Wastewater treatment method and wastewater treatment device

Abstract

A wastewater treatment device is provided with: a reaction tank (10) for performing aerobic biological treatment on organic wastewater containing at least one of a sulfur compound and a nitrogen compound; a removal means (52) for removing corrosive gas from the gas discharged from the water in the reaction tank; a measurement means (31) for measuring the concentration of carbon dioxide contained in the gas from which the corrosive gas has been removed; and a control means (40) for controlling the aerobic biological treatment on the basis of the carbon dioxide concentration measured by the measurement means.

Description

Technical Field

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

[0002] As a drainage treatment performed before the drainage containing organic matter, i.e., organic drainage, is discharged into the environment, biological treatment using microorganisms is generally adopted. In biological treatment, in order to maintain the decomposition activity of organic matter based on microorganisms at a high level, it is necessary to optimize environmental conditions such as water temperature and pH, and add nutrients such as nitrogen, phosphorus, and trace metals. The control of biological treatment also includes determining the amount of nutrients added. Compared with the drainage of public sewers into which domestic drainage flows, the drainage from factories is prone to lack of nutrients. In particular, in the drainage from chemical plants and semiconductor manufacturing plants, the shortage of nutrients required for biological treatment is significant.

[0003] The recommended amount of nutrients added to the raw water as organic wastewater is proportional to the organic matter concentration in the raw water. Assuming that the organic matter concentration in the raw water is represented by biochemical oxygen demand (BOD), the preferred amount of nitrogen (N) and phosphorus (P) added as nutrients in the wastewater treatment based on aerobic microorganisms, i.e., aerobic biological treatment, is, for example, BOD:N:P=100:5:1 on a mass basis. It is difficult to measure the BOD of raw water online or in a short period of time. However, since the determination of the total organic carbon (TOC) concentration in water can be performed online, the correlation between the TOC concentration and BOD in the raw water is obtained in advance, and the TOC concentration of the raw water is monitored by an online TOC concentration meter. On this basis, it is 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 discloses such control of the amount of nitrogen and phosphorus added.

[0004] When wastewater treatment is performed using aerobic microorganisms, fully aerobic conditions are usually established when the dissolved oxygen (DO) concentration in the water in the reaction tank is 3 mg / L or higher. In biological treatment under fully aerobic conditions, the sulfur component in organic wastewater is oxidized into sulfate ions (SO4 2- ). For aerobic biological treatment, biological treatment using anaerobic microorganisms is called anaerobic biological treatment. For example, in anaerobic biological treatment such as methane fermentation, as described in Patent Document 2, it is known that corrosive gases such as hydrogen sulfide are generated.

[0005] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2001-334285 Patent Document 2: Japanese Patent Application Publication No. 2005-81264 Summary of the invention Technical problem to be solved by the invention In the method of controlling the amount of nutrients added based on the TOC concentration measured online, the inside of the piping of the online TOC concentration meter is clogged due to the accumulation of suspended solids (SS), oil, the formation of biofilm, etc., and the measured value becomes unstable, resulting in the inability to stably perform the biological treatment itself. In addition, when aerobic biological treatment is performed under conditions of high BOD volume load, there is also a problem that the treatment becomes unstable.

[0006] An object of the present invention is to provide a wastewater treatment method and a wastewater treatment apparatus capable of stably performing aerobic biological treatment when performing aerobic biological treatment of organic wastewater.

[0007] Technical solutions to solve problems The inventors of the present invention have found that when performing aerobic biological treatment of organic wastewater, the concentration of carbon dioxide generated by the water in the reaction tank is measured, and the amount of nutrients to be added can be determined from the measured carbon dioxide concentration. Since the measurement of carbon dioxide concentration is performed in the gas phase, it is possible to avoid the problems of suspended matter, accumulation of oil, formation of biofilm, etc. in the measurement of TOC concentration. In addition, the inventors of the present invention have found that when biological treatment of organic wastewater containing sulfur compounds is performed under completely aerobic conditions where the dissolved oxygen (DO) concentration in the water in the reaction tank is 3 mg / L or more, if the volumetric load of organic matter in the biological treatment is large, for example, if the BOD volumetric load exceeds 1.5 kg / m 3 / day, hydrogen sulfide, which should be a product of anaerobic treatment, may be produced. Hydrogen sulfide may damage sensors used to measure carbon dioxide concentration. Similarly, if organic wastewater contains nitrogen compounds, ammonia may be produced even in biological treatment under completely aerobic conditions if the BOD volume load is large. Ammonia may have an adverse effect on the wiring inside the sensor, so ammonia is also considered a corrosive gas.

