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 device for treating organic wastewater by aerobic biological treatment. [Background technology]

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

[0003] It is recommended that the amount of nutrients added to raw water, which is organic wastewater, be proportional to the organic matter concentration in the raw water. Assuming that the organic matter concentration in the raw water is expressed as biochemical oxygen demand (BOD), a preferred amount of added nutrients, nitrogen (N) and phosphorus (P), in wastewater treatment using aerobic microorganisms, i.e., aerobic biological treatment, is, for example, BOD:N:P=100:5:1 by mass. While 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, a 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 using an online TOC concentration meter, converted into a BOD value, and the amount of added nitrogen and phosphorus is controlled based on the obtained BOD value (see, for example, Patent Document 1).

[0004] When wastewater treatment is carried out using aerobic microorganisms, a fully aerobic condition is generally 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, sulfur components in organic wastewater are converted into sulfate ions (SO42- In contrast to aerobic biological treatment, biological treatment that uses anaerobic microorganisms is called anaerobic biological treatment. However, as described in Patent Document 2, it is known that anaerobic biological treatment, such as methane fermentation, generates corrosive gases such as hydrogen sulfide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-334285 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-81264 Summary of the Invention [Problem to be solved by the invention]

[0006] The method of controlling the amount of nutrients added based on the TOC concentration measured online has the problem that the inside of the piping of the online TOC concentration meter can become clogged due to the accumulation of suspended solids (SS), oil, and biofilm formation, making the measurements unstable and, as a result, making the biological treatment itself unstable.Similarly, when aerobic biological treatment is performed under conditions of high BOD volumetric load, the treatment can become unstable.

[0007] An object of the present invention is to provide a wastewater treatment method and wastewater treatment apparatus that can stably carry out aerobic biological treatment of organic wastewater. [Means for solving the problem]

[0008] The present inventors have discovered that when performing aerobic biological treatment of organic wastewater, the concentration of carbon dioxide generated from the water in the reaction tank can be measured, and the amount of nutrients to be added can be determined from the measured carbon dioxide concentration. Because the carbon dioxide concentration is measured in the gas phase, problems such as the accumulation of suspended matter and oil, and the formation of biofilms, which occur when measuring TOC concentrations, can be avoided. Furthermore, the present inventors have found that when biological treatment of organic wastewater containing sulfur compounds is performed under fully aerobic conditions, where the dissolved oxygen (DO) concentration in the water in the reaction tank is 3 mg / L or higher, if the volumetric load of organic matter in the biological treatment is large, for example, 1.5 kg / m 2 in terms of BOD volumetric load, the volumetric load of organic matter in the biological treatment can be reduced. 3 It was found that if the BOD volume load exceeds 1 / day, hydrogen sulfide, which is supposed to be a product of anaerobic treatment, may be generated. Hydrogen sulfide is harmful to the sensors used to measure carbon dioxide concentration. Similarly, if the organic wastewater contains nitrogen compounds, ammonia and other gases may be generated even when biological treatment is carried out under fully aerobic conditions if the BOD volume load is large. Ammonia is also considered a corrosive gas because it can have a negative effect on the wiring inside the sensor.

[0009] Therefore, the wastewater treatment method of the present invention is a wastewater treatment method in which aerobic biological treatment is carried out in a reaction tank on organic wastewater containing at least one of sulfur compounds and nitrogen compounds, 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 device 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 means that removes corrosive gases from gas released from the water in the reaction tank, a measurement means that measures the carbon dioxide concentration contained in the gas after the corrosive gases have been removed, and a control means that controls the aerobic biological treatment based on the carbon dioxide concentration measured by the measurement means.

