Measuring apparatus and measuring method

Abstract

To provide a measuring device capable of accurately measuring the amount of dissolved nitrogen gas excessively dissolved in sewage in an activated sludge tank.SOLUTION: The measuring apparatus 10 is provided with a collecting vessel 20 for collecting waste water, an ultrasonic oscillator 1 for transmitting ultrasonic waves to the waste water in the collecting vessel 20, and a collecting vessel 4 for collecting gaseous nitrogen generated in the collecting vessel 20, and the collecting vessel 20 is provided with a storage vessel 21a made of a soft resinous material and an opening / closing mechanism 22 for switching the collecting vessel 20 between an open state and a closed state. Only nitrogen gas excessively dissolved in wastewater containing activated sludge in excess of a saturation amount is degassed by irradiating the wastewater in a collection container 20 with ultrasonic waves from an ultrasonic oscillator 1 and the degassed nitrogen gas is transferred to a collection container 4 to measure the concentration of degassed nitrogen.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a measuring device and a measuring method for measuring the amount of nitrogen gas dissolved in water. [Background technology]

[0002] Conventionally, water treatment systems have been used that include a grit basin that removes large debris and sand from sewage, a primary sedimentation basin that removes small debris and sand from the sewage that has passed through the grit basin, an activated sludge tank in which activated sludge, which is made up of microorganisms or bacteria, adsorbs, oxidizes, or coagulates dissolved organic matter, nitrogen compounds, and phosphorus compounds contained in the sewage that has passed through the primary sedimentation basin to treat the sewage, and a final sedimentation basin in which activated sludge from the activated sludge tank is allowed to settle and separate. The activated sludge tank has an aeration device that aerates air as an oxygen-containing gas (see, for example, Patent Document 1). The aeration device in Patent Document 1 is installed at the bottom of the activated sludge tank and aerates air containing oxygen and nitrogen toward the surface of the sewage being supplied to the activated sludge tank, and the oxygen and nitrogen aerated from the aeration device dissolve in the sewage.

[0003] The pressure of sewage supplied to the activated sludge tank increases with increasing water depth, and the amount of gaseous material dissolved in sewage is proportional to the pressure under certain conditions. Therefore, the solubility of oxygen and nitrogen contained in aerated air in sewage increases with increasing water depth. In other words, the solubility of oxygen and nitrogen contained in aerated air in sewage varies depending on the water pressure of the sewage, which depends on the water depth. The oxygen contained in aerated air is consumed by activated sludge after dissolving in sewage, but the nitrogen contained in aerated air (hereinafter referred to as "dissolved nitrogen gas") is inert to sewage and activated sludge. Therefore, for example, dissolved nitrogen gas that enters the activated sludge after dissolving in sewage is retained in the activated sludge or discharged from the activated sludge.

[0004] Incidentally, a dissolved gas concentration measuring device that measures the concentration of a predetermined gas dissolved in tap water is known (see, for example, Patent Document 2). The dissolved gas concentration measuring device of Patent Document 2 includes, for example, a container that holds tap water with dissolved oxygen and a U-shaped tube in which a liquid is sealed. When the container is shaken, the oxygen that was initially dissolved in the tap water becomes unable to dissolve in the tap water, and gaseous oxygen is generated. The liquid sealed in the U-shaped tube is displaced based on the generated oxygen, and the amount of oxygen dissolved in the tap water (dissolved oxygen amount) is obtained based on the displacement of the liquid sealed in the U-shaped tube. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-118184 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-215282 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when sewage treated with activated sludge and containing activated sludge is transferred from the activated sludge tank to the final settling tank, for example, if the water depth of the activated sludge tank is deeper than that of the final settling tank, the solubility of nitrogen in the activated sludge tank may be greater than that in the final settling tank. In this case, some of the dissolved nitrogen gas in the sewage cannot be dissolved in the sewage, and nitrogen is generated as bubbles. The bubbles move toward the surface of the sewage in the final settling tank, and the activated sludge rises to the surface along with the movement of the bubbles. Therefore, the activated sludge does not settle and separate from the sewage in the final settling tank.

[0007] To address this issue, even if the solubility of nitrogen decreases as sewage is transferred from the activated sludge tank to the final settling tank, it is necessary to adjust the air conditions in the activated sludge tank so that nitrogen bubbles do not form in the final settling tank and the activated sludge does not float. In other words, the amount of dissolved nitrogen gas in the sewage in the activated sludge tank (hereinafter referred to as "dissolved nitrogen gas amount") must be controlled based on the solubility in the final settling tank. However, there was a problem in that the amount of dissolved nitrogen gas dissolved in the sewage in the activated sludge tank in excess of the solubility in the final settling tank could not be accurately measured. As a result, the amount of dissolved nitrogen gas in the activated sludge tank could not be determined, and it was therefore impossible to determine the amount of reduction in the aeration rate in the activated sludge tank.

