Wastewater treatment method and wastewater treatment device

Abstract

To optimize an amount of nutrients (nitrogen, phosphorus, trace metals or the like as an example) added to raw water being organic wastewater, in biological treatment of the organic wastewater.SOLUTION: A wastewater treatment device includes: a reaction tank 10 for biologically treating raw water; adding means for adding nutrient substances to the raw water (for example, a nutrient substance storage tank 21 and a pump 23); a carbon dioxide concentration sensor 31 for measuring a carbon dioxide concentration in a gas released from the reaction tank 10; a water quality measuring unit 33 for acquiring one or more measured values (for example, pH value) regarding a water quality of water in the reaction tank 10; and a control device 40. Based on a carbon dioxide concentration value obtained by the carbon dioxide concentration sensor 31 and a measured value obtained by the water quality measuring unit 33, the control device 40 controls an amount of nutrient added by the adding means.SELECTED DRAWING: Figure 1

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 technology]

[0002] Biological treatment using microorganisms is commonly used to treat wastewater containing organic matter, i.e., organic wastewater, before it is released into the environment. In biological treatment, in order to maintain high activity of the microorganisms in decomposing organic matter, it is necessary to optimize environmental conditions such as water temperature and pH, as well as add nutrients such as nitrogen, phosphorus, and trace metals. Compared to wastewater in public sewerage systems into which domestic wastewater flows, wastewater from factories is more likely to be deficient in nutrients. In particular, wastewater from chemical plants and semiconductor manufacturing plants is significantly deficient in the nutrients required for biological treatment.

[0003] It is recommended that the amount of nutrients added to raw water, which is organic wastewater, be proportional to the organic matter concentration in the raw water. Assuming that the organic matter concentration in the raw water is expressed as biochemical oxygen demand (BOD), the preferred amounts of nitrogen (N) and phosphorus (P) added as nutrients in wastewater treatment by aerobic microorganisms, i.e., aerobic treatment, are, for example, BOD:N:P=100:5:1 by mass. It is difficult to measure the BOD of raw water online or in a short time, but the total organic carbon (TOC) concentration in water can be measured online. Therefore, the correlation between the TOC concentration and BOD in the raw water is obtained in advance, the TOC concentration of the raw water is monitored using an online TOC concentration meter, and converted into a BOD value, and the amount of nitrogen and phosphorus added is controlled based on the obtained BOD value (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-334285 A Summary of the Invention [Problem to be solved by the invention]

[0005] The method of controlling the amount of nutrients added based on the TOC concentration measured online has the problem that the inside of the piping of the online TOC concentration meter can become clogged due to the accumulation of suspended solids (SS) and oil, and the formation of biofilms, making the measurement unstable.

[0006] An object of the present invention is to provide a wastewater treatment method and wastewater treatment apparatus capable of optimizing the amount of nutrients added to raw water, which is organic wastewater, in the biological treatment of organic wastewater. [Means for solving the problem]

[0007] The wastewater treatment method of the present invention is a wastewater treatment method for biologically treating raw water, which is organic wastewater, in a reaction tank, the method including a first measurement step of measuring a carbon dioxide concentration in a gas released from the water in the reaction tank, a second measurement step of acquiring one or more measured values ​​related to the water quality of the water in the reaction tank, and, based on the measured value of the carbon dioxide concentration obtained in the first measurement step and the one or more measured values ​​obtained in the second measurement step, The microorganisms used in biological treatment need to maintain their decomposition properties and grow. Nutritional substances To raw water A control step for controlling the amount of addition. The one or more measurements of water quality are selected from pH, water temperature, dissolved oxygen concentration, oxidation-reduction potential, electrical conductivity, and turbidity, and do not include a pH measurement. do.

[0008] The wastewater treatment device of the present invention comprises a reaction tank for biologically treating raw water which is organic wastewater, The microorganisms used in biological treatment need to maintain their decomposition properties and grow. Nutrients In raw water The method includes: adding means for adding nutrients; a first measuring means having a first sensor for measuring the carbon dioxide concentration in the gas released from the water in the reaction tank; a second measuring means for acquiring one or more measured values ​​relating to the water quality in the reaction tank; and a control means for controlling the amount of nutrients added by the adding means based on the carbon dioxide concentration value obtained by the first measuring means and the one or more measured values ​​obtained by the second measuring means. The one or more measurements of water quality are selected from pH, water temperature, dissolved oxygen concentration, oxidation-reduction potential, electrical conductivity, and turbidity, and do not include a pH measurement. do. Effect of the Invention

[0009] According to the present invention, in the biological treatment of organic wastewater, it becomes possible to optimize the amount of nutrients added to raw water, which is organic wastewater. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram showing a wastewater treatment device according to an embodiment of the present invention; [Diagram 2] FIG. 13 is a diagram showing a wastewater treatment device according to another embodiment. [Diagram 3] FIG. 13 is a diagram showing a wastewater treatment device according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Next, an embodiment of the present invention will be described with reference to the drawings.