[0011] As described above, even when biological treatment of organic wastewater is performed under fully aerobic conditions, if the volume load of organic matter in the biological treatment in the reactor is large, corrosive gases such as hydrogen sulfide and ammonia are generated. In the present invention, the corrosive gases contained in the gas generated from the reactor are removed before measuring the carbon dioxide concentration contained in the gas. This prevents adverse effects on sensors used to measure the carbon dioxide concentration, making it possible to stably control the aerobic biological treatment based on the carbon dioxide concentration when the aerobic biological treatment is performed. [Effects of the Invention]

[0012] According to the present invention, aerobic biological treatment can be stably carried out even when the volume load of organic matter in organic wastewater is large. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing a wastewater treatment device according to an embodiment of the present invention; [Figure 2] FIG. 10 is a diagram showing a wastewater treatment device according to another embodiment. [Figure 3] FIG. 10 is a diagram showing a wastewater treatment device according to still another embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0015] The present invention relates to a technology for biologically treating raw organic wastewater using aerobic microorganisms (i.e., aerobic biological treatment) to decompose and remove organic substances in the raw organic wastewater. The organic wastewater targeted by the present invention is not particularly limited as long as it is amenable to aerobic biological treatment, and includes, for example, wastewater discharged from public sewerage systems, food factories, chemical factories, semiconductor manufacturing factories, liquid crystal manufacturing factories, paper and pulp factories, and other industrial facilities. Compared with wastewater discharged from public sewerage systems, wastewater from private factories is more likely to lack the nutrients necessary to maintain high decomposition activity of the microorganisms used in biological treatment. This nutrient deficiency is particularly pronounced in wastewater from chemical factories, semiconductor manufacturing factories, and liquid crystal manufacturing factories. In the present invention, aerobic biological treatment is carried out using activated sludge, membrane bioreactor (MBR), a fluidized bed or fixed bed biofilm process, a granular process, or the like.

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

[0017] To optimize the amount of nutrients added to raw water, this embodiment does not directly measure the BOD or TOC concentrations of the raw water, but instead measures the carbon dioxide concentration in the gas released from the water in the reaction tank. This embodiment is based on aerobic biological treatment, which typically involves supplying oxygen-containing gas, such as air, to the reaction tank using a blower or other device to perform aeration or aeration on the water in the reaction tank. Therefore, it is preferable to measure the flow rate of the gas supplied to or released from the reaction tank along with the carbon dioxide concentration. The amount of nutrients added to the raw water is then controlled based on the measured carbon dioxide concentration or based on the measured carbon dioxide concentration and gas flow rate.

[0018] When control is performed based on the measured carbon dioxide concentration and the measured gas flow rate, the organic matter concentration in the raw water may be calculated from the measured carbon dioxide concentration and the measured flow rate, and the amount of nutrients added to the raw water may be controlled based on the calculated organic matter concentration. Alternatively, 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) in the reaction tank may be measured, and the amount of nutrients added to the raw water may be controlled based on the measured carbon dioxide concentration, the measured flow rate, and the measured water quality. The gas flow rate may be measured by measuring the flow rate of air supplied to the reaction tank from a blower, or by measuring the total flow rate of gas released from the reaction tank. When aerobic treatment is performed using a fluidized bed, a screen is placed in the reaction tank to separate the carriers, and air is also blown in to clean the screen. In this case, the gas flow rate may be the sum of the air volume of the blower for aeration and the air volume for cleaning the screen.

[0019] FIG. 1 shows a wastewater treatment system according to one embodiment of the present invention. The wastewater treatment system shown in FIG. 1 includes a fluidized-bed reactor 10 that stores raw organic wastewater and biologically treats the raw water under aerobic conditions. Treated water, from which organic matter has been decomposed and removed by biological treatment, is discharged from the reactor 10. The reactor 10 is filled with carriers 11, and an aeration device 12 is installed at the bottom of the reactor 10 to blow air into the reactor 10 for oxygen supply, i.e., aeration. An inlet pipe 13 is connected to the reactor 10, supplying raw water to the reactor 10. A gas pipe 14 is connected to the aeration device 12 to supply air to the aeration device 12, and the gas pipe 14 is equipped with an air blower 15. Examples of carriers 11 that can be used here include plastic carriers, sponge-like carriers, and gel-like carriers. Among these, sponge-like carriers are preferred from the standpoints of cost and durability. The reactor 10 may also be equipped with an agitator for agitating the carriers 11.

