Wastewater treatment method, and wastewater treatment device

Abstract

To enable stable performance of an aerobic biological treatment by determining the optimum amount of a nutrient to be added to organic wastewater, i.e., raw water, for example, upon carrying out an aerobic biological treatment of organic wastewater.SOLUTION: The wastewater treatment device comprises a reaction tank 10 for carrying out an aerobic biological treatment of organic wastewater at least including one of a sulfur compound and a nitrogen compound, a desulfurization filter 52 that removes corrosive gas such as hydrogen sulfide from gas released from water present in the reaction tank, a carbon dioxide concentration censor 31 that measures the concentration of carbon dioxide contained in the gas removed of the corrosive gas, and a controller 40 that controls the aerobic biological treatment according to the carbon dioxide concentration having been measured.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Biological treatment using microorganisms is commonly used as a wastewater treatment method before releasing organic wastewater, or organic wastewater, into the environment. In biological treatment, it is necessary to optimize environmental conditions such as water temperature and pH, as well as to add nutrients such as nitrogen, phosphorus, and trace metals, in order to maintain high activity of microbial decomposition of organic matter. Controlling biological treatment also includes determining the amount of nutrients to be added. Compared to wastewater from public sewers into which domestic wastewater flows, wastewater from factories tends to be deficient in nutrients. In particular, wastewater from chemical plants and semiconductor manufacturing plants shows a significant deficiency in nutrients necessary 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 biological treatment, are, on a mass basis, for example, BOD:N:P = 100:5:1. Although it is difficult to measure the BOD of raw water online or in a short time, 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, converted to a BOD value, and the amount of nitrogen and phosphorus added is controlled based on the obtained BOD value (for example, Patent Document 1).

[0004] When treating wastewater with aerobic microorganisms, conditions are generally considered fully aerobic 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, sulfur components in organic wastewater are converted into sulfate ions (SO4).2- It is oxidized to ). Biological treatment that uses anaerobic microorganisms is called anaerobic biological treatment, as opposed to aerobic biological treatment. In anaerobic biological treatment such as methane fermentation, it is known that corrosive gases such as hydrogen sulfide are generated, as described in Patent Document 2. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-334285 [Patent Document 2] Japanese Patent Publication No. 2005-81264 [Overview of the project] [Problems that the invention aims to solve]

[0006] In methods that control the amount of nutrients added based on TOC concentration measured online, a problem arises: clogging can occur inside the piping of the online TOC concentration meter due to the accumulation of suspended solids (SS) and oils, and the formation of biofilms, leading to unstable measurements and, consequently, making it impossible to perform the biological treatment stably. Similarly, when performing aerobic biological treatment under conditions of high BOD volumetric loading, the treatment may become unstable.

[0007] The object of the present invention is to provide a wastewater treatment method and a wastewater treatment apparatus that can stably perform aerobic biological treatment when treating organic wastewater with aerobic biological agents. [Means for solving the problem]

[0008] The inventors have discovered that when performing aerobic biological treatment of organic wastewater, the concentration of carbon dioxide generated from the water in the reaction vessel can be 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, problems such as the accumulation of suspended solids and oils and the formation of biofilms, which occur in TOC concentration measurement, can be avoided. Furthermore, the inventors have found that when performing biological treatment of organic wastewater containing sulfur compounds under completely aerobic conditions where the dissolved oxygen (DO) concentration in the water in the reaction vessel is 3 mg / L or higher, if the volumetric load of organic matter in the biological treatment is large, for example, it can be expressed as a BOD volumetric load of 1.5 kg / m³. 3 We found that when the BOD volume load exceeds a certain limit, hydrogen sulfide, which should be a by-product of anaerobic treatment, can be generated. Hydrogen sulfide can damage sensors used to measure carbon dioxide concentration. Similarly, if organic wastewater contains nitrogen compounds, ammonia and other substances may be generated even under fully aerobic biological treatment conditions if the BOD volume load is high. Ammonia is also considered a corrosive gas because it can adversely affect the wiring inside sensors.