[0008] Therefore, one embodiment of the wastewater treatment method of the present invention is a wastewater treatment method for performing aerobic biological treatment on organic wastewater containing at least one of sulfur compounds and nitrogen compounds in a reaction tank, comprising the following steps: removing corrosive gas from the gas discharged from the water in the self-reaction tank; measuring the carbon dioxide concentration in the gas after the corrosive gas is removed; and controlling the aerobic biological treatment based on the measured carbon dioxide concentration.

[0009] A wastewater treatment device according to one embodiment of the present invention comprises: a reaction tank that performs aerobic biological treatment on organic wastewater containing at least one of sulfur compounds and nitrogen compounds; a removal unit that removes corrosive gas from gas discharged from water in the reaction tank; a measuring unit that measures the concentration of carbon dioxide contained in the gas after the corrosive gas is removed; and a control unit that controls the aerobic biological treatment based on the carbon dioxide concentration measured by the measuring unit.

[0010] As described above, even if the biological treatment of organic wastewater is performed under completely aerobic conditions, if the volume load of organic matter in the biological treatment in the reaction tank is large, corrosive gases such as hydrogen sulfide and ammonia will be generated. In the above-mentioned wastewater treatment method and wastewater treatment device, before measuring the carbon dioxide concentration contained in the gas generated from the reaction tank, the corrosive gas contained in the gas is removed. As a result, it is possible to prevent adverse effects on sensors for measuring carbon dioxide concentration, and it is possible to stably control aerobic biological treatment based on carbon dioxide concentration when performing aerobic biological treatment.

[0011] Effects of the Invention In the wastewater treatment method and wastewater treatment apparatus of the present invention described above, even when the volume load of organic matter in the organic wastewater is large, aerobic biological treatment can be stably performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a figure which shows the wastewater treatment apparatus which concerns on one Embodiment of this invention.

[0013] Figure 2 It is a diagram showing a wastewater treatment device according to another embodiment.

[0014] Figure 3 It is a diagram showing a wastewater treatment device according to still another embodiment. DETAILED DESCRIPTION

[0015] Next, embodiments of the present invention will be described with reference to the drawings.

[0016] The embodiment described below relates to a technique for decomposing and removing organic matter in raw water by biological treatment using aerobic microorganisms, i.e., aerobic biological treatment. In the drainage treatment method based on the present invention, the organic drainage to be the object of decomposition and removal of organic matter is not particularly limited as long as aerobic biological treatment can be applied, and includes drainage from public sewers, drainage discharged from various factories such as food factories, chemical factories, semiconductor manufacturing factories, liquid crystal manufacturing factories, and pulp factories, as well as drainage discharged from business premises in other fields. Compared with drainage in public sewers, in drainage from private factories, the nutrients required to maintain the decomposition activity of microorganisms used in biological treatment are easily insufficient. In particular, in drainage from chemical factories, semiconductor manufacturing factories, and liquid crystal manufacturing factories, the shortage of nutrients is significant. In the drainage treatment method based on the present invention, as aerobic biological treatment, it is preferred to use activated sludge method, membrane separation activated sludge method (MBR), biofilm method based on fluidized bed or fixed bed, or particle method, etc.

[0017] In the wastewater treatment method according to the present invention, aerobic biological treatment is controlled in such a way that aerobic biological treatment is performed under the best possible conditions. In the control of aerobic biological treatment, for example, water temperature, pH, and the amount of air blown into the reaction tank may be controlled, but it is particularly preferred to control the amount of nutrients added to the raw water. In the embodiment described below, as the control of aerobic biological treatment, the amount of nutrients added to the raw water as organic wastewater is controlled, but in the wastewater treatment method according to the present invention, parameters other than the amount of nutrients added may also be controlled.

[0018] In order to optimize the amount of nutrients added to the raw water, in each embodiment, the BOD or TOC concentration of the raw water is not directly measured, but the carbon dioxide concentration in the gas discharged from the water in the reaction tank is measured. Each embodiment is based on aerobic biological treatment. In aerobic biological treatment, a blower for air supply is usually used to supply oxygen-containing gas, such as air, to the reaction tank, and the water in the reaction tank is aerated or aerated. Therefore, it is preferred to measure the flow rate of the gas supplied to the reaction tank or the gas discharged from the reaction tank together with the carbon dioxide concentration. In addition, the amount of nutrients added to the raw water is controlled based on the measured value of the carbon dioxide concentration, or based on the measured value of the carbon dioxide concentration and the flow rate of the gas.

