Wastewater treatment method and wastewater treatment device

Abstract

To stably perform determination of an optimum addition amount of nutrient substances (for example, nitrogen, phosphorus, trace metals, etc.) to raw water which is organic waste water in biological treatment of the organic waste water.SOLUTION: A waste water treatment system has: a reaction tank 10 for biologically treating raw water which is organic waste water; addition means for adding nutrient substances to the raw water; a carbon dioxide concentration sensor 31 for measuring a concentration of carbon dioxide in a gas released from water in the reaction tank 10; an airflow meter 32 for measuring a flow rate of a gas supplied to the reaction tank 10 or the gas released from the reaction tank 10; and a controller 40 for controlling an addition amount of nutrient substances by the addition means based on a concentration value obtained by the carbon dioxide concentration sensor 31 and a flow rate value obtained by the airflow meter 32.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 which can stably determine the optimum amount of nutrients to be 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, comprising: carbon dioxide a first measuring step for measuring the concentration of the gas; a second measuring step for measuring the flow rate of the gas supplied to the reaction vessel or the gas discharged from the reaction vessel; and a measurement value of the concentration obtained in the first measuring step. and The flow rate measurement value obtained in the measurement step 2 A calculation step of calculating the organic matter concentration of the raw water from the organic matter concentration and a control step of controlling the amount of nutrients added to the raw water based on the amount of nutrients added.

[0008] The wastewater treatment device of the present invention comprises a reaction tank for biologically treating raw water, which is organic wastewater, a means for adding nutrients to the raw water, and a means for detecting the amount of nutrients in the gas released from the water in the reaction tank. carbon dioxide a first measuring means for measuring the concentration of the gas; a second measuring means for measuring the flow rate of the gas supplied to the reaction vessel or the gas discharged from the reaction vessel; a measurement value of the concentration obtained by the first measuring means; and a measurement value of the flow rate obtained by the second measuring means. The organic matter concentration in the raw water is calculated from the and a control means for controlling the amount of the nutrient substance added by the adding means based on the amount of the nutrient substance added. Effect of the Invention

[0009] According to the present invention, in the biological treatment of organic wastewater, it becomes possible to stably determine the optimum amount of nutrients to be 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 still 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 from public sewerage systems, 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 discharged 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] In the wastewater treatment method according to the present invention, in order to optimize the amount of nutrients added to the raw water, the BOD or TOC concentration of the raw water is not directly measured, but the concentration of a specific gas in the gas released from the water in the reaction tank and the flow rate of the gas supplied to the reaction tank or released from the reaction tank are measured. Then, the amount of nutrients added to the raw water is controlled based on the measured value of the concentration of the specific gas and the measured value of the flow rate of the gas. At this time, the organic matter concentration of the raw water may be calculated from the measured value of the concentration and the measured value of the flow rate, and the amount of nutrients added to the raw water may be controlled based on the calculated organic matter concentration, or 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 (e.g., pH) of the water in the reaction tank may be measured, and the amount of nutrients added to the raw water may be controlled based on the measured value of the concentration of the specific gas, the measured value of the flow rate, and the measured value of the water quality.

[0014] If the biological treatment is aerobic treatment, the concentration of the specific gas is measured, for example, as the concentration of carbon dioxide generated from the water in the reaction tank. In aerobic treatment, aeration or aeration is usually performed on the water in the reaction tank by blowing air into the reaction tank using a blower for blowing air, so the flow rate of the gas may be measured by measuring the flow rate of air supplied to the reaction tank from the blower for blowing air, or the total flow rate of the gas discharged from the reaction tank. When aerobic treatment is performed using a fluidized bed, a screen is placed in the reaction tank to separate the carrier, and air is also blown in to wash the screen. In this case, the total air volume of the blower for blowing air and the air volume for washing the screen may be used as the flow rate of the gas. If the biological treatment is anaerobic treatment, the concentration of the specific gas is measured, for example, as the concentration of methane generated from the water in the reaction tank, and since aeration is not usually performed in anaerobic treatment, the total flow rate of the gas discharged from the reaction tank may be measured as the flow rate of the gas.