[0009] Accordingly, the wastewater treatment method of the present invention is a wastewater treatment method in which aerobic biological treatment is performed on organic wastewater containing at least one of a sulfur compound and a nitrogen compound in a reaction tank, characterized in that corrosive gases are removed from the gas released from the water in the reaction tank, the carbon dioxide concentration in the gas after the corrosive gases have been removed is measured, and the aerobic biological treatment is controlled based on the measured carbon dioxide concentration.

[0010] The wastewater treatment apparatus of the present invention comprises a reaction tank that performs aerobic biological treatment on organic wastewater containing at least one of a sulfur compound and a nitrogen compound; a removal means for removing corrosive gases from the gas released from the water in the reaction tank; a measuring means for measuring the carbon dioxide concentration contained in the gas after the corrosive gases have been removed; and a control means for controlling the aerobic biological treatment based on the carbon dioxide concentration measured by the measuring means.

[0011] As described above, even when biological treatment of organic wastewater is carried out under fully aerobic conditions, if the volumetric 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 present invention, before measuring the carbon dioxide concentration contained in the gas generated from the reaction tank, the corrosive gas contained in the gas is removed. Thereby, it is possible to prevent adverse effects on sensors for measuring the carbon dioxide concentration, and it becomes possible to stably control the aerobic biological treatment based on the carbon dioxide concentration when performing the aerobic biological treatment.

Advantages of the Invention

[0012] According to the present invention, it becomes possible to stably perform aerobic biological treatment even when the volumetric load of organic matter in organic wastewater is large.

Brief Description of the Drawings

[0013] [Figure 1] It is a diagram showing a wastewater treatment apparatus according to an embodiment of the present invention. [Figure 2] It is a diagram showing a wastewater treatment apparatus according to another embodiment. [Figure 3] It is a diagram showing a wastewater treatment apparatus according to yet another embodiment.

Modes for Carrying Out the Invention

[0014] Next, embodiments of the present invention will be described with reference to the drawings.

[0015] The present invention relates to a technology for performing biological treatment (i.e., aerobic biological treatment) using aerobic microorganisms on raw water that 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 aerobic biological treatment is applicable. For example, it includes wastewater discharged from public sewers, wastewater discharged from various factories such as food factories, chemical factories, semiconductor manufacturing factories, liquid crystal manufacturing factories, and paper pulp factories, and further includes wastewater discharged from business establishments in other fields. Compared with wastewater from public sewers, in wastewater from private factories, nutrients necessary to maintain a high decomposition activity of the microorganisms used in biological treatment are likely to be insufficient. In particular, in wastewater from chemical factories, semiconductor manufacturing factories, and liquid crystal manufacturing factories, the shortage of nutrients is significant. In the present invention, aerobic biological treatment is carried out by methods such as the activated sludge method, the membrane separation activated sludge method (MBR), the biological membrane method using a fluidized bed or a fixed bed, or the granule method.

[0016] The wastewater treatment method according to the present invention controls the aerobic biological treatment so that the aerobic biological treatment is carried out under the most optimal conditions as much as possible. In the control of aerobic biological treatment, for example, it is possible to control the water temperature, pH, and the amount of air blown into the reaction tank. In particular, it is preferable to control the amount of nutrients added to the raw water. In the embodiments described below, as the control of aerobic biological treatment, the amount of nutrients added to the raw water, which is organic wastewater, is controlled. However, in the present invention, parameters other than the amount of nutrients added may also be controlled.

[0017] In order to optimize the amount of nutrients added to the raw water, this embodiment measures the carbon dioxide concentration in the gas released from the water in the reaction vessel, rather than directly measuring the BOD or TOC concentration of the raw water. This embodiment assumes aerobic biological treatment, in which oxygen-containing gas, such as air, is usually supplied to the reaction vessel using a blower or the like to perform aeration or diffusion treatment on the water in the reaction vessel. Therefore, it is preferable to measure the flow rate of the gas supplied to the reaction vessel or the gas released from the reaction vessel, along with the carbon dioxide concentration. Then, the amount of nutrients added to the raw water is controlled based on the measured carbon dioxide concentration, or based on the measured carbon dioxide concentration and gas flow rate.