[0019] In the case of controlling based on the measured value of the carbon dioxide concentration and the measured value of the gas flow rate, the organic matter concentration of the raw water can be calculated based on the measured value of the carbon dioxide concentration and the measured value of the flow rate, and the amount of nutrients added to the raw water can be controlled based on the calculated organic matter concentration, or the amount of nutrients added to the raw water can be controlled based on the value calculated 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 can be measured, and the amount of nutrients added to the raw water can be controlled based on the measured value of the carbon dioxide concentration, the measured value of the flow rate, and the measured value of the water quality. As the gas flow rate, the flow rate of air supplied to the reaction tank from the air blower can be measured, or the overall flow rate of the gas discharged from the reaction tank can be measured. In the case of aerobic treatment using a fluidized bed, a screen is arranged in the reaction tank to separate the carrier, and air is also blown into the screen during cleaning. However, at this time, the value obtained by adding the air volume of the blower used for air dispersion and the air volume of the air used for cleaning the screen can be used as the gas flow rate.

[0020] Figure 1 A wastewater treatment device according to one embodiment of the present invention is shown. Figure 1 The wastewater treatment device shown is equipped with a fluidized bed type reaction tank 10, which stores raw water as organic wastewater and performs biological treatment of the raw water under aerobic conditions. The treated water in which organic matter is decomposed and removed by biological treatment is discharged from the reaction tank 10. The reaction tank 10 is filled with a carrier 11, and a diffuser 12 is provided at the bottom of the reaction tank 10 to blow air into the reaction tank 10 for supplying oxygen, that is, for ventilation. An inlet pipe 13 for supplying raw water to the reaction tank 10 is connected to the reaction tank 10. A gas pipe 14 for supplying air to the diffuser 12 is connected to the diffuser 12, and a blower 15 for air supply is provided in the gas pipe 14. As the carrier 11 that can be used here, for example, a plastic carrier, a sponge carrier, a gel carrier, etc. can be cited, but among them, from the viewpoint of cost and durability, a sponge carrier is preferably used. A stirring device for stirring the carrier 11 can also be provided in the reaction tank 10.

[0021] In biological treatment, nutrients are required to maintain the decomposition activity of microorganisms at a high level and to reproduce. If the raw water lacks nutrients, nutrients need to be added to the raw water inside the reaction tank 10 or in the front stage of the reaction tank 10. Nutrients are added to the raw water in the form of a solution, for example. A solution of nutrients is also called a nutrient solution. Figure 1In the drainage treatment device shown, a nutrient storage tank 21 for storing nutrient solution is provided, and the nutrient storage tank 21 is connected to the inlet piping 13 via the nutrient solution piping 22. A pump 23 for feeding the nutrient solution is provided in the nutrient solution piping 22. Therefore, in the drainage treatment device, nutrients can be added to the raw water flowing in the inlet piping 13 and supplied to the reaction tank 10, and by controlling the pump 23, the amount of nutrients added relative to the raw water can be controlled. Nutrients are roughly divided into nutrient salts containing nitrogen and phosphorus and trace elements that are required in less 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. As a nitrogen source, urea and ammonium salts can be used. As a phosphorus source, phosphoric acid and phosphates can be used.

[0022] exist Figure 1 In the wastewater treatment device shown, the amount of nutrients added is controlled based on the carbon dioxide concentration in the gas discharged from the water in the reaction tank 10 by aerobic biological treatment and the flow rate of air supplied to the reaction tank 10 for gas diffusion. Therefore, in the reaction tank 10, a carbon dioxide concentration sensor 31 for measuring the carbon dioxide concentration in the gas discharged from the water in the reaction tank 10 is provided, and in the gas pipe 14 between the blower 15 and the diffuser 12, an air volume meter 32 for measuring the flow rate of air flowing therein is provided. The reaction tank 10 is covered with a cover 16, and the carbon dioxide concentration sensor 31 is provided in the gas phase part in the reaction tank 10, in the pipe connected to the gas phase part, etc. Since it is necessary to avoid condensation of the carbon dioxide concentration sensor 31, when it is provided in the pipe, the pipe can also be kept warm, and a moisture separator and an air dryer are provided at a position directly in front of the carbon dioxide concentration sensor 31.

[0023] When 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 is inserted under the water surface while minimizing the opening of the upper part of the reaction tank 10, and a carbon dioxide concentration sensor 31 is arranged at a position above the water surface in the pipe. 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 absorption method (NDIR) is particularly preferably used. The measurement of carbon dioxide concentration can be performed manually (manual) or online.