[0020] In biological treatment, nutrients are necessary for microorganisms to maintain high decomposition activity and grow. If nutrients are insufficient in the raw water, nutrients must be added to the raw water in the reaction tank 10 or upstream of the reaction tank 10. The wastewater treatment system shown in FIG. 1 is provided with a nutrient storage tank 21 for storing a nutrient solution (i.e., nutrient solution), and the nutrient storage tank 21 is connected to the inlet pipe 13 via a nutrient solution pipe 22. The nutrient solution pipe 22 is equipped with a pump 23 for feeding the nutrient solution. Therefore, in this wastewater treatment system, nutrients can be added to the raw water flowing through the inlet pipe 13 and 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 classified 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. As the phosphorus source, phosphoric acid or a phosphate can be used.

[0021] In the wastewater treatment system shown in FIG. 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 due to aerobic biological treatment and the flow rate of air supplied to the reaction tank 10 for aeration. To this end, the reaction tank 10 is equipped with a carbon dioxide concentration sensor 31 that measures the carbon dioxide concentration in the gas released from the water in the reaction tank 10, and an air flow meter 32 that measures the flow rate of air flowing through the gas piping 14 is installed between the blower 15 and the aeration device 12. Assuming that the reaction tank 10 is covered with a lid 16, the carbon dioxide concentration sensor 31 is installed in the gas phase of the reaction tank 10 or in a piping connected to this gas phase. To prevent condensation on the carbon dioxide concentration sensor 31, if the carbon dioxide concentration sensor 31 is installed in the piping, the piping should be insulated and a mist separator or air dryer may be installed immediately before 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 located above the water surface in the pipe. The carbon dioxide concentration sensor 31 can be, for example, an optical, electrochemical, or semiconductor type, but it is particularly preferable to use a sensor using non-dispersive infrared absorption (NDIR). The carbon dioxide concentration can be measured manually or online.

[0023] As will be apparent from the examples and comparative examples described later, even if the dissolved oxygen (DO) concentration of the water in the reaction tank 10 is 3 mg / L or more and the conditions are completely aerobic, when the BOD volume load of the aerobic biological treatment in the reaction tank 10 is large, for example, 1.5 kg / m 3When the CO2 concentration sensor 31 is damaged by the corrosive gas, it becomes difficult to obtain stable measurements and to properly control the amount of nutrients added. Therefore, in the wastewater treatment system shown in FIG. 1, a pretreatment process is performed to remove corrosive gases from the gas released from the water in the reaction tank 10 before measuring the carbon dioxide concentration with the CO2 concentration sensor 31. Common methods for removing hydrogen sulfide include contacting the gas with iron oxide to remove it as iron sulfide and absorbing it into an alkaline agent such as sodium hydroxide. However, because alkaline methods also absorb and remove carbon dioxide, the iron oxide method is preferred in this embodiment.

[0024] In the example shown in FIG. 1 , the raw water, which is organic wastewater, contains sulfur compounds that may generate hydrogen sulfide. Therefore, the carbon dioxide concentration sensor 31 is disposed inside a tubular member 51, and a desulfurization filter 52 is attached to one end of the tubular member 51. Gas flows in one direction within the tubular member 51, as indicated by the arrow in the figure, driven by a fan or air pump (not shown). 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 located inside the reaction tank 10. However, the tubular member 51 may be provided so as to penetrate the lid 16, allowing the gas measured by the carbon dioxide concentration sensor 31 to be discharged outside the reaction tank 10. The desulfurization filter 52 is a filter that removes hydrogen sulfide using iron oxide and is filled with, for example, a filler containing iron oxide. The filler may be, for example, granular or cylindrical with a diameter of 4 to 12 mm, or may be processed into a porous honeycomb shape. From the viewpoint of high treatment 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 said to be about that level.