[0018] When controlling the reaction based on measured carbon dioxide concentration and gas flow rate, the organic matter concentration of the raw water may be calculated from the measured carbon dioxide concentration and flow rate, and the amount of nutrients added to the raw water may be controlled based on the calculated organic matter concentration, or the amount of nutrients added to the raw water may be controlled based on the product of the measured concentration and the measured flow rate. Furthermore, the water quality (e.g., pH) of the water in the reaction vessel may be measured, and the amount of nutrients added to the raw water may be controlled based on the measured carbon dioxide concentration, flow rate, and water quality. As the gas flow rate, the flow rate of air supplied to the reaction vessel from a blower for ventilation may be measured, or the total flow rate of gas released from the reaction vessel may be measured. When performing aerobic treatment using a fluidized bed, a screen is placed in the reaction vessel to separate the carrier, and air is also blown in to wash the screen. In this case, the sum of the airflow rate from the blower for diffusion and the airflow rate for screen washing may be used as the gas flow rate.

[0019] Figure 1 shows a wastewater treatment apparatus according to one embodiment of the present invention. The wastewater treatment apparatus shown in Figure 1 includes a fluidized bed type reaction tank 10 that stores raw water, which is organic wastewater, and performs biological treatment of the raw water under aerobic conditions. 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 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 in order to supply oxygen, i.e., for aeration. 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 supplying air is provided in the gas pipe 14. Examples of carriers 11 that can be used here include plastic carriers, sponge-like carriers, and gel-like carriers, but among these, a sponge-like carrier is preferred from the viewpoint of cost and durability. The reaction tank 10 may also be provided with a stirring device for stirring the carrier 11.

[0020] In biological treatment, nutrients are necessary for microorganisms to maintain high decomposition activity and proliferate. If the raw water is deficient in nutrients, it is necessary to add nutrients to the raw water in or before the reaction tank 10. In the wastewater treatment device shown in Figure 1, a nutrient storage tank 21 is provided to store a nutrient solution (i.e., nutrient solution), and the nutrient storage tank 21 and the inlet pipe 13 are connected via a nutrient solution pipe 22. A pump 23 for supplying the nutrient solution is provided in the nutrient solution pipe 22. 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 broadly divided into nutrient salts containing nitrogen and phosphorus, and trace elements which 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 nitrogen sources. Phosphate or phosphate can be used as a phosphorus source.

[0021] In the wastewater treatment system shown in Figure 1, 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 aerobic biological treatment and the flow rate of air supplied to the reaction tank 10 for aeration. For this reason, the reaction tank 10 is equipped with a carbon dioxide concentration sensor 31 to measure the carbon dioxide concentration in the gas released from the water in the reaction tank 10, and an air flow meter 32 is provided in the gas piping 14 between the blower 15 and the aeration device 12 to measure the flow rate of air flowing through it. Assuming that the reaction tank 10 is covered by a lid 16, the carbon dioxide concentration sensor 31 is installed in the gas phase section of the reaction tank 10 or in the piping connected to this gas phase section. To avoid condensation on the carbon dioxide concentration sensor 31, if it is installed in the piping, measures such as heat insulation of the piping should be taken, and a mist separator or air dryer may be installed directly in front of the carbon dioxide concentration sensor 31.

[0022] If the reaction vessel 10 is an open system, in order to reduce the influence of outside air on the measurement results, the open portion at the top of the reaction vessel 10 can be made as small as possible, and a cylindrical pipe or the like can be inserted below the water surface, with the carbon dioxide concentration sensor 31 placed in the pipe at a position above the water surface. 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 non-dispersive infrared absorption (NDIR). The measurement of carbon dioxide concentration may be performed manually or online.

[0023] As will become clear from the examples and comparative examples described later, even when the dissolved oxygen (DO) concentration of water in the reaction vessel 10 is 3 mg / L or higher and the conditions are completely aerobic, the BOD volume load of the aerobic biological treatment in the reaction vessel 10 is large, for example, 1.5 kg / m³. 3When the amount exceeds 1 / day, hydrogen sulfide may be generated from sulfur compounds in the raw water. Ammonia and other gases may also be generated from nitrogen compounds. 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 becomes difficult to obtain stable measurement values ​​and to properly control the amount of nutrients added. Therefore, in the wastewater treatment device shown in Figure 1, before measuring the carbon dioxide concentration of the gas released from the water in the reaction tank 10 with the carbon dioxide concentration sensor 31, a pretreatment is performed to remove corrosive gases from the gas. Common methods for removing hydrogen sulfide include contacting it with iron oxide to remove it as iron sulfide, and absorbing it with an alkaline agent such as sodium hydroxide. However, the alkaline agent method also absorbs and removes carbon dioxide, so in this embodiment, the method using iron oxide is preferred.