[0024] As can be seen from the examples and comparative examples described below, even if the dissolved oxygen (DO) concentration of the water in the reaction tank 10 is set to 3 mg / L or more and the conditions are completely aerobic, if the BOD volume load of the aerobic biological treatment in the reaction tank 10 is large, for example, exceeding 1.5 kg / m 3 / day, hydrogen sulfide derived from sulfur compounds contained in the raw water may also be produced. In addition, ammonia derived from nitrogen compounds may also be produced. Hydrogen sulfide and ammonia are corrosive gases and may corrode the inside of the carbon dioxide concentration sensor 31. If the carbon dioxide concentration sensor 31 is damaged by corrosive gases, it will be difficult to obtain a stable measurement value and it will be difficult to properly control the amount of nutrients added. Therefore, Figure 1 In the wastewater treatment device shown, before the carbon dioxide concentration of the gas discharged from the water in the reaction tank 10 is measured by the carbon dioxide concentration sensor 31, a pretreatment for removing corrosive gas from the gas is performed. As a general method for removing hydrogen sulfide, there are a method of removing it in the form of iron sulfide by contacting it with iron oxide, a method of removing it by absorption by an alkaline agent such as sodium hydroxide, etc. However, in the method using an alkaline agent, carbon dioxide is also absorbed and removed, so the method using iron oxide is preferably used in this embodiment.

[0025] exist Figure 1 In the example shown, the raw water as organic wastewater contains sulfur compounds and may generate hydrogen sulfide. The carbon dioxide concentration sensor 31 is arranged inside the tubular member 51, and a desulfurization filter 52 is provided at one end of the tubular member 51. The gas is made to flow in one direction in the tubular member 51 as shown by the arrow in the figure by a fan, an air pump, etc., which are not shown in the figure, and the gas from which hydrogen sulfide is removed by the desulfurization filter 52 is supplied to the carbon dioxide concentration sensor 31. In the figure, the other end of the tubular member 51 is also located inside the reaction tank 10, but the tubular member 51 can also be provided in a manner that penetrates the cover 16 to discharge the gas measured by the carbon dioxide concentration sensor 31 to the outside of the reaction tank 10. The desulfurization filter 52 is a filter that removes hydrogen sulfide using iron oxide, for example, filled with a filler containing iron oxide. The filler can be, for example, granular or cylindrical with a diameter of 4 to 12 mm, or can be processed into a porous honeycomb. From the perspective of high processing performance, it is preferred to use a honeycomb filler. The space velocity (SV) of the gas in the desulfurization filter 52 is, for example, 10 to 180 h -1 about.

[0026] Next, Figure 1 The control of the amount of nutrients added to the wastewater treatment device shown in the figure is explained. It is recommended that the amount of nutrients (nutrient salts and trace metals) added to the raw water be proportional to the organic matter concentration in the raw water, preferably proportional to the BOD. 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. Figure 1In the wastewater treatment device shown, 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 discharged from the water in the reaction tank 10 by aerobic biological treatment and the flow rate of air supplied to the reaction tank 10 for gas dispersion are measured. Then, the BOD value of the raw water is calculated based on the measured value of the carbon dioxide concentration and the measured value of the air flow rate, and the amount of nutrients added is determined based on the calculated BOD value. To this end, first, the combination of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 and the measured value of the air volume obtained by the air volume meter 32 is used as the input value (Xn), and the BOD concentration of the raw water corresponding to the input value (Xn) is used as the output value (Yn). On the basis of obtaining a certain number of combinations of input values ​​and output values ​​in advance, a model or a relational expression is created. The number of combinations obtained is, for example, tens to hundreds of groups. At this time, instead of using the combination of the carbon dioxide concentration and the air volume as the input value (Xn), the value obtained by multiplying the carbon dioxide concentration and the air volume as the product value can be used as the input value (Xn). In the case of the method based on the multiplication value, if the air volume is constant, only the measured value of the carbon dioxide concentration may be used instead of the multiplication value.

[0027] Once the model is created, the combination of the measured value of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 and the measured value of the air volume obtained by the air volume meter 32 is then input into the model, and as a result, the pump 23 is driven based on the BOD concentration value output from the model to control whether or not nutrients are added to the raw water and the amount of addition. In order to perform such control, the wastewater treatment device includes a control device 40, which holds the created model, applies the carbon dioxide concentration value obtained by the carbon dioxide concentration sensor 31 and the measured value obtained by the air volume meter 32 to the model to calculate the BOD concentration value of the raw water, and controls the start and stop of the pump 23 and the flow rate based on the BOD concentration value. In addition, although the BOD concentration is used in the creation of the model, since it can be considered that the created model itself is a model that directly outputs the amount of nutrients to be added by taking the measured value of the carbon dioxide concentration and the measured value of the air volume as inputs, once the model is created, it is possible to determine the optimal amount of nutrients to be added without explicitly calculating the BOD concentration value based on the measured value of the carbon dioxide concentration and the measured value of the air volume.