[0025] Next, we will explain how to control the amount of nutrients added in the wastewater treatment system shown in Figure 1. It is recommended that the amount of nutrients (nutrients and trace metals) added to raw water be proportional to the organic matter concentration, preferably the BOD, of the raw water. For example, it is recommended that the amount of nitrogen (N) and phosphorus (P) added in aerobic treatment be a BOD:N:P ratio of 100:5:1 by mass. In the wastewater treatment system shown in Figure 1, the BOD of the raw water is not measured using an online TOC concentration meter or the like. Instead, the system measures the carbon dioxide concentration in the gas released from the water in the reaction tank 10 during aerobic biological treatment and the flow rate (i.e., air volume) of air supplied to the reaction tank 10 for aeration. The BOD value of the raw water is then calculated from the measured carbon dioxide concentration and air flow rate, and the amount of nutrients 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 air volume obtained by the air volume meter 32 is set as the input value (Xn), the BOD concentration of the raw water corresponding to the input value (Xn) is set as the output value (Yn), and a certain number of combinations of input and output values ​​(for example, several tens to a hundred sets) are acquired in advance, and then a model (or relational equation) is created. In this case, instead of using the combination of the carbon dioxide concentration and the measured air volume as the input value (Xn), the value obtained by multiplying the measured carbon dioxide concentration by the measured air volume (i.e., the multiplied value) may be used as the input value (Xn). In the case of the multiplied value method, if the air volume is constant, it is also possible to use only the measured carbon dioxide concentration instead of the multiplied value.

[0026] Once the model is created, a combination of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 and the air volume measured by the air volume meter 32 is input into the model, and the resulting BOD concentration value output from the model is used to drive the pump 23 and control whether or not to add nutrients to the raw water, and the amount of nutrients to be added. To achieve this control, the wastewater treatment device is equipped with a control device 40 that stores the created model, applies the carbon dioxide concentration value obtained by the carbon dioxide concentration sensor 31 and the measurement value obtained by the air volume meter 32 to the model to calculate the BOD concentration value of the raw water, and starts and stops the pump 23 and controls the flow rate based on the BOD concentration value. Although the model uses BOD concentration to create the model, the created model itself can be thought of as inputting the measured carbon dioxide concentration and air volume and directly outputting the amount of nutrients to be added. Therefore, once the model is created, the optimal amount of nutrients to be added can be determined without explicitly calculating the BOD concentration value from the measured carbon dioxide concentration and air volume.

[0027] Next, we will explain how to create a model. A model that outputs the BOD concentration of raw water corresponding to an input value can be created using, for example, various regression analyses. In particular, creating a model through supervised learning using neural network technology improves the accuracy of controlling the amount of nutrient addition. The carbon dioxide concentration measured by the carbon dioxide concentration sensor 31 may vary depending on the configuration and size of the reaction tank 10, the size of the gas phase in the reaction tank 10, the type of biological treatment, and the like. Furthermore, the air volume supplied to the reaction tank 10 for aeration also varies depending on the configuration and size of the reaction tank 10. Therefore, a model may be created for each reaction tank 10. Furthermore, since the relationship between the BOD of raw water and the measured carbon dioxide concentration and air volume may vary depending on the type or source of raw water, a model may be prepared for each type or source of raw water, and a model to be used for controlling the amount of nutrient addition may be selected from the prepared models depending on the type and source of raw water.

[0028] In the wastewater treatment device shown in FIG. 1 , an air flow meter 32 is provided in the gas pipe 14 to measure the flow rate of air supplied to the reaction tank 10, i.e., the air volume, via the gas pipe 14. However, instead of measuring the flow rate of air supplied to the reaction tank 10, the flow rate of gas released from the reaction tank 10 may be measured. When measuring the flow rate of gas released from the reaction tank 10, if the reaction tank 10 is completely covered with the lid 16, the air flow meter 32 may be installed in a pipe that communicates with the interior of the reaction tank 10 for discharging the gas to the outside. If the reaction tank 10 is an open system, in order to reduce the influence of outside air on the measurement results, the open area at the top of the reaction tank 10 can be made as small as possible, and a cylindrical pipe or the like can be inserted below the water surface, and the air flow meter 32 can be installed in that pipe.