[0012] The present invention relates to a technology for performing biological treatment using microorganisms on raw water, which is organic wastewater, and decomposing and removing organic substances in the raw water. The organic wastewater targeted by the present invention is not particularly limited as long as it is applicable to biological treatment, and includes, for example, wastewater discharged in sewage treatment, wastewater discharged from various factories such as food factories, chemical factories, semiconductor manufacturing factories, liquid crystal manufacturing factories, and paper and pulp factories, and wastewater discharged from business establishments in other fields. Compared with wastewater from public sewerage systems, wastewater from private factories is likely to lack nutrients necessary to maintain high decomposition activity of the microorganisms used in biological treatment, and in particular, the lack of nutrients is remarkable in wastewater from chemical factories, semiconductor manufacturing factories, and liquid crystal manufacturing factories. When an external organic source such as methyl alcohol is added to inorganic nitrate wastewater (or inorganic nitrite wastewater) that does not contain organic matter and a denitrification treatment is performed, the wastewater to which an external organic source has been added is also an organic wastewater targeted by the present invention. The biological treatment in the present invention includes aerobic treatment, anaerobic treatment, denitrification treatment, etc., and these biological treatments are carried out by the activated sludge process, the membrane bioreactor (MBR) process, a biofilm process using a fluidized bed or a fixed bed, a granular process, etc.

[0013] FIG. 1 shows a wastewater treatment apparatus according to an embodiment of the present invention. The wastewater treatment apparatus shown in FIG. 1 includes a fluidized bed type reaction tank 10 that stores raw water, which is organic wastewater, and biologically treats the raw water under aerobic conditions. The reaction tank 10 is a biological treatment tank, and treated water from which organic matter has been decomposed and removed by biological treatment is discharged from the reaction tank 10. The reaction tank 10 is filled with carriers 11, and an aeration device 12 is provided at the bottom of the reaction tank 10 to blow air into the reaction tank 10 for supplying oxygen, i.e., for aeration. The reaction tank 10 is connected to an inlet pipe 13 that supplies raw water to the reaction tank 10. The aeration device 12 is connected to a gas pipe 14 for supplying air to the aeration device 12, and the gas pipe 14 is provided with a blower 15 for supplying air. Examples of the carrier 11 that can be used here include a plastic carrier, a sponge carrier, and a gel carrier, and among these, it is preferable to use a sponge carrier from the viewpoint of cost and durability. The reaction tank 10 may be provided with an agitation device that agitates the carrier 11.

[0014] In biological treatment, nutrients are necessary for microorganisms to maintain high decomposition activity and grow. When nutrients are insufficient in the raw water, nutrients must be added to the raw water in the reaction tank 10 or at a stage preceding the reaction tank 10. In the wastewater treatment device of this embodiment, a nutrient storage tank 21 for storing a solution of nutrients (i.e., nutrient liquid) is provided, and the nutrient storage tank 21 and the inlet pipe 13 are connected via a nutrient liquid pipe 22. The nutrient liquid pipe 22 is provided with a pump 23 for feeding the nutrient liquid. Therefore, in this wastewater treatment device, nutrients can be added to the raw water that flows through the inlet pipe 13 and is supplied to the reaction tank 10, and the amount of nutrients added to the raw water can be controlled by controlling the pump 23. Nutrients can be roughly divided into nutrient salts containing nitrogen and phosphorus, and trace elements that are required in smaller amounts than 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 the nitrogen source. As the phosphorus source, phosphoric acid or a phosphate can be used.