[0028] Next, the creation of the model is described. When an input value is input, the model that outputs the BOD concentration of the raw water corresponding to it as an output value can be created using, for example, various regression analyses. In particular, if the model is created by supervised learning using a neural network technique, the accuracy of the control of the amount of nutrient addition is improved. The carbon dioxide concentration obtained by the carbon dioxide concentration sensor 31 sometimes varies according to the structure and size of the reaction tank 10, the size of the gas phase in the reaction tank 10, the type of biological treatment, etc. In addition, the air volume supplied to the reaction tank 10 for gas dispersion also varies according to the structure and size of the reaction tank 10, etc. Therefore, the model can also be set for each reaction tank 10. Furthermore, depending on the type or origin of the raw water, the relationship between the BOD of the raw water and the measured carbon dioxide concentration and air volume may also vary. Therefore, it is also possible to prepare a model for each type and origin of the raw water, and select a model for the control of the amount of nutrient addition from the prepared models according to the type and origin of the raw water.

[0029] exist Figure 1 In the wastewater treatment device shown, the air volume meter 32 is provided in the gas piping 14 to measure the flow rate of the air supplied to the reaction tank 10 through the gas piping 14, that is, the air volume. However, instead of measuring the flow rate of the air supplied to the reaction tank 10, the flow rate of the gas discharged from the reaction tank 10 may be measured. In the case of measuring the flow rate of the gas discharged from the reaction tank 10, when the reaction tank 10 is completely covered by the cover 16, the air volume meter 32 may be provided in the piping connected to the inside of the reaction tank 10 in order 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 the external gas on the measurement result, a cylindrical piping or the like is inserted under the water surface on the basis of minimizing the opening portion of the upper part of the reaction tank 10, and the air volume meter 32 is provided in the piping.

[0030] In order to control the amount of nutrients added to the raw water, it is also considered to use an online TOC concentration meter to measure the organic matter concentration in the raw water online. However, the online TOC concentration meter has a thin pipe to introduce a small amount of sample water into the measuring device, which is prone to clogging and unstable measurement values. In contrast, the carbon dioxide concentration sensor 31 performs measurements without contacting water, so the stability of the measurement value is very high. In addition, the gas flow rate can also be measured stably. Therefore, in Figure 1 In the wastewater treatment apparatus shown, the optimum value of the amount of nutrients to be added to the raw water can be stably obtained without directly measuring the concentration of organic matter in the raw water.

[0031] Figure 2 A wastewater treatment device according to another embodiment of the present invention is shown. Figure 2 The drainage treatment device shown in Figure 1In the wastewater treatment device shown in the figure, a water quality measuring unit 33 is provided to measure the water quality of the water in the reaction tank 10, and the measurement result of the water quality measuring unit 33 is also sent to the wastewater treatment device of the control device 40. The water quality items measured by the water quality measuring unit 33 include at least pH, and in addition to pH, water temperature and the like can also be measured. Figure 2 The model used in the wastewater treatment device shown is a model that uses a combination of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31, the air volume measurement value obtained by the air volume meter 32, and the water quality (particularly pH) measurement value measured by the water quality measurement unit 33 as an input (Xn), and uses the BOD concentration of raw water corresponding to the input value (Xn) as an output value (Yn), and is a model created in the same manner as the above-mentioned model. The control device 40 applies the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31, the air volume measurement value obtained by the air volume meter 32, and the water quality (particularly pH) measurement value 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.

[0032] As we all know, in water, CO2 and HCO3 of inorganic carbonic acid - 、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 discharged from the water in the reaction tank 10 may also change depending on the pH. Figure 2 In the wastewater treatment device shown, since the amount of nutrients added is controlled by also considering the pH of the water in the reaction tank 10, the amount of nutrients added can be optimized regardless of the pH of the raw water. In addition, the solubility of carbon dioxide in water depends on the water temperature, but if the solubility of carbon dioxide changes, the concentration of carbon dioxide in the gas discharged from the water in the reaction tank 10 also changes. Therefore, when there is a change in water temperature in the reaction tank 10, the water quality measuring 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.