[0024] In the example shown in Figure 1, assuming that the raw water, which is organic wastewater, contains sulfur compounds and may generate hydrogen sulfide, the carbon dioxide concentration sensor 31 is placed inside the tubular member 51, and a desulfurization filter 52 is provided at one end of the tubular member 51. Gas flows in one direction inside the tubular member 51 as shown by the arrows in the figure, by means of a fan or air pump (not shown), and the gas, from which hydrogen sulfide has been removed after passing through 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 inside the reaction vessel 10, but the tubular member 51 may be provided so as to penetrate the lid 16, and the gas measured by the carbon dioxide concentration sensor 31 may be discharged to the outside of the reaction vessel 10. The desulfurization filter 52 is a filter that removes hydrogen sulfide using iron oxide, and is filled with, for example, a packing material containing iron oxide. The packing material may be, for example, granular or cylindrical with a diameter of 4 to 12 mm, or processed into a porous honeycomb shape. Due to its high processing performance, it is preferable to use a honeycomb-shaped packing material. The space velocity (SV) of the gas in the desulfurization filter 52 is, for example, 10 to 180 h. -1 It is considered to be of a certain degree.

[0025] Next, the control of the amount of nutrients added in the wastewater treatment system shown in Figure 1 will be explained. When adding nutrients (nutrients and trace metals) to raw water, it is recommended that the amount added be proportional to the organic matter concentration in the raw water, preferably BOD. For example, it is recommended that the amounts of nitrogen (N) and phosphorus (P) added in aerobic treatment be BOD:N:P = 100:5:1 on a mass basis. In the wastewater treatment system shown in Figure 1, the BOD of the raw water is not measured by an online TOC concentration meter or the like. Instead, the carbon dioxide concentration in the gas released from the water in the reaction tank 10 by aerobic biological treatment and the flow rate (i.e., airflow rate) of the air supplied to the reaction tank 10 for aeration are measured. The BOD value of the raw water is then calculated from the measured carbon dioxide concentration and the measured air flow rate, and the amount of nutrients to be added is determined based on the calculated BOD value. To achieve this, first, the combination of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 and the measured airflow rate obtained by the airflow 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). A certain number of combinations of input and output values ​​(for example, several dozen to one hundred sets) are acquired in advance, and then a model (or relational equation) is created. At this time, instead of using the combination of the measured carbon dioxide concentration and airflow rate as the input value (Xn), the value obtained by multiplying the measured carbon dioxide concentration and the measured airflow rate (i.e., the multiplied value) may be used as the input value (Xn). In the case of the multiplied value method, if the airflow rate is constant, only the measured carbon dioxide concentration can be used instead of the multiplied value.

[0026] Once the model is created, the combination of carbon dioxide concentration measurements from the carbon dioxide concentration sensor 31 and airflow measurements from the airflow meter 32 is input to the model. Based on the resulting BOD concentration value output from the model, the pump 23 is driven to control whether or not nutrients are added to the raw water and the amount added. To perform this control, the wastewater treatment device has a control device 40 that holds the created model, applies the carbon dioxide concentration value obtained from the carbon dioxide concentration sensor 31 and the measurement value obtained from the airflow meter 32 to the model to calculate the BOD concentration value of the raw water, and controls the start / stop and flow rate of the pump 23 based on the BOD concentration value. Although 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, taking the carbon dioxide concentration measurement and the airflow measurement as input. 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 carbon dioxide concentration measurement and the airflow measurement.

