquid crystal manufacturing plants. Wastewater from which an external organic source, such as methanol, is added for denitrification treatment of inorganic nitric acid wastewater (or inorganic nitrite wastewater) that does not contain organic matter is also considered organic wastewater to which this invention is aimed. The biological treatment in this invention includes aerobic treatment, anaerobic treatment, denitrification treatment, etc., which are carried out through activated sludge process, membrane bioreactor (MBR) process, biofilm process based on moving bed or fixed bed, or 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, instead of directly measuring the BOD or TOC concentration of the raw water, at least the concentration of volatile organic compounds (VOCs) in the gas released from 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 VOC concentration, the carbon dioxide concentration in the gas released from the water in the reaction tank can also be measured, and the amount of nutrients added to the raw water is controlled based on the carbon dioxide concentration. Based on the measured carbon dioxide concentration, the concentration of organic matter in the raw water, such as the BOD concentration, 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 primary control, and the amount of nutrients added can be increased when the VOC concentration increases.

[0025] In the case of aerobic wastewater treatment, air or other gases are blown into the reaction tank for aeration or dispersion. 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 change. Consequently, the amount of volatile organic compounds and carbon dioxide produced in the reaction tank changes according 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 produced by the water in the reaction tank itself may sometimes change. 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 from the reaction tank can also be measured. When measuring the gas flow rate, the amount of nutrients added to the raw water can be controlled either based on the measured concentration value and the measured flow rate value, or based on the value obtained by multiplying the measured concentration value and the measured flow rate value. Furthermore, the water quality in the reaction tank, such as pH, can be measured, and the amount of nutrients added to the raw water can be controlled based on the measured values ​​of carbon dioxide concentration, flow rate, and water quality.

[0026] If the biological treatment is aerobic, air is typically introduced into the reaction tank using a blower to aerate or disperse the water. Therefore, the gas flow rate can be measured as either the flow rate of the air supplied to the reaction tank by the blower or the total flow rate of the gas released from the reaction tank. In the case of aerobic treatment using a moving bed, a screen is placed in the reaction tank to separate the carrier, and air is also introduced during screen cleaning. However, in this case, the gas flow rate can be obtained by adding the air volume of the blower used for aeration to the air volume used for screen cleaning. If the biological treatment is anaerobic, the total flow rate of the gas released from the reaction tank is measured.

[0027] Figure 1 This describes a drainage treatment apparatus according to one embodiment. Figure 1The wastewater treatment apparatus shown includes a fluidized bed reactor 10, which stores raw water as organic wastewater and performs biological treatment of the raw water under aerobic conditions. Treated water, from which organic matter has been decomposed and removed through biological treatment, is discharged from the reactor 10. A carrier 11 is filled in the reactor 10, and an aeration device 12 is installed at the bottom of the reactor 10 to supply oxygen, i.e., to blow air into the reactor 10 for aeration. An inlet pipe 13 is connected to the reactor 10 to supply raw water. A gas pipe 14 is connected to the aeration device 12 to supply air, and a blower 15 for air delivery is installed in the gas pipe 14. Examples of carriers 11 that can be used here include plastic carriers, sponge carriers, and gel carriers. From the viewpoints of cost and durability, sponge carriers are preferred. A stirring device for the stirring carrier 11 can also be installed in the reactor 10.

[0028] In biological treatment, nutrients are required to maintain the high decomposition activity and proliferation of microorganisms. When nutrients are insufficient in the raw water, they need to be added to the raw water in the reaction tank 10 or in the upstream stage of the reaction tank 10. In the wastewater treatment apparatus of this embodiment, a nutrient storage tank 21 is provided to store the nutrient solution, i.e., the nutrient solution. The nutrient storage tank 21 is connected to the inlet pipe 13 via a nutrient solution pipe 22. A pump 23 for supplying the nutrient solution is installed in the nutrient solution pipe 22. Therefore, in this wastewater treatment apparatus, nutrients can be added to the raw water flowing in the inlet pipe 13 and supplied to the reaction tank 10. By controlling the pump 23, the amount of nutrients added to the raw water can be controlled. Nutrients are broadly classified into nitrogen and phosphorus-containing nutrient salts and trace elements required in smaller quantities compared to nitrogen and phosphorus. Trace elements include alkali metals such as sodium, potassium, calcium, and magnesium, and metals such as iron, manganese, and zinc. Urea and ammonium salts can be used as nitrogen sources. Phosphoric acid and phosphates can be used as phosphorus sources.