[0033] In wastewater treatment, a plurality of reaction tanks for biological treatment are sometimes connected in series, and treated water discharged from a preceding reaction tank is introduced into a subsequent reaction tank. By performing biological treatment in each reaction tank, treated water with a high degree of organic matter removal is obtained. Figure 3 is with Figure 1 and Figure 2The device shown is a wastewater treatment device that similarly performs wastewater treatment based on aerobic biological treatment, and represents a wastewater treatment device in which a plurality of reaction tanks 10 are arranged in series, i.e., in multiple stages. In the case where the reaction tanks 10 are arranged in multiple stages of two or more, in the reaction tank 10 of the front stage, the carbon dioxide concentration in the gas discharged from the reaction tank is measured, and the air volume of the air supplied to the reaction tank is measured, and the BOD concentration value of the raw water is calculated based on the carbon dioxide concentration and the air volume. Based on the BOD concentration value, the amount of nutrients added to the raw water supplied to the reaction tank can be controlled. In this case, the pH of the water in the reaction tank 10 of the front 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. Therefore, in Figure 3 In the wastewater treatment device shown in the figure, the carbon dioxide concentration sensor 31, the air volume meter 32 and the water quality measuring unit 33 are only provided in the first stage reaction tank 10, and the 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. Figure 1 The device shown is also provided inside a tubular member 51 having a desulfurization filter 52 at one end. The control device 40 calculates the BOD concentration value of the raw water based on the measured values ​​of the carbon dioxide concentration sensor 31, the air volume meter 32 and the water quality measuring unit 33, and controls the pump 23 for feeding the nutrient solution based on the BOD concentration value.

[0034] When the reaction tanks 10 are arranged in series in two or more stages, most of the organic matter is decomposed and removed in the reaction tank 10 of the first stage, so the organic matter that needs to be removed in the reaction tanks 10 of the second and subsequent stages becomes less. In addition, the microorganisms that have propagated in the reaction tank 10 of the first stage die and disintegrate, and nutrients are dissolved again. For these reasons, even if nutrients are not added to the water supplied to the reaction tanks 10 of the second and subsequent stages, and even if the biological treatment in the reaction tanks 10 of the second and subsequent stages is not specially controlled, biological treatment can be performed in the reaction tanks 10 of the second and subsequent stages, and the overall treatment performance of the wastewater treatment device can be maintained. Therefore, it is not necessary to measure the carbon dioxide concentration, air volume, and pH for the reaction tanks of the second and subsequent stages.

[0035] Example Next, the present invention will be described in further detail by way of Examples, Comparative Examples and Reference Examples.

[0036] [Example 1, Reference Example 1, and Comparative Examples 1 and 2] First, the common experimental conditions in Example 1, Reference Example 1, and Comparative Examples 1 and 2 are described. Figure 1The device shown in the figure is similarly a reaction tank for aerobic biological treatment, constituting a wastewater treatment device. The upper part of the reaction tank is covered with a lid. A sponge carrier made of hydrophobic polyurethane is filled in the reaction tank at a filling rate of 20% by bulk volume. As organic wastewater, wastewater containing isopropyl alcohol is prepared. The BOD concentration of the wastewater is 180 to 330 mg / L, the nitrogen (N) concentration is 10 to 26 mg / L, the phosphorus (P) concentration is less than 0.5 mg / L, and the sulfate ion (SO4 2- ) concentration is 60 to 360 mg / L. Such wastewater is supplied to a reaction tank, where it is aerated and nutrients are added to perform aerobic biological treatment of the wastewater. Phosphoric acid and trace metals are used as nutrients. At this time, the water temperature is about 30°C, the pH of the water in the reaction tank is 6.5 to 7.0, and the dissolved oxygen concentration is 3 mg / L or more, satisfying the completely aerobic conditions.

[0037] In order to measure the carbon dioxide concentration of the gas discharged from the water in the reaction tank, a pipe connected to the gas phase of the reaction tank is set, and the gas is extracted from the pipe by an air pump, and the carbon dioxide concentration of the extracted gas is continuously measured by a carbon dioxide concentration sensor. The carbon dioxide concentration sensor is a sensor of the non-dispersive infrared absorption method (NDIR). The carbon dioxide concentration sensor installed in the reaction tank is called a control sensor. In Example 1, the gas extracted from the pipe is passed in an upward flow into a column filled with a honeycomb filler coated with iron oxide on the surface, and the carbon dioxide concentration of the gas is measured by a control sensor. The column is equivalent to a desulfurization filter. On the other hand, in Comparative Examples 1, 2 and Reference Example 1, a desulfurization filter is not set, and the carbon dioxide concentration of the gas extracted from the pipe is directly measured by a control sensor.

[0038] (Example 1) The BOD volume load of the aerobic biological treatment in the reaction tank was set to 4 kg / m 3 / day, the wastewater treatment device is continuously operated, and after pretreatment using a desulfurization filter, the carbon dioxide concentration is continuously measured using a control sensor. At a time point of about 3 months from the start of operation, the gas generated by the water in the reaction tank is sampled, and the carbon dioxide concentration in the gas is measured using a measuring device different from the control sensor, and compared with the measured value of the control sensor at this time. The carbon dioxide concentration measured here is called the standard gas concentration. As a result, the measured value of the control sensor represents a value of 107% of the standard gas concentration. Considering that the standard gas concentration corresponds to the actual value of the carbon dioxide concentration at this time, in Example 1, the measurement error in the control sensor is within the allowable range.