[0008] An object of the present invention is to provide a measuring device and a measuring method that can accurately measure the amount of dissolved nitrogen gas in excess in sewage in an activated sludge tank. [Means for solving the problem]

[0009] In order to achieve the above object, the measuring device of the present invention is a measuring device for measuring the amount of nitrogen gas dissolved in excess in wastewater containing activated sludge, and is characterized by comprising a collection means for collecting the wastewater, an ultrasonic generating means for generating ultrasonic waves to be transmitted to the collection means, and a collection means for collecting gas generated in the wastewater collected in the collection means.

[0010] In order to achieve the above-mentioned object, the measurement method of the present invention is a method for measuring the amount of nitrogen gas dissolved in excess in wastewater containing activated sludge using a measurement device having a collection means for collecting the wastewater, and is characterized by comprising a collection step for collecting the wastewater, an ultrasonic generation step for generating ultrasonic waves to be transmitted to the collection means, and a collection step for collecting gas generated in the wastewater collected in the collection means. [Effects of the Invention]

[0011] According to the present invention, the amount of dissolved nitrogen gas that is dissolved in excess in the sewage in the activated sludge tank can be measured with high accuracy. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing an apparatus for measuring the amount of dissolved nitrogen gas according to an embodiment of the present invention. [Figure 2] 2A and 2B are diagrams used to explain the measurement process of the amount of dissolved nitrogen gas performed by the measurement device of FIG. 1, where FIG. 2(A) is a diagram showing the operation of transmitting ultrasonic waves to the wastewater inside the collection container to degas the dissolved nitrogen gas that is dissolved in excess in the wastewater, FIG. 2(B) is a diagram showing the operation of transferring the nitrogen gas present inside the collection container to a collection container, and FIG. 2(C) is a diagram showing the operation of measuring the volume of nitrogen gas collected in the collection container. [Figure 3] 3A and 3B are schematic diagrams showing a collection container (closed state) provided in the measurement device of FIG. 1, where FIG. 3A is a front view of the collection container (closed state), FIG. 3B is a cross-sectional view of the collection container (closed state), and FIG. 3C is a perspective view showing the state in which the collection container (closed state) contains wastewater. [Figure 4] 3 is a flowchart showing the procedure of a process for measuring the amount of dissolved nitrogen gas executed by the measurement device of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0014] FIG. 1 is a diagram schematically illustrating an apparatus 10 for measuring the amount of dissolved nitrogen gas according to an embodiment of the present invention.

[0015] 1 includes a collection vessel 20 (collection means) that collects and stores wastewater containing activated sludge, an ultrasonic oscillator 1 (ultrasonic wave generating means) that transmits ultrasonic waves to the wastewater inside the collection vessel 20, and a collection vessel 4 (collection means) that collects nitrogen gas bubbles generated inside the collection vessel 20. The ultrasonic oscillator 1 includes a tank having a water bath inside, an oscillator 2 that supplies high-frequency power to an oscillator 3, the oscillator 3 that generates ultrasonic waves, and a heater mechanism (not shown).

[0016] 2A and 2B are diagrams used to explain the measurement process of the amount of dissolved nitrogen gas executed by the measurement device 10 of Fig. 1, in which Fig. 2A is a diagram showing an operation of transmitting ultrasonic waves to the wastewater inside the collection container 20 to degas the dissolved nitrogen gas dissolved in excess in the wastewater, Fig. 2B is a diagram showing an operation of transferring the nitrogen gas bubbles present inside the collection container 20 to the collection container 4, and Fig. 2C is a diagram showing an operation of measuring the weight of the nitrogen gas collected in the collection container 4. In the present invention, degassing refers to turning the dissolved nitrogen gas dissolved in excess in the wastewater inside the collection container 20 into bubbles.

[0017] In an embodiment of the present invention, first, wastewater collected from an activated sludge tank is placed in collection container 20, and the sealed collection container 20 is immersed in a water bath of ultrasonic oscillator 1. Next, ultrasonic waves are transmitted from transducer 3 of ultrasonic oscillator 1 to the wastewater inside collection container 20, thereby degassing excess dissolved nitrogen gas in the wastewater inside collection container 20 (FIG. 2(A)). Nitrogen gas bubbles generated inside collection container 20 are transferred to collection container 4 (FIG. 2(B)), and the volume of the nitrogen gas bubbles transferred to collection container 4 is measured gravimetrically using weighing device 5 (FIG. 2(C)).