[0015] 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.

[0016] 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.

[0017] 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 flow rate of air supplied to the reaction tank 10 for aeration. 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 the gas pipe 14 is provided with an air flow meter 32 for measuring the flow rate of air flowing therethrough at a position between the blower 15 and the aeration device 12. 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 of 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 should 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.

[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 flow rate (i.e., air volume) of air supplied to the reaction tank 10 for aeration are measured. Then, the BOD value of the raw water is calculated from the measured carbon dioxide concentration and the measured air flow rate, and the amount of nutrients added is determined based on the calculated BOD value. To achieve this, in this embodiment, a combination of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 and the measured air volume obtained by the air volume meter 32 is set as an input value (Xn), 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 input values ​​and output values ​​(for example, several tens to a hundred sets) are acquired in advance, and then a model (or a relational expression) is created. At this time, instead of using the combination of the carbon dioxide concentration and the measured air volume as the input value (Xn), the value obtained by multiplying the measured carbon dioxide concentration and the measured air volume (i.e., the multiplied value) may be used as the input value (Xn).

[0019] Once the model is created, a combination of the measured carbon dioxide concentration by the carbon dioxide concentration sensor 31 and the measured air volume 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 to be added 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 measured air volume by the air volume meter 32 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. Although the BOD concentration is used to create the model, the created model itself can be considered to directly output the amount of nutrients to be added by inputting the measured carbon dioxide concentration and the measured air volume. Therefore, once the model is created, the optimal amount of nutrients to be added can be determined without explicitly calculating the BOD concentration value from the measured carbon dioxide concentration and the measured air volume.

[0020] 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 an 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. 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., and the air volume supplied to the reaction tank 10 for aeration also varies depending on the configuration and size of the reaction tank 10, etc., so 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 air volume may vary depending on the type or source of the raw water, a model may be prepared for each type or source of 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.

[0021] In the wastewater treatment device shown in FIG. 1, an air flow meter 32 is provided in the gas pipe 14 to measure the flow rate of air supplied to the reaction tank 10, i.e., the air volume, through the gas pipe 14. However, instead of measuring the flow rate of air supplied to the reaction tank 10, the flow rate of gas discharged from the reaction tank 10 may be measured. When measuring the flow rate of gas discharged from the reaction tank 10, when the reaction tank 10 is completely covered with the lid 16, the air flow meter 32 may be installed in a pipe communicating with the inside of the reaction tank 10 to discharge the gas to the outside. When the reaction tank 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 tank 10 can be made as small as possible, and a cylindrical pipe or the like can be inserted below the water surface, and the air flow meter 32 can be installed in the pipe.

[0022] In order to control the amount of nutrients added to the raw water, it is possible to measure the organic matter concentration in the raw water online using an online TOC concentration meter. However, the online TOC concentration meter has a thin pipe for drawing a small amount of sample water into the measurement device, which is prone to clogging and unstable measurement values. In contrast, the carbon dioxide concentration sensor 31 performs measurement without contacting the water, so the measurement values ​​are very stable. 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 determine the optimal amount of nutrients to be added to the raw water without directly measuring the organic matter concentration in the raw water.

[0023] FIG. 2 shows a wastewater treatment device according to another embodiment of the present invention. The wastewater treatment device shown in FIG. 2 is the wastewater treatment device shown in FIG. 1, in which a water quality measurement unit 33 for measuring the water quality in the reaction tank 10 is provided, and the measurement results in the water quality measurement unit 33 are also sent to the control device 40. The water quality items measured by the water quality measurement unit 33 include at least pH, and other than pH, water temperature, etc. may be measured. The model used in the wastewater treatment device of this embodiment is an input (Xn) of a combination of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31, the measured air volume obtained by the air volume meter 32, and the measured water quality (particularly pH) measured by the water quality measurement unit 33, and the BOD concentration of the raw water corresponding to the input value (Xn) is an output value (Yn), and is created in the same manner as described above. The control device 40 applies the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31, the measured air volume obtained by the air volume meter 32, and the measured water quality (particularly pH) measured by the water quality measurement 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.