[0015] In the wastewater treatment device of this embodiment, the amount of nutrients added is controlled based on the carbon dioxide concentration in the gas released from the water in the reaction tank 10 by biological treatment and the raw water BOD concentration calculated from one or more measured values ​​related to the water quality in the reaction tank 10. For this purpose, the reaction tank 10 is provided with a carbon dioxide concentration sensor 31 for measuring the carbon dioxide concentration in the gas released from the water in the reaction tank 10 and a water quality measurement unit 33 for measuring the water quality for one or more items. Assuming that the reaction tank 10 is covered with a lid 16, the carbon dioxide concentration sensor 31 is installed in the gas phase part in the reaction tank 10 or in a pipe connected to this gas phase part. Since it is necessary to prevent condensation of the carbon dioxide concentration sensor 31, when the carbon dioxide concentration sensor 31 is installed in the pipe, the pipe may be kept warm and a mist separator may be installed immediately before the carbon dioxide concentration sensor 31. In addition, a desulfurization device for removing corrosive gases may be installed. When the reaction vessel 10 is an open system, in order to reduce the influence of outside air on the measurement results, the open part at the top of the reaction vessel 10 is made as small as possible, a cylindrical pipe or the like is inserted below the water surface, and the carbon dioxide concentration sensor 31 is disposed at a position above the water surface in the pipe. As the carbon dioxide concentration sensor 31, for example, an optical, electrochemical, or semiconductor type can be used, but it is particularly preferable to use a sensor using the non-dispersive infrared absorption method (NDIR). The carbon dioxide concentration can be measured manually or online.

[0016] The water quality in the reaction tank 10 is measured by the water quality measuring unit 33 as, for example, pH (hydrogen ion concentration index), water temperature, dissolved oxygen concentration (DO), oxidation-reduction potential (ORP), conductivity, turbidity, etc., and the water quality measuring unit 33 is configured to measure one or more of these items. As is well known, the form of inorganic carbon in water is CO2, HCO3, etc., depending on the pH. - , CO3 2-Since the pH value changes according to the water temperature, it is considered that the pH is particularly closely related to the carbon dioxide concentration in the gas released from the water in the reaction tank 10 by the biological treatment. Furthermore, since the solubility of carbon dioxide changes according to the water temperature, the water temperature is also closely related to the carbon dioxide concentration in the gas released from the water in the reaction tank 10. In this embodiment, the BOD of the raw water is not actually measured, but instead, a measured value including the concentration of carbon dioxide released by the biological treatment is used to control the amount of nutrients to be added. Therefore, it is preferable that the items measured by the water quality measurement unit 33 include pH and water temperature. The measurement in the water quality measurement unit 33 may be performed manually or online.

[0017] There are also online TOC concentration meters that measure the total organic carbon (TOC) concentration in water online, but these have thin piping to draw in a small amount of sample water into the measurement device, which can easily become clogged and can lead to unstable measurements. On the other hand, the carbon dioxide concentration sensor 31 performs measurements without coming into contact with the water, so the measurements are very stable. In addition, the water quality measurement unit 33 that measures pH, water temperature, etc. is a sensor that is immersed in the reaction tank 10, so the measurements are also very stable.

[0018] Next, the control of the amount of nutrients added in the wastewater treatment device shown in FIG. 1 will be described. It is recommended that the amount of nutrients (nutrient salts and trace metals) added to raw water should be proportional to the organic matter concentration in the raw water, preferably the BOD. For example, it is recommended that the amount of nitrogen (N) and phosphorus (P) added in aerobic treatment be BOD:N:P=100:5:1 on a mass basis. In this embodiment, the BOD of the raw water is not measured by an online TOC concentration meter or the like, but instead, the carbon dioxide concentration in the gas released from the water in the reaction tank 10 by biological treatment and the water quality in the reaction tank 10 are measured. Then, the BOD value of the raw water is calculated from the measured value of the carbon dioxide concentration and one or more measured values ​​related to the water quality, and the amount of nutrients added is determined based on the calculated BOD value. For this purpose, in this embodiment, a combination of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 and the measurement value obtained by the water quality measurement unit 33 is set as an input value (Xn), and the BOD concentration of the raw water corresponding to the input value (Xn) is set as an output value (Yn), and a certain number of combinations of the input value and the output value (for example, several tens to a hundred sets) are acquired in advance, and then a model (or a relational expression) is created. Once the model is created, the combination of the measurement value of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 and the measurement value obtained by the water quality measurement unit 33 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 addition of nutrients to the raw water and the amount of addition are controlled. In order to perform such control, the wastewater treatment device is provided with a control device 40 that holds the created model, applies the carbon dioxide concentration value obtained by the carbon dioxide concentration sensor 31 and the measurement value obtained by the water quality measurement unit 33 to the model to calculate the BOD concentration value of the raw water, and controls the start / stop and flow rate of the pump 23 based on the BOD concentration value.