[0039] (Comparative Example 1) The same experiment was conducted as in Example 1 at a BOD volume load of 4 kg / m 3 The wastewater treatment device was operated continuously under the condition of 100 ppm / day, and the carbon dioxide concentration was continuously measured. As a result, at a time point of about 3 months from the start of operation, a sensor error occurred in the control sensor, and it became impossible to measure the carbon dioxide concentration. In addition, at this time, the hydrogen sulfide concentration of the gas generated from the reaction tank was measured and the result was 0.7 ppm or more.

[0040] (Comparative Example 2) The BOD volume load is set to 3 kg / m 3 / day, except for this, the wastewater treatment device was continuously operated and the carbon dioxide concentration was continuously measured in the same manner as in Comparative Example 1. As a result, at a time point of about 3 months from the start of operation, the carbon dioxide concentration measured by the control sensor was about 140% of the standard gas concentration, which was a state with a large measurement error. In addition, at this time, hydrogen sulfide was detected in the gas generated from the reaction tank.

[0041] (Reference Example 1) The BOD volume load is set to 1.5 kg / m 3 / day, except for this, the wastewater treatment device was continuously operated and the carbon dioxide concentration was continuously measured in the same manner as in Comparative Example 1. As a result, at a time point of about 3 months from the start of operation, the carbon dioxide concentration measured by the control sensor was about 105% of the standard gas concentration, and the measurement error in the control sensor was within the allowable range.

[0042] As can be seen from Reference Example 1 and Comparative Examples 1 and 2, even if the dissolved oxygen concentration of the water in the reaction tank is set to 3 mg / L or more as a completely aerobic condition, when the BOD load capacity exceeds 1.5 kg / m 3 / day, hydrogen sulfide, which should be produced only under anaerobic conditions, will also be produced from the reaction tank. It can also be seen that the carbon dioxide concentration sensor is adversely affected by the hydrogen sulfide. Furthermore, in the case of continuous operation and continuous measurement for about 3 months, the carbon dioxide concentration sensor becomes unable to measure, or shows a large measurement error. In contrast, in Example 1, in which the carbon dioxide concentration is measured after the desulfurization filter is used to remove the hydrogen sulfide even under the condition of hydrogen sulfide generation, the measured value of the carbon dioxide concentration is stable even in the case of long-term continuous operation and continuous measurement. Therefore, it can be seen that by setting a desulfurization filter, the control of adding nutrients based on the carbon dioxide concentration can be optimized for a long time.

[0043] [Reference Examples 2 to 7] The control of aerobic biological treatment by using at least carbon dioxide concentration was studied. First, the common experimental conditions of Reference Examples 2 to 7 are described. Figure 2 The primary reaction tank shown in the figure performs biological treatment based on aerobic treatment of raw water as organic wastewater. Aerobic microorganisms are supported on a sponge carrier containing a hydrophobic polyurethane resin, and such a sponge carrier is filled in the reaction tank at a bulk volume of 20% relative to the volume of the reaction tank. The retention time in the reaction tank is set to 18 hours. As raw water, wastewater containing isopropyl alcohol is used. The BOD concentration in the raw water is about 900 mg / L (set as the reference concentration), the nitrogen (N) concentration in the raw water is less than 2 mg / L, and the phosphorus (P) concentration is less than 0.1 mg. The BOD volume load during biological treatment is about 1 kg / m 3 / day, the water temperature is about 20°C, the dissolved oxygen concentration (DO) of the water in the reaction tank is 2 mg / L or more, and the pH of the water in the reaction tank is 6.0 to 7.5. To diffuse air, air is supplied to the reaction tank at a flow rate of 3 to 5 L / min.

[0044] Nutrients (nitrogen (N) and phosphorus (P)) are added to the raw water in such a way that the BOD:N:P ratio becomes 100:5:1, and the concentration of carbon dioxide discharged from the water in the reaction tank and the pH of the water in the reaction tank are monitored. This monitoring is repeated while intentionally changing the BOD concentration in the raw water from 100% of the reference concentration to 30% and 60%. The fact that the BOD concentration of the raw water can be calculated with high accuracy is equivalent to the high accuracy of the nutrient addition control.

[0045] (Reference Example 2) As a method for calculating the BOD concentration of raw water from the carbon dioxide concentration, the determination coefficient R was calculated by univariate regression analysis for the carbon dioxide concentration and each BOD concentration. 2 , the result is 0.39.