[0024] As is well known, inorganic carbonic acid in water is converted into CO2, HCO3, etc. depending on the pH. - , CO3 2- The form of the nutrient changes depending on the pH. Therefore, even if the organic matter concentration in the raw water is the same, the carbon dioxide concentration in the gas released from the water in the reaction tank 10 may change depending on the pH. In the wastewater treatment device shown in FIG. 2, the amount of nutrients added is controlled taking into account the pH of the water in the reaction tank 10, so that the amount of nutrients added can be optimized regardless of the pH of the raw water. The solubility of carbon dioxide in water depends on the water temperature, and if the solubility of carbon dioxide changes, the carbon dioxide concentration in the gas released from the water in the reaction tank 10 also changes. Therefore, when the water temperature in the reaction tank 10 fluctuates, the water quality measurement unit 33 measures the water temperature in addition to the pH, and the amount of nutrients added can be controlled based on the water temperature in addition to the carbon dioxide concentration, air volume, and pH.

[0025] In wastewater treatment, a plurality of reaction tanks for biological treatment are connected in series, and treated water discharged from the reaction tank in the first stage is led to the reaction tank in the next stage, and biological treatment is performed in each reaction tank to obtain treated water from which organic matter has been highly removed. FIG. 3 shows a wastewater treatment device for performing wastewater treatment by aerobic treatment similar to that shown in FIG. 1 and FIG. 2, 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 two or more stages, the carbon dioxide concentration in the gas discharged from the reaction tank in the first stage 10 is measured, and the air volume supplied to the reaction tank is measured, and the BOD concentration value of the raw water is calculated from the carbon dioxide concentration and the air volume, and the amount of nutrients added to the raw water supplied to the reaction tank can be controlled based on the BOD concentration value. In this case, the pH of the water in the reaction tank 10 in the first stage can also be measured, and the amount of nutrients added to the raw water can be controlled based on the carbon dioxide concentration, the air volume, and the pH. 3, the carbon dioxide concentration sensor 31, the air flow meter 32, 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, the air flow meter 32, and the water quality measurement unit 33, and controls the pump 23 that supplies the nutrient liquid based on the BOD concentration value.

[0026] 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 organic matter to 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 disintegrate, 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 device can be maintained. For this reason, it is not necessary to measure the carbon dioxide concentration, air volume, and pH in the second and subsequent reaction tanks. EXAMPLES

[0027] Next, the present invention will be described in more detail with reference to examples and comparative examples.

[0028] [Test conditions] First, the test conditions common to Examples 1 to 4 and Comparative Examples 1 and 2 will be described. A single-stage reaction tank with a volume of 19 L as shown in FIG. 2 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 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. Air was supplied to the reaction tank at a flow rate of 3 to 5 L / min for aeration.

[0029] 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 and the pH 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.

[0030] [Comparative Example 1] The BOD concentration of the raw water 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 0.39.

[0031] [Example 1] The BOD concentration of the raw water was calculated from the carbon dioxide concentration and air volume, and the coefficient of determination R was calculated by multiple regression analysis for the carbon dioxide concentration, air volume, and each BOD concentration. 2 The calculated value was 0.82. It was found that the accuracy of calculating the BOD concentration was significantly improved by using the carbon dioxide concentration and air volume compared to when only the carbon dioxide concentration was used.

[0032] [Example 2] The BOD concentration of the raw water was calculated from the carbon dioxide concentration and air volume. The measured carbon dioxide concentration was multiplied by the measured air volume, and the coefficient of determination R was calculated by performing a simple regression analysis on this multiplication and each BOD concentration. 2 The calculated value was 0.83. It was found that the accuracy of calculating the BOD concentration could be further improved by using the product of the carbon dioxide concentration and the air volume.

[0033] [Comparative Example 2] The BOD concentration of the raw water was calculated from the carbon dioxide concentration and pH, 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 0.40.