[0029] To control the amount of nutrients added to raw water, it is possible to measure the organic matter concentration in the raw water online using an online TOC meter. However, online TOC meters require thin piping to draw a small amount of sample water into the measuring device, which is prone to clogging and unstable measurements. In contrast, the carbon dioxide concentration sensor 31 measures without contact with the water, resulting in extremely stable measurements. It also provides stable gas flow rate measurements. Therefore, the wastewater treatment system shown in Figure 1 makes it possible to stably determine the optimal amount of nutrients to be added to raw water without directly measuring the organic matter concentration in the raw water.

[0030] FIG. 2 shows a wastewater treatment device according to another embodiment of the present invention. The wastewater treatment device shown in FIG. 2 differs from the wastewater treatment device shown in FIG. 1 in that it includes a water quality measurement unit 33 that measures the water quality in the reaction tank 10, and the measurement results from the water quality measurement unit 33 are also sent to the control device 40. The water quality parameters measured by the water quality measurement unit 33 include at least pH, and other parameters such as water temperature may also be measured. The model used in the wastewater treatment device shown in FIG. 2 uses a combination of the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31, the air volume measurement obtained by the air volume meter 32, and the water quality (particularly pH) measurement by the water quality measurement unit 33 as input (Xn), and the BOD concentration of the raw water corresponding to the input value (Xn) as output value (Yn). This model is created in a similar manner to the model described above. The control device 40 applies the carbon dioxide concentration measured by the carbon dioxide concentration sensor 31, the air volume measurement obtained by the air volume meter 32, and the water quality (particularly pH) measurement 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.

[0031] As is well known, inorganic carbonic acid in water is converted into CO2 and HCO3 depending on the pH. - , CO3 2- The form of the nutrients changes depending on the pH. Therefore, even if the organic matter concentration in the raw water is the same, the carbon dioxide concentration in the gas released from the water in the reaction tank 10 may change depending on the pH. In the wastewater treatment device shown in FIG. 2, the amount of nutrients added is controlled taking into account the pH of the water in the reaction tank 10, so the amount of nutrients added can be optimized regardless of the pH of the raw water. Furthermore, the solubility of carbon dioxide in water depends on the water temperature, and if the solubility of carbon dioxide changes, the carbon dioxide concentration in the gas released from the water in the reaction tank 10 also changes. Therefore, if the water temperature in the reaction tank 10 fluctuates, 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, air flow, and pH.

[0032] In wastewater treatment, multiple biological reactors are connected in series, and treated water discharged from the first reactor is introduced into the next reactor, where it undergoes biological treatment, resulting in treated water with a high degree of organic matter removal. Figure 3 shows a wastewater treatment system similar to those shown in Figures 1 and 2, which uses aerobic biological treatment, with multiple reactors 10 connected in series, i.e., in multiple stages. When two or more reactors 10 are connected in multiple stages, the carbon dioxide concentration in the gas released from the first reactor 10 and the airflow rate are measured. The BOD concentration of the raw water is calculated from the carbon dioxide concentration and airflow rate. Based on the BOD concentration, the amount of nutrients added to the raw water supplied to that reactor can be controlled. In this case, the pH of the water in the first reactor 10 can also be measured, and the amount of nutrients added to the raw water can be controlled based on the carbon dioxide concentration, airflow rate, and pH. 3, the carbon dioxide concentration sensor 31, air flow meter 32, and water quality measurement unit 33 are provided only in the first-stage reaction tank 10, and nutrient solution from the nutrient storage tank 21 is added to raw water in the inlet pipe 13 connected to the first-stage reaction tank 10. The carbon dioxide concentration sensor 31 is provided inside a tubular member 51, one end of which is equipped with a desulfurization filter 52, as in the device shown in FIG. 1. The control device 40 calculates the BOD concentration value of the raw water from the measurements of the carbon dioxide concentration sensor 31, air flow meter 32, and water quality measurement unit 33, and controls the pump 23 that supplies the nutrient solution based on the BOD concentration value.