[0027] Next, we will explain how to create a model. A model that outputs the corresponding BOD concentration of raw water as an output value when an input value is received can be created, for example, using various regression analyses. In particular, creating a model using supervised learning with neural network technology improves the accuracy of controlling the amount of nutrients added. The carbon dioxide concentration obtained by the carbon dioxide concentration sensor 31 may vary depending on the configuration and size of the reaction vessel 10, the size of the gas phase in the reaction vessel 10, the type of biological treatment, etc. Also, the airflow rate supplied to the reaction vessel 10 for aeration also changes depending on the configuration and size of the reaction vessel 10, so a model may be set up for each reaction vessel 10. Furthermore, the relationship between the BOD of raw water and the measured carbon dioxide concentration and airflow rate may also vary depending on the type or source of raw water, so a model can be prepared for each type or source of raw water, and a model can be selected from the prepared models according to the type or source of raw water to be used for controlling the amount of nutrients added.

[0028] In the wastewater treatment apparatus shown in Figure 1, an airflow meter 32 is installed in the gas piping 14 to measure the flow rate of air supplied to the reaction vessel 10 via the gas piping 14, i.e., the airflow rate. However, instead of measuring the flow rate of air supplied to the reaction vessel 10, the flow rate of gas released from the reaction vessel 10 may be measured. When measuring the flow rate of gas released from the reaction vessel 10, if the reaction vessel 10 is completely covered by the lid 16, the airflow meter 32 can be installed in a pipe that communicates with the inside of the reaction vessel 10 for the purpose of discharging gas to the outside. If 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 can be made as small as possible, and a cylindrical pipe or the like can be inserted below the water surface, and the airflow meter 32 can be installed in that pipe.

[0029] To control the amount of nutrients added to the raw water, it is conceivable to measure the organic matter concentration in the raw water online using an online TOC concentration meter. However, online TOC concentration meters have narrow piping to draw in a small amount of sample water into the measuring device, making them prone to clogging and resulting in unstable measurements. In contrast, the carbon dioxide concentration sensor 31 performs measurements without contact with water, resulting in very stable measurements. It can also reliably measure gas flow rates. Therefore, in the wastewater treatment device shown in Figure 1, it becomes possible to reliably determine the optimal amount of nutrients to add to the raw water without directly measuring the organic matter concentration in the raw water.

[0030] Figure 2 shows a wastewater treatment apparatus of another embodiment of the present invention. The wastewater treatment apparatus shown in Figure 2 is the same as the wastewater treatment apparatus shown in Figure 1, but is equipped with a water quality measuring unit 33 for measuring the water quality of the water in the reaction tank 10, and the measurement results from the water quality measuring unit 33 are also sent to the control device 40. The water quality parameters measured by the water quality measuring unit 33 include at least pH, and other parameters such as water temperature may also be measured. The model used in the wastewater treatment apparatus shown in Figure 2 takes a combination of carbon dioxide concentration measured by a carbon dioxide concentration sensor 31, airflow measurement values ​​obtained by an anemometer 32, and water quality (especially pH) measurement values ​​measured by the water quality measuring unit 33 as input (Xn), and the BOD concentration of the raw water corresponding to the input value (Xn) as the 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, airflow measurement values ​​obtained by an anemometer 32, and water quality (especially pH) measurement values ​​measured by the water quality measuring unit 33 to the model to calculate the BOD concentration value of the raw water, and controls the pump 23 based on the BOD concentration value.

[0031] As is well known, in water, inorganic carbon dioxide is CO2 and HCO3 depending on the pH. - CO3 2- And its form changes. 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 Figure 2, the amount of nutrients added is controlled by also considering the pH of the water in the reaction tank 10, so the amount of nutrients added can be optimized regardless of the pH of the raw water. Also, 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 will also change. Therefore, if there are fluctuations in the water temperature in the reaction tank 10, the water quality measurement unit 33 can measure 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, airflow rate and pH.