[0019] Next, the creation of the model will be described. A model that outputs the BOD concentration of raw water corresponding to an input value as an output value when the input value is input can be created, for example, by using various regression analyses. In particular, when a model is created by supervised learning using a neural network technique, the accuracy of controlling the amount of added nutrients is improved. Since the carbon dioxide concentration obtained by the carbon dioxide concentration sensor 31 may vary depending on the configuration and size of the reaction tank 10, the size of the gas phase part in the reaction tank 10, the type of biological treatment, etc., a model may be set for each reaction tank 10. Furthermore, since the relationship between the BOD of the raw water and the measured carbon dioxide concentration and pH may vary depending on the type or source of the raw water, a model may be prepared for each type and source of the raw water, and a model to be used for controlling the amount of added nutrients may be selected from the models prepared in this way depending on the type and source of the raw water.

[0020] In the wastewater treatment device shown in FIG. 1, air is blown into the reaction tank 10, but the atmosphere usually contains about 400 ppm of carbon dioxide. When measuring the carbon dioxide concentration to estimate the amount of carbon dioxide generated by biological treatment, it is necessary to take into account the amount of carbon dioxide in the blown air from the beginning. When the variation in the amount of carbon dioxide in the blown air is small, the model created as described above already includes the contribution of the carbon dioxide contained in the blown air, so that the amount of nutrients to be added can be determined using the model without measuring the carbon dioxide concentration in the blown air. However, when the carbon dioxide concentration in the blown air varies, such as when air containing exhaust gas from a boiler in a factory is blown in, it is necessary to determine the amount of nutrients to be added by making a correction according to the carbon dioxide concentration in the gas blown into the reaction tank 10. FIG. 2 shows a wastewater treatment device that makes such a correction according to the carbon dioxide concentration blown into the reaction tank 10.

[0021] The wastewater treatment device shown in Fig. 2 is similar to the wastewater treatment device shown in Fig. 1, but differs from that shown in Fig. 1 in that a carbon dioxide concentration sensor 32 is provided at the outlet side of the blower 15 in the gas pipe 14 to measure the carbon dioxide concentration in the air being blown in. The measurement value of the carbon dioxide concentration sensor 32 provided in the gas pipe 14 is also sent to the control device 40. The control device 40 applies the difference between the measurements by the carbon dioxide concentration sensors 31 and 32 and the measurement value obtained by the water quality measurement unit 33 to a model to calculate the BOD concentration value of the raw water, and controls the pump 23 based on the BOD concentration value.

[0022] In wastewater treatment, a plurality of reaction tanks for biological treatment are connected in series, and treated water discharged from the previous reaction tank is led to the next reaction tank and biological treatment is performed in each reaction tank, thereby obtaining treated water from which organic matter has been highly removed. FIG. 3 shows a wastewater treatment device in which a plurality of reaction tanks 10 for biological treatment are arranged in series, i.e., in multiple stages. When the reaction tanks 10 are arranged in two or more stages, it is preferable to measure the carbon dioxide concentration in the gas discharged from the reaction tank in the first stage and obtain one or more measured values ​​related to the water quality in the reaction tank 10 to calculate the BOD concentration value of the raw water, and to control the amount of nutrients added to the raw water supplied to the first stage reaction tank 10 based on the BOD concentration value. Therefore, in the wastewater treatment device shown in FIG. 3, the carbon dioxide concentration sensor 31 and the water quality measurement unit 33 are provided only in the first stage reaction tank 10, and the nutrient liquid 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 value of the raw water from the measurements of the carbon dioxide concentration sensor 31 and the water quality measurement unit 33, and controls the pump 23 that feeds the nutrient solution based on the BOD concentration value.

[0023] When two or more reaction tanks 10 are provided in series, most of the organic matter is decomposed and removed in the first reaction tank 10, so that the amount of organic matter that must be removed in the second and subsequent reaction tanks 10 is reduced. In addition, the microorganisms that have proliferated in the first reaction tank 10 die and break down, causing the nutrients to be re-eluted. For these reasons, it is possible to proceed with biological treatment in the second and subsequent reaction tanks 10 without adding nutrients to the water supplied to the second and subsequent reaction tanks 10, and the overall treatment performance of the wastewater treatment equipment can be maintained. EXAMPLES

[0024] Next, the present invention will be described in more detail with reference to examples and comparative examples.