[0029] exist Figure 1In the wastewater treatment apparatus shown, the amount of nutrients added is controlled based on the concentration of volatile organic compounds (VOCs) contained in the gas released from the water in the reaction tank 10 based on biological treatment. Therefore, a VOC sensor 30 is installed in the reaction tank 10 to detect the concentration of VOCs 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 installed in the gas phase section of the reaction tank 10 or in a pipe connected to that gas phase section. Since the VOC sensor 30 needs to be protected from condensation, if it is installed in a pipe, a mist separator can be installed directly in front of the VOC sensor 30, while also providing insulation for the pipe. Furthermore, according to the inventors' understanding, even under completely aerobic conditions such as a dissolved oxygen (DO) concentration of 3 mg / L or higher in the water in the reaction tank 10, and a BOD volumetric loading of 1.5 kg / m³, 3 Under high-load conditions such as / day, hydrogen sulfide, which should be produced under anaerobic conditions, will also be generated in the reaction tank 10. Corrosive gases such as hydrogen sulfide may corrode the VOC sensor 30, so it is necessary to remove corrosive gases before using the VOC sensor 30 for measurement. As a method for removing hydrogen sulfide, for example, there is a method that removes hydrogen sulfide by contacting the gas supplied to the VOC sensor 30 with iron oxide to fix the hydrogen sulfide into iron sulfide.

[0030] In the case where the reaction tank 10 is an open system, in order to reduce the influence of external gases on the measurement results, a cylindrical pipe or the like can be inserted below the water surface while minimizing the open portion at the top of the reaction tank 10, and a VOC sensor 30 can be installed at the water surface position within this pipe. As the VOC sensor 30, an appropriate sensor can be selected based on the type of volatile organic compound being measured, or a sensor that measures the overall concentration of volatile organic compounds regardless of their type can be used.

[0031] Moreover, in Figure 1In the drainage treatment device shown, an airflow meter 32 is installed in the gas piping 14 between the blower 15 and the aeration device 12 to measure the flow rate of the air flowing there. Although the airflow meter 32 is not necessary when the air supply of the blower 15 is constant and the influence of the flow rate variation of the aeration air is small, it is preferable to install the airflow meter 32 for more precise control of the amount of nutrient added. It should be noted that the flow rate of the gas released from the reaction tank 10 can also be measured instead of installing the airflow meter 32 in the gas piping 14 to measure the flow rate of the air supplied to the reaction tank 10. When measuring the flow rate of the gas released from the reaction tank 10, if the reaction tank 10 is completely covered by the cover 16, the airflow meter 32 can be installed in the piping communicating with the interior of the reaction tank 10 to discharge the gas to the outside. In the case where the reaction tank 10 is an open system, in order to reduce the influence of external gas on the measurement results, a cylindrical pipe or the like can be inserted below the water surface while minimizing the open portion at the top of the reaction tank 10, and an air volume meter 32 can be installed in the pipe.

[0032] Next, for Figure 1 The control of the amount of nutrients added in the wastewater treatment device shown will be explained. In this embodiment, by measuring the concentration of volatile organic compounds (VOCs) contained in the gas generated from the water in the reaction tank, and controlling the amount of nutrients added based on the VOC concentration, the amount of nutrients added can be further optimized, and the amount of VOCs emitted can be further reduced. For example, if the concentration of VOCs increases, the amount of nutrients added is increased; if the concentration of VOCs decreases, the amount of nutrients added is decreased. Furthermore, if the concentration of VOCs in the gas generated from the water in the reaction tank shows a certain value over a period of time, the amount of nutrients added can be temporarily reduced by a certain amount to confirm whether the concentration of VOCs in the gas increases during this period, thereby adjusting the amount of nutrients added.