[0032] In wastewater treatment, multiple reaction tanks that perform biological treatment are connected in series, and treated water discharged from the preceding reaction tank is guided to the next reaction tank and biological treatment is performed in each reaction tank to obtain treated water from which organic matter has been highly removed. Figure 3 shows a wastewater treatment apparatus that performs wastewater treatment by aerobic biological treatment, similar to those shown in Figures 1 and 2, in which multiple reaction tanks 10 are provided in series, i.e., in multiple stages. When the reaction tanks 10 are provided in two or more stages, the carbon dioxide concentration in the gas released from the reaction tank 10 and the airflow rate supplied to the reaction tank are measured, and the BOD concentration value of the raw water is calculated from the carbon dioxide concentration and airflow rate, and the amount of nutrients added to the raw water supplied to the reaction tank can be controlled based on that BOD concentration value. In this case, the pH of the water in the preceding reaction tank 10 is also measured, and the amount of nutrients added to the raw water can be controlled based on the carbon dioxide concentration, airflow rate and pH. Therefore, in the wastewater treatment apparatus shown in Figure 3, the carbon dioxide concentration sensor 31, airflow meter 32, and water quality measuring unit 33 are installed only in the foremost 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 foremost reaction tank 10. The carbon dioxide concentration sensor 31 is installed inside a tubular member 51, which has a desulfurization filter 52 at one end, similar to the one shown in Figure 1. The control device 40 calculates the BOD concentration value of the raw water from the measurements of the carbon dioxide concentration sensor 31, airflow meter 32, and water quality measuring unit 33, and controls the pump 23 that supplies the nutrient solution based on the BOD concentration value.

[0033] When two or more reaction tanks 10 are arranged in series, most of the organic matter is decomposed and removed in the first reaction tank 10, so less organic matter needs to be removed in the second and subsequent reaction tanks 10. In addition, nutrients are re-eluted when the microorganisms that have grown in the first reaction tank 10 die and break down. 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 them again, and without performing any special control over the biological treatment in the second and subsequent reaction tanks 10, thus maintaining the overall treatment performance of the wastewater treatment system. For this reason, it is not necessary to measure carbon dioxide concentration, airflow rate, and pH in the second and subsequent reaction tanks. [Examples]

[0034] Next, the present invention will be described in more detail with reference to examples, comparative examples, and reference examples.

[0035] [Example 1, Reference Example 1, and Comparative Examples 1, 2] First, the test conditions common to Example 1, Reference Example 1, and Comparative Examples 1 and 2 will be described. A wastewater treatment apparatus was constructed using a reaction tank that performs aerobic biological treatment similar to that shown in Figure 1. The top of the reaction tank was covered with a lid. The reaction tank was filled with a hydrophobic polyurethane sponge carrier to a bulk volume of 20%. Isopropyl alcohol-containing wastewater was prepared as organic wastewater. The BOD concentration of the wastewater was 180-330 mg / L, the nitrogen (N) concentration was 10-26 mg / L, the phosphorus (P) concentration was 0.5 mg / L or less, and the sulfate ion (SO4) concentration was 0.5 mg / L or less. 2- The concentration was 60-360 mg / L. This wastewater was supplied to a reaction vessel, where aeration was performed and nutrients were added to carry out aerobic biological treatment of the wastewater. Phosphate and trace metals were used as nutrients. At this time, the water temperature was approximately 30°C, the pH of the water in the reaction vessel was 6.5-7.0, and the dissolved oxygen concentration was 3 mg / L or higher, satisfying the conditions for complete aerobic conditions.

[0036] In order to measure the carbon dioxide concentration of the gas released from the water in the reaction tank, a pipe communicating with the gas phase part of the reaction tank was provided, gas was withdrawn from this pipe by an air pump, and the carbon dioxide concentration of the withdrawn gas was continuously measured by a carbon dioxide concentration sensor. The carbon dioxide concentration sensor is of the non-dispersive infrared absorption method (NDIR). The carbon dioxide concentration sensor attached to this reaction tank will be referred to as the control sensor. In Example 1, the gas withdrawn from the pipe was passed upward through a column filled with a honeycomb-shaped filler coated with iron oxide on the surface, and then the carbon dioxide concentration of the gas was measured with the control sensor. This column corresponds to a desulfurization filter. On the other hand, in Comparative Examples 1, 2 and Reference Example 1, without providing a desulfurization filter, the carbon dioxide concentration of the gas withdrawn from the pipe was directly measured with the control sensor.

[0037] (Example 1) The continuous operation of the wastewater treatment device was carried out with the BOD volumetric loading of aerobic biological treatment in the reaction tank being 4 kg / m 3 / day, and after pretreatment with a desulfurization filter, continuous measurement of the carbon dioxide concentration was carried out with the control sensor. When about 3 months had passed since the start of the operation, the gas generated from the water in the reaction tank was sampled, and the carbon dioxide concentration (referred to as the standard gas concentration) in this gas was measured using a measuring device different from the control sensor, and compared with the measured value of the control sensor at that time. As a result, the measured value by the control sensor showed a value of 107% of the standard gas concentration. The standard gas concentration is considered to correspond to the actual value of the carbon dioxide concentration at that time, and in Example 1, the measurement error in the control sensor was within the allowable range.