[0025] [Test condition 1] First, the test conditions common to Examples 1 to 3 and Comparative Examples 1 and 2 will be described. A single-stage reaction tank with a volume of 19 L was used to carry out aerobic biological treatment of raw water, which was organic wastewater. Aerobic microorganisms were supported on a sponge carrier made of hydrophobic polyurethane resin, and such sponge carriers were filled in the reaction tank at a bulk volume of 20% of the volume of the reaction tank. The retention time in the reaction tank was 18 hours. Wastewater containing isopropyl alcohol was used as the raw water. The BOD concentration in the raw water was about 900 mg / L (standard concentration), the nitrogen (N) concentration in the raw water was 2 mg / L or less, and the phosphorus (P) concentration was 0.1 mg or less. The BOD volume load during biological treatment was about 1 kg / m 3 / day, the water temperature was about 20°C, the dissolved oxygen concentration (DO) of the water in the reaction tank was 2 mg / L or more, and the pH of the water in the reaction tank was 6.0 to 7.5.

[0026] Sufficient nutrients (nitrogen (N) and phosphorus (P)) were added to the raw water so that the BOD:N:P ratio was 100:5:1, and the concentration of carbon dioxide released from the water in the reaction tank, as well as the pH and dissolved oxygen (DO) concentrations of the water in the reaction tank were monitored. This type of monitoring was repeated while intentionally changing the BOD concentration in the raw water from the standard concentration of 100% to 30% and 60%. Note that being able to calculate the BOD concentration of the raw water with high accuracy is the same as having high accuracy in nutrient addition control.

[0027] [Comparative Example 1] The BOD concentration was calculated from the carbon dioxide concentration, and the coefficient of determination R was calculated by simple regression analysis for the carbon dioxide concentration and each BOD concentration. 2 The calculated value was 0.840.

[0028] [Example 1] The BOD concentration was calculated from the carbon dioxide concentration and the pH of the water in the reaction tank, and the coefficient of determination R was calculated by multiple regression analysis for the carbon dioxide concentration, pH, and each BOD concentration. 2 The calculated value was 0.991. It was found that the accuracy of calculating the BOD concentration was significantly improved by using the carbon dioxide concentration and pH compared to using only the carbon dioxide concentration.

[0029] [Example 2] The BOD concentration was calculated from the carbon dioxide concentration and the pH of the water in the reaction tank, and the coefficient of determination R was calculated for the carbon dioxide concentration, pH, and each BOD concentration by neural network analysis. 2 The calculated value was 0.996. It was found that the calculation accuracy could be further improved by using a neural network model.

[0030] [Error variance in neural network analysis] According to the above-mentioned test conditions, the carbon dioxide concentration, pH and dissolved oxygen concentration were monitored. Therefore, multiple data sets were obtained with the carbon dioxide concentration, pH and dissolved oxygen concentration as inputs and the BOD concentration as output. A specific data set was used as test data for all the obtained data sets, and the other data sets were used as training data to create a model from the training data by neural network analysis, and the error between the output value when the test data was input to the model and the actual measured value of the BOD of the raw water was calculated. This operation was repeated for all the data sets as cross-validation, and the variance of the obtained error was calculated and evaluated. Note that the lower the error variance value, the more appropriately the BOD concentration of the raw water was calculated.

[0031] [Comparative Example 2] The error variance for a data set using only carbon dioxide concentration as input was found to be 290.

[0032] [Example 3] The error variance for the data set with carbon dioxide and dissolved oxygen as inputs improved to 61. The error variance for the data set with carbon dioxide and pH as inputs was 11. The error variance for the data set with carbon dioxide, pH, and dissolved oxygen as inputs was 22.

[0033] [Test condition 2] Test condition 2 is a test condition common to Examples 4 and 5 and Comparative Example 3. In contrast to test condition 1, the sponge carrier was filled in the reaction tank to a bulk volume of 30% of the volume of the reaction tank, the retention time in the reaction tank was 8 hours, and the water temperature was varied from 20 to 30°C. The BOD volume load during biological treatment was approximately 3 kg / m 3 / day, and the pH of the water in the reaction tank was 5.6 to 7.8. The concentration of carbon dioxide released from the water in the reaction tank, as well as the pH and temperature of the water in the reaction tank were monitored.

[0034] [Comparative Example 3] The BOD concentration was calculated from the carbon dioxide concentration, and the coefficient of determination R was calculated by simple regression analysis for the carbon dioxide concentration and each BOD concentration. 2 The calculated value was 0.770.