[0046] (Reference Example 3) As a method for calculating the BOD concentration of raw water from the carbon dioxide concentration and the air volume, the determination coefficient R is calculated by multivariate regression analysis for the carbon dioxide concentration, the air volume, and each BOD concentration. 2 , the result is 0.82.

[0047] (Reference Example 4) As a method for calculating the BOD concentration of raw water from the carbon dioxide concentration and the air volume, the product of the measured value of the carbon dioxide concentration and the measured value of the air volume is obtained, and the determination coefficient R is calculated by univariate regression analysis for the product value and each BOD concentration. 2 , the result is 0.83.

[0048] (Reference Example 5) As a method for calculating the BOD concentration of raw water from the carbon dioxide concentration and pH, the determination coefficient R was calculated by multivariate regression analysis for the carbon dioxide concentration, pH, and each BOD concentration. 2 , the result is 0.40.

[0049] (Reference Example 6) As a method for calculating the BOD concentration of raw water from the carbon dioxide concentration, air volume, and pH, the determination coefficient R is calculated by multivariate regression analysis for the carbon dioxide concentration, air volume, pH, and each BOD concentration. 2 , the result is 0.89.

[0050] (Reference Example 7) As a method for calculating the BOD concentration of raw water from the carbon dioxide concentration, air volume and pH, the product of the measured value of the carbon dioxide concentration and the measured value of the air volume is obtained, and the determination coefficient R is calculated by multivariate regression analysis for the product value, pH and each BOD concentration. 2 , the result is 0.96.

[0051] Description of Reference Numerals 10: Reaction tank 11: Carrier 12: Air dispersion device 13: Inlet piping 14: Gas piping 15: Blower 16: Cover 21: Nutrient storage tank 22: Nutrient solution piping 23: Pump 31: Carbon dioxide concentration sensor 32: Air flow meter 33: Water Quality Measurement Department 40: Control device 51: Tubular components 52: Desulfurization filter.

Claims

1. A method for treating drainage, characterized in that: The wastewater treatment method is a wastewater treatment method for performing aerobic biological treatment on organic wastewater containing at least one of sulfur compounds and nitrogen compounds in a reaction tank, and the wastewater treatment method comprises the following steps: removing the corrosive gas from the gas discharged from the water in the reaction tank; measuring the concentration of carbon dioxide in the gas after removing the corrosive gas; as well as The aerobic biological treatment is controlled based on the measured carbon dioxide concentration.

2. The wastewater treatment method according to claim 1, wherein: The BOD treatment load in the reaction tank during the aerobic biological treatment is greater than 1.5 kg / m 3 / sky.

3. The wastewater treatment method according to claim 1 or 2, wherein: The aerobic biological treatment is controlled by controlling the amount of nutrients added relative to the organic drainage.

4. The wastewater treatment method according to claim 1 or 2, wherein: A fluidized bed is formed in the reaction tank to perform the aerobic biological treatment.

5. The wastewater treatment method according to claim 1 or 2, wherein: When a plurality of the reaction tanks are arranged in series, the removal of the corrosive gas and the measurement of the carbon dioxide concentration are performed in the first-stage reaction tank, and the aerobic biological treatment in the first-stage reaction tank is controlled based on the measured carbon dioxide concentration.

6. A drainage treatment device, comprising: A reaction tank for performing aerobic biological treatment on organic wastewater containing at least one of a sulfur compound and a nitrogen compound; a removal unit that removes corrosive gas from gas discharged from water in the reaction tank; a measuring unit for measuring the concentration of carbon dioxide contained in the gas after the corrosive gas is removed; as well as A control unit controls the aerobic biological treatment based on the carbon dioxide concentration measured by the measuring unit.

7. The drainage treatment device according to claim 6, wherein: The BOD treatment load in the reaction tank exceeds 1.5 kg / m 3 The aerobic biological treatment is carried out under the conditions of 1:1 / day.

8. The wastewater treatment device according to claim 6 or 7, wherein: The wastewater treatment device further includes an adding unit for adding nutrients to the organic wastewater. The control unit controls an addition amount of the nutrient substance added by the adding unit based on the carbon dioxide hydrogen concentration.

9. The wastewater treatment device according to claim 6 or 7, wherein: The reaction tank is a fluidized bed type reaction tank.

10. The wastewater treatment device according to claim 6 or 7, wherein: The plurality of reaction tanks are arranged in series, The removal unit and the measurement unit are provided for the front-stage reaction tank. The control unit controls the aerobic biological treatment in the front-stage reaction tank.

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