[0038] (Comparative Example 1) The BOD volumetric loading was 4 kg / m 3The wastewater treatment system was operated continuously under the condition of 1 / day, and the carbon dioxide concentration was also continuously measured. As a result, approximately 3 months after the start of operation, the control sensor showed a sensor error, making it impossible to measure the carbon dioxide concentration. At the same time, the hydrogen sulfide concentration of the gas generated from the reaction vessel was measured to be 0.7 ppm or higher.

[0039] (Comparative Example 2) BOD volumetric load 3 kg / m 3 The wastewater treatment system was operated continuously, and the carbon dioxide concentration was continuously measured, in the same manner as in Comparative Example 1, except that the setting was / day. As a result, approximately three months after the start of operation, the carbon dioxide concentration measured by the control sensor was approximately 140% of the standard gas concentration, indicating a large measurement error. At this time, hydrogen sulfide was also detected from the gas generated from the reaction vessel.

[0040] (Reference example 1) BOD volumetric load of 1.5 kg / m 3 The wastewater treatment device was operated continuously in the same manner as in Comparative Example 1, except that the setting was / day, and the carbon dioxide concentration was also continuously measured. As a result, approximately three months after the start of operation, the carbon dioxide concentration measured by the control sensor was approximately 105% of the standard gas concentration, and the measurement error in the control sensor was within the acceptable range.

[0041] From Reference Example 1 and Comparative Examples 1 and 2, even under fully aerobic conditions with a dissolved oxygen concentration of 3 mg / L or higher in the water in the reaction vessel, the BOD load capacity is 1.5 kg / m³. 3It was found that when the carbon dioxide concentration exceeds 1 / day, hydrogen sulfide, which should only be generated under anaerobic conditions, is produced from the reaction vessel, and that this hydrogen sulfide adversely affects the carbon dioxide concentration sensor. After approximately 3 months of continuous operation and measurement, the carbon dioxide concentration sensor became unable to measure or began to show large measurement errors. In contrast, in Example 1, where hydrogen sulfide was removed by a desulfurization filter before measuring the carbon dioxide concentration, even under similar conditions where hydrogen sulfide was generated, the measured carbon dioxide concentration remained stable even after long-term continuous operation and measurement. Therefore, it was found that by providing a desulfurization filter, the control of nutrient addition based on carbon dioxide concentration can be optimized over the long term.

[0042] [Reference examples 2~7] We investigated whether aerobic biological treatment can be controlled by using carbon dioxide concentration at least. First, we will describe the common test conditions for Reference Examples 2 to 7. A single-stage reaction vessel shown in Figure 2, with a volume of 19 L, was used to perform biological treatment of raw organic wastewater by aerobic treatment. Aerobic microorganisms were supported on a sponge carrier made of hydrophobic polyurethane resin, and this sponge carrier was filled into the reaction vessel at a bulk volume of 20% of the vessel's volume. The residence time in the reaction vessel was set to 18 hours. Isopropyl alcohol-containing wastewater was used as the raw water. The BOD concentration in the raw water was approximately 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 volumetric load during biological treatment was approximately 1 kg / m³ 3 The daily rate was as follows: water temperature was approximately 20°C, dissolved oxygen (DO) concentration in the water in the reaction vessel was 2 mg / L or higher, and the pH of the water in the reaction vessel was 6.0 to 7.5. Air was supplied to the reaction vessel at a flow rate of 3 to 5 L / min for aeration.

[0043] Nutrients (nitrogen (N) and phosphorus (P)) were added to the raw water to achieve a BOD:N:P ratio of 100:5:1, and the concentration of carbon dioxide released from the water in the reaction vessel and the pH of the water in the reaction vessel were monitored. This monitoring was repeatedly performed while intentionally changing the BOD concentration in the raw water from 100% of the standard concentration to 30% and 60%. It should be noted that the ability to calculate the BOD concentration of the raw water with high accuracy is equivalent to the high accuracy of nutrient addition control.