[0034] [Example 3] The BOD concentration of raw water was calculated from the carbon dioxide concentration, air volume, and pH. The coefficient of determination R was calculated by multiple regression analysis for the carbon dioxide concentration, air volume, pH, and each BOD concentration. 2 The calculated value was 0.89. It was found that the accuracy of the BOD concentration calculation was significantly improved by using the air volume in addition to the carbon dioxide concentration and pH, compared to when the carbon dioxide concentration and pH were used.

[0035] The BOD concentration of the raw water is calculated from the carbon dioxide concentration, air volume, and pH. The measured carbon dioxide concentration is multiplied by the measured air volume, and the coefficient of determination R is calculated by multiple regression analysis of this multiplication, pH, and each BOD concentration. 2The calculated value was 0.96. It was found that the accuracy of calculating the BOD concentration was significantly improved by multiplying the measured carbon dioxide concentration by the measured air volume and then using this multiplied value and the pH, compared to when carbon dioxide concentration and pH were used.

[0036] From the comparative examples and examples, it was found that the amount of nutrients added can be optimized by using at least the air volume 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]

[0037] 10 Reactor 11 Carriers 12 Air diffuser 13 Inlet piping 14 Gas piping 15 Blower 16 Lid 21 Nutrient storage tank 22 Nutrient solution piping 23 Pump 31 Carbon dioxide concentration sensor 32 Air flow meter 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 concentration of carbon dioxide in a gas released from the water in the reaction tank; a second measuring step of measuring a flow rate of the gas supplied to the reaction tank or the gas discharged from the reaction tank; a calculation step of calculating an organic matter concentration of the raw water from the measured concentration value obtained in the first measurement step and the measured flow rate value obtained in the second measurement step; A control step of controlling an amount of nutrients added to the raw water based on the organic matter concentration; The wastewater treatment method comprises the steps of:

2. 2. The wastewater treatment method according to claim 1, wherein in the calculation step, a value obtained by multiplying the measured concentration by the measured flow rate is used when calculating the organic matter concentration of the raw water.

3. A third measurement step of measuring the pH of the water in the reaction tank, 3. The wastewater treatment method according to claim 1, wherein in the calculation step, the organic matter concentration of the raw water is calculated using the measured pH value obtained in the third measurement step in addition to the measured concentration and the measured flow rate.

4. 3. 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 wastewater treatment method as described in claim 3, wherein, when a plurality of the reaction tanks are arranged in series, the first measurement process, the second measurement process, and the third measurement process are performed on a front-stage reaction tank, and the amount of nutrients added to the raw water supplied to the front-stage reaction tank or the raw water in the front-stage reaction tank is controlled in the control process.

6. A reaction tank for biologically treating raw water, which is organic wastewater; An adding means for adding nutrients to the raw water; A first measuring means for measuring a concentration of carbon dioxide in a gas released from the water in the reaction tank; A second measuring means for measuring a flow rate of a gas supplied to the reaction tank or a gas discharged from the reaction tank; a control means for calculating an organic matter concentration in the raw water from the measured concentration value obtained by the first measurement means and the measured flow rate value obtained by the second measurement means, and controlling the amount of the nutrient added by the adding means based on the organic matter concentration; A wastewater treatment device comprising:

7. The wastewater treatment device according to claim 6, wherein the control means uses a value obtained by multiplying the measured organic matter concentration by the measured flow rate when calculating the organic matter concentration.

8. a third measuring means for measuring a pH of the water in the reaction tank; The wastewater treatment device according to claim 6 or 7, wherein the control means calculates the organic matter concentration using the measured pH value obtained by the third measurement means in addition to the measured concentration and the measured flow rate.

9. 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, 8. The wastewater treatment device according to claim 6, wherein the first measuring means and the second measuring means are provided for the reaction tank in the forefront stage.

10. 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, 9. The wastewater treatment device according to claim 8, wherein the first measurement means, the second measurement means and the third measurement means are provided for the reaction tank in the forefront stage.

Images