[0035] [Example 4] The BOD was calculated from the carbon dioxide concentration and the water temperature in the reaction tank, and the coefficient of determination R was calculated for the carbon dioxide concentration, water temperature, and each BOD concentration by neural network analysis. 2 The calculated value was 0.927. It was found that the accuracy of calculating the BOD concentration was significantly improved by using the carbon dioxide concentration and water temperature compared to when only the carbon dioxide concentration was used.

[0036] [Example 5] The BOD was calculated from the carbon dioxide concentration, water temperature, and pH in the reaction tank. The coefficient of determination R was calculated by neural network analysis for the carbon dioxide concentration, water temperature, pH, and each BOD concentration. 2 The calculated value was 0.926. It was found that the accuracy of calculating the BOD concentration was significantly improved by using the carbon dioxide concentration, water temperature, and pH compared to when only the carbon dioxide concentration was used.

[0037] From the comparative examples and examples, it was found that the amount of nutrients added can be optimized by using one or more measured values ​​of the water quality in the reaction tank in addition to the carbon dioxide concentration and calculating the BOD concentration of the raw water using a model created in advance. [Explanation of symbols]

[0038] 10 Reactor 11 Carrier 12 Air diffuser 13 Inlet piping 14 Gas piping 15 Blower 16 Lid 21 Nutrient storage tank 22 Nutrient solution piping 23 Pump 31,32 Carbon dioxide concentration sensor 33 Water quality measurement section 40 Control device

Claims

1. A wastewater treatment method for biologically treating raw water, which is organic wastewater, in a reaction tank, comprising: a first measuring step of measuring a carbon dioxide concentration in a gas released from the water in the reaction tank; a second measuring step of obtaining one or more measurements related to the water quality in the reaction tank; a control step of controlling an amount of nutrients required for the microorganisms used in the biological treatment to maintain the decomposition properties of the microorganisms and grow, based on the measured value of the carbon dioxide concentration obtained in the first measurement step and the one or more measured values ​​obtained in the second measurement step, to be added to the raw water; having The one or more measured values ​​relating to water quality are one or more measured values ​​selected from pH, water temperature, dissolved oxygen concentration, oxidation-reduction potential, electrical conductivity and turbidity, and include a measured value of pH.

2. A calculation step of calculating an organic matter concentration of raw water from the measured value of the carbon dioxide concentration obtained in the first measurement step and the one or more measured values ​​obtained in the second measurement step, 2. The wastewater treatment method according to claim 1, wherein the control step is a step of controlling an amount of nutrients added to the raw water based on the organic matter concentration.

3. The wastewater treatment method according to claim 1 or 2, wherein the measured values ​​obtained in the second measuring step include a measured value of water temperature.

4. 4. The wastewater treatment method according to claim 1, wherein, when a plurality of the reaction tanks are provided in series, the first measurement step and the second measurement step are performed for a first-stage reaction tank, and an amount of nutrients added to the raw water supplied to the first-stage reaction tank or the raw water in the first-stage reaction tank is controlled in the control step.

5. A reaction tank for biologically treating raw water, which is organic wastewater; An addition means for adding nutrients necessary for the microorganisms used in the biological treatment to maintain the decomposition properties of the microorganisms and grow to the raw water; a first measuring means having a first sensor for measuring a carbon dioxide concentration in a gas released from the water in the reaction tank; A second measuring means for obtaining one or more measurements related to the water quality in the reaction tank; A control means for controlling the amount of the nutrient added by the adding means based on the carbon dioxide concentration value obtained by the first measuring means and the one or more measured values ​​obtained by the second measuring means; having The one or more measured values ​​relating to water quality are one or more measured values ​​selected from pH, water temperature, dissolved oxygen concentration, oxidation-reduction potential, conductivity and turbidity, and include a measured value of pH.

6. 6. The wastewater treatment device according to claim 5, wherein the control means calculates an organic matter concentration in the raw water from the measured value of the carbon dioxide concentration obtained by the first measurement means and the one or more measured values ​​obtained by the second measurement means, and controls the amount of the nutrients to be added based on the organic matter concentration.

7. The wastewater treatment device according to claim 5 or 6, wherein the measured values ​​acquired by the second measuring means include a measured value of water temperature.

8. A plurality of the reaction vessels are provided in series, The adding means adds nutrients to the raw water supplied to the first stage reaction tank or to the raw water in the first stage reaction tank, The wastewater treatment device according to claim 5 , wherein the first measuring means and the second measuring means are provided for the reaction tank in the forefront stage.

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