[0033] Phosphorus and nitrogen in organic wastewater are ingested as nutrients for the organisms within reaction tank 10. Therefore, from the perspective of promoting microbial proliferation and thus promoting the decomposition of organic matter, these nutrients, such as phosphorus and nitrogen sources, are added to the organic wastewater during biological treatment. However, as described in Patent Document 2, if the concentration of dissolved phosphorus in the water within reaction tank 10 is high, the amount of residual sludge generated from the decomposition of organic matter increases. To reduce the amount of residual sludge generated, it is preferable to maintain the concentration of dissolved phosphorus in reaction tank 10 at a depleted state, specifically below 0.5 mg / L, and more preferably below 0.1 mg / L. However, if the concentration of dissolved nitrogen in reaction tank 10 is depleted, the BOD removal rate decreases significantly. To suppress the significant decrease in the BOD removal rate, it is preferable to maintain the concentration of dissolved nitrogen in reaction tank 10 at a residual state, specifically above 3 mg / L, and more preferably above 5 mg / L. Therefore, when controlling the amount of nutrients added, the control device 40 preferably determines the amount of nutrients added in such a way that the concentration of dissolved phosphorus in the water in the reaction tank 10 is less than 0.5 mg / L.

[0034] Figure 2 This refers to a drainage treatment device according to another embodiment. Figure 2 The drainage treatment device shown is in Figure 1 In the wastewater treatment apparatus shown, a carbon dioxide concentration sensor 31 is provided. This sensor measures the concentration of carbon dioxide in the gas generated from 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 nutrients added is controlled based on this estimated value. Furthermore, the amount of nutrients added is adjusted according to the concentration of volatile organic compounds. As the carbon dioxide concentration sensor 31, for example, an optical, electrochemical, or semiconductor carbon dioxide concentration sensor can be used, but a sensor based on non-dispersive infrared (NDIR) absorption is particularly preferred. The measurement of carbon dioxide concentration can be performed manually 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 also achieving the insulation of the piping.

[0035] It is recommended that the amount of nutrients (i.e., nutrients and trace metals) added to the raw water be proportional to the concentration of organic matter in the raw water, preferably proportional to 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, instead of measuring the BOD concentration of the raw water using an online TOC concentration meter, the BOD concentration of the raw water is calculated based on the concentration of carbon dioxide in the gas released from the water in the reaction tank 10 during biological treatment, and the amount of nutrients added is determined based on the calculated BOD concentration. Therefore, in this embodiment, the concentration of volatile organic compounds measured by the carbon dioxide sensor 31 is set as the input value (Xn), and the BOD concentration of the raw water corresponding to the input value (Xn) is set as the output value (Yn). A model (or formula) is created based on a certain number of combinations of input and output values ​​obtained in advance. The number of combinations obtained is, for example, tens to hundreds. When measuring not only carbon dioxide concentration but also air volume based on air volume meter 32, the combination of the measured values ​​of carbon dioxide concentration and air volume can be set as the input value (Xn), or the value obtained by multiplying the measured value of carbon dioxide concentration and the measured value of air volume, i.e., the multiplied value, can be set as the input value (Xn).

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

[0037] Once the model is created, the optimal amount of nutrients can be determined based on the measured carbon dioxide concentration, or based on the measured carbon dioxide concentration and airflow rate, without explicitly calculating the BOD concentration. In the second embodiment, based on the control of adding nutrients to the raw water according to the optimal amount determined by the measured carbon dioxide concentration, when the volatile organic compound (VOC) concentration measured by the VOC sensor 30 increases, nutrients are added to the raw water; when the increasing VOC concentration decreases, the amount of nutrients added to the raw water is reduced. This further optimizes the amount of nutrients added and reduces the release of VOCs.

[0038] Next, the creation of the model will be explained. Regarding the model, various regression analyses can be used to create one that outputs the BOD concentration of the raw water as the output value, corresponding to the input value at the input. In particular, if a model is created using supervised learning via neural network technology, the accuracy of controlling the amount of nutrients added is improved. The volatile organic compound concentration 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 section in the reaction tank 10, the type of biological treatment, etc. Furthermore, the airflow supplied to the reaction tank 10 for aeration also varies depending on the structure and size of the reaction tank 10; therefore, the model can be set for each type of reaction tank 10. Furthermore, since the relationship between the BOD concentration of the raw water and the measured carbon dioxide concentration and airflow may vary depending on the type or source of the raw water, a model can also be prepared according to the type and source of the raw water, and a model for controlling the amount of nutrients added can be selected from such prepared models corresponding to the type or source of the raw water.