[0044] (Reference example 2) To calculate the BOD concentration of the raw water from the carbon dioxide concentration, the coefficient of determination R was obtained by performing a simple linear regression analysis on the carbon dioxide concentration and each BOD concentration. 2 The calculated value was 0.39.

[0045] (Reference example 3) The BOD concentration of the raw water is calculated from the carbon dioxide concentration and airflow rate, and the coefficient of determination R is calculated by multiple regression analysis of the carbon dioxide concentration, airflow rate and each BOD concentration. 2 The calculated value was 0.82.

[0046] (Reference example 4) To calculate the BOD concentration of raw water from carbon dioxide concentration and airflow rate, the product of the measured carbon dioxide concentration and measured airflow rate is determined, and the coefficient of determination R is calculated by performing a simple linear regression analysis on this product and each BOD concentration. 2 The calculated value was 0.83.

[0047] (Reference example 5) The BOD concentration of the raw water is calculated from the carbon dioxide concentration and pH, and the coefficient of determination R is calculated by multiple regression analysis on the carbon dioxide concentration, pH, and each BOD concentration. 2 The calculated value was 0.40.

[0048] (Reference example 6) The BOD concentration of the raw water is calculated from the carbon dioxide concentration, airflow rate, and pH. The coefficient of determination R is calculated by multiple regression analysis between the carbon dioxide concentration, airflow rate, pH, and each BOD concentration. 2The calculated value was 0.89.

[0049] (Reference example 7) The BOD concentration of the raw water is calculated from the carbon dioxide concentration, airflow rate, and pH. The product of the measured carbon dioxide concentration and the measured airflow rate is determined, and the coefficient of determination R is calculated by performing multiple regression analysis on this product, pH, and each BOD concentration. 2 The calculated value was 0.96. [Explanation of symbols]

[0050] 10 reaction vessels 11 Carrier 12 Air diffuser 13 Inlet piping 14 Gas Piping 15 Blower 16 Lid 21. Nutrient storage tank 22 Nutrient solution piping 23 pumps 31. Carbon dioxide concentration sensor 32 Air flow meter 33 Water quality measurement section 40 Control device 51 Tubular member 52 Desulfurization filter

Claims

1. A wastewater treatment method for carrying out aerobic biological treatment on organic wastewater containing at least one of sulfur compounds and nitrogen compounds in a reaction tank, comprising: removing corrosive gases from the gas released from the water in the reaction vessel; measuring a carbon dioxide concentration in the gas after removing the corrosive gas; A wastewater treatment method comprising controlling the aerobic biological treatment based on the measured carbon dioxide concentration.

2. The BOD treatment load in the reaction tank when the aerobic biological treatment is carried out is 1.5 kg / m ３ The wastewater treatment method according to claim 1, wherein the wastewater treatment time exceeds 100 minutes / day.

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

4. 3. The wastewater treatment method according to claim 1, wherein the aerobic biological treatment is carried out by forming a fluidized bed in the reaction tank.

5. 3. The wastewater treatment method according to claim 1, wherein, when a plurality of the reaction tanks are provided in series, the removal of the corrosive gas and the measurement of the carbon dioxide concentration are performed in a 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 reaction tank for performing aerobic biological treatment on organic wastewater containing at least one of sulfur compounds and nitrogen compounds; a removal means for removing corrosive gas from the gas released from the water in the reaction tank; a measuring means for measuring a carbon dioxide concentration contained in the gas after the corrosive gas has been removed; A control means for controlling the aerobic biological treatment based on the carbon dioxide concentration measured by the measurement means; A wastewater treatment device comprising:

7. The BOD treatment load in the reaction tank is 1.5 kg / m ３ The wastewater treatment device according to claim 6 , wherein the aerobic biological treatment is carried out under conditions in which the aerobic biological treatment time exceeds 100 s / day.

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

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

10. A plurality of the reaction vessels are provided in series, the removing means and the measuring means are provided for the first stage reaction vessel, The wastewater treatment equipment according to claim 6 or 7, wherein the control means controls the aerobic biological treatment in the first-stage reaction tank.

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