[0033] When two or more reactors 10 are arranged in series, most of the organic matter is decomposed and removed in the first reactor 10, reducing the amount of organic matter that must be removed in the second and subsequent reactors 10. Additionally, as the microorganisms that proliferated in the first reactor 10 die and disintegrate, nutrients are re-eluted. For these reasons, biological treatment can proceed in the second and subsequent reactors 10 without adding nutrients to the water supplied to the second and subsequent reactors 10 or without special control of the biological treatment in the second and subsequent reactors 10, thereby maintaining the overall treatment performance of the wastewater treatment system. Therefore, measurements of carbon dioxide concentration, air volume, and pH are not required for the second and subsequent reactors. [Example]

[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 and 2] First, the test conditions common to Example 1, Reference Example 1, and Comparative Examples 1 and 2 will be explained. A wastewater treatment device was constructed by preparing a reaction tank for 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 sponge carriers made of hydrophobic polyurethane so that the filling rate was 20% in terms of bulk volume. Wastewater containing isopropyl alcohol was prepared as organic wastewater. The BOD concentration of the wastewater was 180 to 330 mg / L, the nitrogen (N) concentration was 10 to 26 mg / L, the phosphorus (P) concentration was 0.5 mg / L or less, and the sulfate ion (SO4 2- The concentration of nitrites in the wastewater was 60-360 mg / L. This wastewater was supplied to a reactor, where aeration was performed and nutrients were added, for aerobic biological treatment. Phosphate and trace metals were used as nutrients. The water temperature was approximately 30°C, the pH of the water in the reactor was 6.5-7.0, and the dissolved oxygen concentration was 3 mg / L or higher, satisfying the fully aerobic conditions.

[0036] To measure the carbon dioxide concentration of the gas released from the water in the reaction tank, a pipe communicating with the gas phase of the reaction tank was installed. Gas was extracted from this pipe using an air pump, and the carbon dioxide concentration of the extracted gas was continuously measured using a carbon dioxide concentration sensor. The carbon dioxide concentration sensor was a non-dispersive infrared (NDIR) sensor. This carbon dioxide concentration sensor attached to the reaction tank will be referred to as the control sensor. In Example 1, the gas extracted from the pipe was passed through a column packed with a honeycomb-shaped packing material coated with iron oxide in an upward flow manner, and the carbon dioxide concentration of the gas was measured using the control sensor. This column corresponds to a desulfurization filter. On the other hand, in Comparative Examples 1 and 2 and Reference Example 1, a desulfurization filter was not installed, and the carbon dioxide concentration of the gas extracted from the pipe was directly measured using the control sensor.

[0037] Example 1 The BOD volume load of the aerobic biological treatment in the reactor is set at 4 kg / m 3 The wastewater treatment equipment was continuously operated for 10 min / day, and after pretreatment using a desulfurization filter, continuous measurement of the carbon dioxide concentration was performed using a control sensor. Approximately three months after the start of operation, gas generated from the water in the reaction tank was sampled, and the carbon dioxide concentration in this gas (referred to as the standard gas concentration) was measured using a measuring device different from the control sensor, and compared with the measurement value obtained by the control sensor at that time. As a result, the measurement value obtained by the control sensor was 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 by the control sensor was within the allowable range.

[0038] (Comparative Example 1) The same procedure as in Example 1 was carried out except that the carbon dioxide concentration was measured using a control sensor without installing a desulfurization filter, and the BOD volume load was 4 kg / m 3The wastewater treatment equipment was operated continuously under the condition of 1000ppm / day, and the carbon dioxide concentration was also measured continuously. As a result, about three months after the start of operation, a sensor error occurred in the control sensor, and the carbon dioxide concentration could no longer be measured. At this time, the hydrogen sulfide concentration in the gas generated from the reaction tank was measured and was found to be over 0.7 ppm.

[0039] (Comparative Example 2) BOD volumetric load: 3 kg / m 3 The wastewater treatment equipment was continuously operated in the same manner as in Comparative Example 1, except that the treatment time was set to 1 / 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 140% of the standard gas concentration, indicating a large measurement error. At this time, hydrogen sulfide was also detected in the gas generated from the reaction tank.