[0039] To control the amount of nutrients added to the raw water, an online TOC concentration meter was considered for online measurement of organic matter concentration in the raw water. However, online TOC concentration meters have thin tubing for introducing a small amount of sample water into the measuring device, which is prone to clogging and results in unstable readings. In contrast, the carbon dioxide sensor 31 measures without contact with water, thus providing highly stable readings. Furthermore, it allows for stable measurement of gas flow rate. Therefore, in the wastewater treatment apparatus of this embodiment, the optimal amount of nutrients to be added to the raw water can be reliably determined without directly measuring the organic matter concentration.

[0040] Figure 3 This refers to a drainage treatment device according to yet another embodiment. Figure 3 The drainage treatment device shown is in Figure 2The wastewater treatment apparatus shown includes a water quality measuring unit 33, which measures the water quality in the reaction tank 10 and transmits the measurement results to the control device 40. The water quality measured by the water quality measuring unit 33 includes at least pH, and may also measure water temperature, etc. The model used in the wastewater treatment apparatus of this embodiment is created similarly to the model described above, where the combination of volatile organic compound concentration, carbon dioxide concentration measured by carbon dioxide sensor 31, and water quality (especially pH) values ​​measured by the water quality measuring unit 33 is used as the input (Xn), and the BOD concentration of the raw water corresponding to the input value (Xn) is used as the output value (Yn). The pH value is preferably used as the water quality value. In addition to the volatile organic compound concentration, carbon dioxide concentration, and water quality values, the airflow measurement value obtained from the airflow meter 32 can also be used as the input (Xn) as needed. The control device 40 calculates the BOD concentration of the raw water by applying the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 and the water quality (especially pH) value measured by the water quality measuring unit 33 to the model, and controls the pump 23 based on the BOD concentration value. The control device 40 can also, as needed, apply the airflow value obtained from the airflow meter 32 to the model to calculate the BOD concentration of the raw water, in addition to the carbon dioxide concentration and water quality values. Then, when controlling the pump 23 based on the BOD concentration value, the control device 40 controls the pump 23 to increase the amount of nutrients added when the volatile organic compound concentration measured by the VOC sensor 30 increases, and controls the pump 23 to reduce the amount of nutrients added when the increasing volatile organic compound concentration decreases.

[0041] As is well known, in water, the form of inorganic carbonic acid changes according to pH, becoming free carbonic acid (CO2) and 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 reaction tank 10 may vary depending on the pH. Figure 3 In the wastewater treatment apparatus shown, the amount of nutrients added is controlled by taking into account the pH of the water in the reaction tank 10. Therefore, the amount of nutrients added can be optimized regardless of the pH of the raw water. Furthermore, 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 are water temperature fluctuations in the reaction tank 10, the water quality measuring unit 33 measures the water temperature in addition to the pH. In addition to the concentration of volatile organic compounds, carbon dioxide concentration, and pH, the amount of nutrients added can also be controlled based on the water temperature.

[0042] In wastewater treatment, multiple biological treatment reactors are sometimes connected in series. The treated water discharged from the upstream reactor is introduced into the downstream reactor. Through biological treatment in each reactor, highly purified water with organic matter removed is obtained. Figure 4 Is with Figure 1 , Figure 2 The illustrated device is a wastewater treatment apparatus that performs wastewater treatment based on aerobic treatment. It shows a wastewater treatment apparatus in which multiple reaction tanks 10 are arranged in series, i.e., in multiple stages. When the reaction tanks 10 are arranged in two or more stages, in the first-stage reaction tank 10, the concentration of volatile organic compounds, etc., in the gas released from that reaction tank is measured. Based on the measured values, the BOD concentration of the raw water is calculated, and based on this BOD concentration, the amount of nutrients added to the raw water supplied to that reaction tank can be controlled. Therefore, in Figure 4 In the wastewater treatment device shown, the VOC sensor 30, carbon dioxide concentration sensor 31, and airflow meter 32 are only installed in the first-stage reaction tank 10. Nutrient solution from the nutrient storage tank 21 is added to the raw water in the inlet pipe 13 connected to the first-stage reaction tank 10. The control device 40 calculates the BOD concentration of the raw water based on the measurements from the carbon dioxide concentration sensor 31 and the airflow meter 32, and controls the pump 23 that delivers the nutrient solution based on the BOD concentration. Furthermore, the control device 40 controls the amount of additional nutrients added based on the measurements from the VOC sensor 30, similar to the second or third embodiment.

[0043] When two or more reaction tanks 10 are connected in series, since most of the organic matter is decomposed and removed in the first-stage reaction tank 10, less organic matter needs to be removed in the reaction tanks 10 after the second stage. Furthermore, the microorganisms that proliferate in the first-stage reaction tank 10 die and decompose, thereby allowing nutrients to dissolve again. For these reasons, biological treatment can be carried out in the reaction tanks 10 after the second stage without adding nutrients back into the water supplied to them, maintaining the overall treatment performance of the wastewater treatment device. Therefore, it is not necessary to measure the concentration of volatile organic compounds, carbon dioxide concentration, and airflow in the reaction tanks after the second stage.

[0044] Example Next, the invention will be further described in detail through examples.

[0045] Test conditions First, the common test conditions for each embodiment will be described. A 19L volume container with a top cover was used. Figure 1The primary reactor shown is used for biological treatment based on aerobic treatment of raw water, which is organic wastewater. Aerobic microorganisms are carried on a sponge carrier made of hydrophobic polyurethane resin, and this sponge carrier is filled into the reactor at 30% of its bulk volume relative to the reactor volume. The retention time in the reactor is set to 8 hours. The raw water used is isopropanol-containing wastewater, simulating organic wastewater discharged from a semiconductor manufacturing plant. The BOD concentration in the raw water is approximately 900 mg / L, the nitrogen (N) concentration is less than 2 mg / L, and the phosphorus (P) concentration is less than 0.1 mg / L. The BOD volumetric loading rate during biological treatment is approximately 2.8 kg / m³. 3 The water temperature is approximately 20°C per day, the dissolved oxygen (DO) concentration in the reaction tank is above 2 mg / L, and the pH of the water in the reaction tank is 7.0~7.5. Air is supplied to the reaction tank at a flow rate of 10 L / min for ventilation.

[0046] Nitrogen (N), phosphorus (P), and trace metals were added to the raw water as nutrients. The concentration of volatile organic compounds (VOCs) in the gas released from the water in reaction tank 10 was measured as the amounts of nitrogen and phosphorus added were varied. Since acetone is produced as an intermediate metabolite in the biological treatment of isopropanol, the concentrations of isopropanol and acetone were measured in the VOC concentration determination. Under all conditions, the isopropanol concentration was below 10 ppm, almost undetectable. Under these conditions, it was assumed that when the reaction tank 10 reached a stable state, the dissolved phosphorus in the water within the reaction tank 10 was in the form of phosphoric acid.

[0047] Example 1 Phosphorus was added to make its concentration 10.6 mg / L relative to the volume of the raw water in the reaction tank 10 for biological treatment. The acetone concentration in the gas released from the water in the reaction tank 10 was 10 ppm. When the reaction tank 10 reached a stable state, the phosphoric acid concentration in the water in the reaction tank 10, i.e. the treated water, was measured. The result, converted from phosphoric acid, was 2.5 mg / L.

[0048] Example 2 Phosphorus was added to achieve a concentration of 3.4 mg / L relative to the volume of the raw water in reaction tank 10 for biological treatment. As a result, the concentration of acetone in the gas released from the water in reaction tank 10 was 50 ppm, and the phosphoric acid concentration of the treated water under stable conditions was 0.02 mg / L (calculated as phosphorus).

[0049] Example 3 Phosphorus was added to achieve a concentration of 4.5 mg / L relative to the volume of raw water in reaction tank 10 for biological treatment. The resulting acetone concentration in the gas released from the water in reaction tank 10 was 10 ppm. The phosphoric acid concentration in the treated water under steady-state conditions was measured and found to be 0.02 mg / L (as phosphorus). In Example 3, no excessive phosphorus addition was performed, which maintained a low concentration of volatile organic compounds in the gas released from the water in reaction tank 10 and reduced the concentration of dissolved phosphorus in the treated water. Table 1 summarizes the relationship between the phosphorus concentration added to the raw water and the acetone concentration measured as a volatile organic compound in Examples 1-3.