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

[0041] From Reference Example 1 and Comparative Examples 1 and 2, it was found that even if the dissolved oxygen concentration of the water in the reaction tank was set to 3 mg / L or more under completely aerobic conditions, the BOD load capacity was 1.5 kg / m 3When the nitrate concentration exceeds 1 / day, hydrogen sulfide, which would normally only be generated under anaerobic conditions, is generated from the reaction tank. It was also found that this hydrogen sulfide adversely affects the carbon dioxide concentration sensor. After approximately three months of continuous operation and measurement, the carbon dioxide concentration sensor became unable to measure or exhibited significant measurement errors. In contrast, in Example 1, in which hydrogen sulfide is removed using a desulfurization filter before measuring the carbon dioxide concentration, even under similar conditions where hydrogen sulfide is generated, the measured carbon dioxide concentration remained stable even after long-term continuous operation and measurement. Therefore, it was found that the installation of a desulfurization filter allows for long-term optimization of the control of nutrient addition based on carbon dioxide concentration.

[0042] [Reference examples 2~7] We investigated whether aerobic biological treatment can be controlled by using at least carbon dioxide concentration. First, the test conditions common to Reference Examples 2 to 7 are explained. A single-stage reaction tank with a volume of 19 L as shown in Figure 2 was used to carry out aerobic biological treatment of raw water, which was organic wastewater. Aerobic microorganisms were supported on sponge carriers made of hydrophobic polyurethane resin, and these sponge carriers were filled into the reaction tank at a bulk volume of 20% of the volume of the reaction tank. The retention time in the reaction tank was 18 hours. Wastewater containing isopropyl alcohol was used as the raw water. The BOD concentration in the raw water was 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 volume load during biological treatment was approximately 1 kg / m 3 The water temperature was approximately 20°C, the dissolved oxygen concentration (DO) of the water in the reaction tank was 2 mg / L or more, and the pH of the water in the reaction tank was 6.0 to 7.5. Air was supplied to the reaction tank at a flow rate of 3 to 5 L / min for aeration.

[0043] Sufficient 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 tank and the pH of the water in the reaction tank were monitored. This monitoring was repeated while intentionally changing the BOD concentration in the raw water from 100% of the standard concentration to 30% and 60%. Note that being able to calculate the BOD concentration of the raw water with high accuracy is equivalent to having high accuracy in nutrient addition control.

[0044] (Reference example 2) The BOD concentration of raw water was calculated from the carbon dioxide concentration, and the coefficient of determination R was calculated by simple regression analysis for the carbon dioxide concentration and each BOD concentration. 2 was calculated to be 0.39.

[0045] (Reference example 3) The BOD concentration of raw water was calculated from the carbon dioxide concentration and air volume, and the coefficient of determination R was calculated by multiple regression analysis for the carbon dioxide concentration, air volume, and each BOD concentration. 2 was calculated to be 0.82.

[0046] (Reference example 4) The BOD concentration of raw water is calculated from the carbon dioxide concentration and air volume. The measured carbon dioxide concentration is multiplied by the measured air volume, and the coefficient of determination R is calculated by simple regression analysis between this multiplication and each BOD concentration. 2 was calculated to be 0.83.

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

[0048] (Reference example 6) The BOD concentration of raw water was calculated from the carbon dioxide concentration, air volume, and pH. The coefficient of determination R was calculated by multiple regression analysis for the carbon dioxide concentration, air volume, pH, and each BOD concentration. 2was calculated to be 0.89.

[0049] (Reference example 7) The BOD concentration of raw water is calculated from the carbon dioxide concentration, air volume, and pH. The measured carbon dioxide concentration is multiplied by the measured air volume, and the coefficient of determination R is calculated by multiple regression analysis for this multiplication, pH, and each BOD concentration. 2 was calculated to be 0.96. [Explanation of symbols]

[0050] 10 Reaction vessel 11 Carrier 12 Air diffuser 13 Inlet piping 14 Gas piping 15 Blower 16 Lid 21 Nutrient storage tank 22 Nutrient solution piping 23 Pump 31 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 performing 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 the 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 the concentration of carbon dioxide 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 having the above structure.

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 device 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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