[0050] (Table 1)

[0051] In the biological treatment of isopropanol, acetone is generated as an intermediate metabolite. However, as the above results show, when the biological treatment is incomplete or poorly performed, acetone accumulates in the reaction tank 10, which can be detected as an increase in the concentration of acetone in the gas phase. If the concentration of phosphorus is increased, the concentration of acetone also decreases. Therefore, by measuring the concentration of volatile organic compounds such as acetone released from the water in the reaction tank 10, and increasing the amount of nitrogen and phosphorus added when the concentration tends to increase, and decreasing the amount added when the concentration tends to decrease, it can be concluded that the addition amount can be controlled to the minimum required for nutrients, that is, the addition amount can be optimized.

[0052] Symbol Explanation 10 Reaction Tanks 11. Carrier 12. Gas dissipation device 13 Inlet piping 14 Gas piping 15. Blower 16 covers 21 Nutrient storage tank 22 Nutrient solution piping 23 pumps 30 VOC sensor 31 Carbon dioxide concentration sensor 32. Air volume meter 33 Water Quality Testing Department 40. Control device.

Claims

1. A wastewater treatment method, comprising biologically treating raw water, which is organic wastewater, in a reaction tank, wherein the wastewater treatment method comprises: The concentration determination process includes, at least, determining the concentration of volatile organic compounds in the gas released from the water in the reaction tank; and The control process controls the amount of nutrients added to the raw water based on the concentration values ​​obtained in the concentration determination process. The volatile organic compounds whose concentration is measured in the concentration determination process are at least one of the volatile organic compounds contained in the raw water and the volatile organic compounds generated as intermediate metabolites in the biological treatment.

2. The drainage treatment method according to claim 1, wherein, In the concentration measurement process, in addition to measuring the concentration of volatile organic compounds, the concentration of carbon dioxide in the gas released from the water in the reaction tank is also measured.

3. The drainage treatment method according to claim 1 or 2, wherein, The wastewater treatment method further includes 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 process, in addition to using the concentration measurement value obtained in the concentration measurement process, the flow measurement value obtained in the flow measurement process is also used to control the amount of nutrients added to the raw water.

4. The drainage treatment method according to claim 1 or 2, wherein, In the biological treatment, the concentration of soluble phosphorus in the reaction tank is maintained below 0.5 mg / L.

5. The drainage treatment method according to claim 1 or 2, wherein, In the case of multiple reaction tanks connected in series, the concentration measurement process is performed on the first-stage reaction tank. In the control process, the amount of nutrients added to the raw water supplied to the first-stage reaction tank or the amount of nutrients added to the raw water in the first-stage reaction tank is controlled.

6. A drainage treatment device, comprising: The reaction tank is used for the biological treatment of raw water that is used as organic wastewater. An additive unit that adds nutrients to the raw water; A concentration measuring unit, which at least measures the concentration of volatile organic compounds in the gas released from the water in the reaction tank; as well as The control unit controls the amount of nutrient added by the addition unit based on the concentration measurement value obtained by the concentration measurement unit. The volatile organic compounds whose concentrations are measured by the concentration measuring unit are at least one of the volatile organic compounds contained in the raw water and the volatile organic compounds generated as intermediate metabolites in the biological treatment.

7. The drainage treatment device according to claim 6, wherein, In addition to measuring the concentration of volatile organic compounds, the concentration measuring unit also measures the concentration of carbon dioxide in the gas released from the water in the reaction tank.

8. The wastewater treatment apparatus according to claim 6 or 7, wherein, The control unit controls the reaction tank to maintain the concentration of soluble phosphorus below 0.5 mg / L.

9. The drainage treatment apparatus according to claim 6 or 7, wherein, Multiple of the aforementioned reaction tanks are connected in series. The addition unit adds the nutrients to the raw water supplied to the first-stage reaction tank or to the raw water already in the first-stage reaction tank, and The concentration measurement unit is provided for the first stage reaction tank.

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