[0018] 3A and 3B are schematic diagrams showing the collection container 20 (closed state) provided in the measurement device 10 of FIG. 1, where FIG. 3A is a front view of the collection container 20 (closed state), FIG. 3B is a cross-sectional view of the collection container 20 (closed state), and FIG. 3C is a perspective view showing the state in which the collection container 20 (closed state) contains wastewater.

[0019] In Figure 3, the collection vessel 20 is composed of a storage section 21 that stores wastewater collected from the activated sludge tank, an opening / closing mechanism 22 that switches the collection vessel 20 between an open state and a closed state, a connecting pipe 23 that connects the storage section 21 and the opening / closing mechanism 22, and a holding section 24 that holds the connecting pipe 23 and connects the connecting pipe 23 to the storage section 21. The storage section 21 is composed of a storage vessel 21a that stores wastewater and an opening 21b formed in the upper part of the storage vessel 21a that can be connected to the holding section 24 (Figure 3). The storage vessel 21a is, for example, a bag-like container that is approximately rectangular or approximately square and is made of a soft resin material. On the other hand, the opening 21b is made of a hard resin material so that it can be connected to the holding section 24.

[0020] In this embodiment, when ultrasonic waves are applied to the wastewater in the storage unit 21 using the ultrasonic oscillator 1, the dissolved nitrogen gas that is dissolved in the wastewater in excess of the saturation level is degassed inside the storage unit 21 (FIGS. 2(A) and 3). To measure the amount of degassed nitrogen gas, the nitrogen gas generated inside the storage unit 21 is transferred from the opening 21b through the connecting pipe 23 and the opening / closing mechanism 22 to the collection container 4 (FIGS. 2(B) and 3). Since the storage container 21a is made of a soft resin material, nitrogen gas bubbles in the wastewater can be easily transferred from the opening 21b toward the opening / closing mechanism 22 by pressing the wastewater from the outside of the storage container 21a. The resin material for the storage container 21a may be any material that allows the ultrasonic waves applied from the ultrasonic oscillator 1 to pass through and reach the wastewater inside. However, a colorless and transparent resin material is preferred to make it easier to check the nitrogen gas bubbles generated inside the storage unit 21.

[0021] In FIG. 2A, ultrasonic waves generated from the transducer 3 of the ultrasonic oscillator 1 pass through different media in the following order: the water in the water bath inside the ultrasonic oscillator 1, the resin material of the storage container 21a, and the water inside the storage container 21a. Each medium has a specific acoustic impedance, which indicates the ease of sound propagation. Here, acoustic impedance is a value obtained by multiplying the density of the medium by the speed of sound in the medium. When ultrasonic waves enter different media, due to differences in the specific acoustic impedances of the media, part of the incident wave is reflected at the interface between the different media, while the rest is transmitted. In this embodiment, ultrasonic waves generated from the transducer 3 of the ultrasonic oscillator 1 pass through the resin material of the storage container 21a and reach the wastewater inside the storage container 21a. However, the resin material of the storage container 21a must transmit ultrasonic waves sufficiently to completely degas the dissolved nitrogen gas that has dissolved in the wastewater inside the storage container 21a beyond the saturation amount. Therefore, it is preferable that the resin material has an ultrasonic reflectance RI at the interface between the resin material and water of 0.2 or less, preferably 0.15 or less, and more preferably 0.1 or less. The lower limit of the reflectance RI is not particularly limited, but is usually 0.01 or more.

[0022] In this embodiment, the reflectance RI of ultrasonic waves at the interface between the resin material and water is calculated by the following formula (1).

[0023] Reflectance RI=(z1-z2) 2 / (z1+z2) 2 ···(1)

[0024] In equation (1), z1 is the acoustic impedance value of the resin material (25°C), z2 is the acoustic impedance value of water (1.50 × 10 6 kg / m 2 In equation (1), the acoustic impedance value z1 of the resin material is set to a value at 25°C, taking into account the temperature of the wastewater in the activated sludge tank, and the acoustic impedance value z2 of water is set to 1.50 × 10 6 kg / m 2sec. When the difference in acoustic impedance between different media through which ultrasonic waves pass is large, the reflectance RI of the ultrasonic waves becomes large. On the other hand, when the difference in acoustic impedance between different media is small, the reflectance RI of the ultrasonic waves becomes small and transmission becomes large. Therefore, in this embodiment, it is preferable that the resin material forming the container 21a is a resin material having an acoustic impedance close to that of water. For example, when the acoustic impedance (at 25°C) of the resin material forming the container 21a is close to that of water (1.50×10 6 kg / m 2 sec) is 0.3 × 10 6 ~2.5×10 6 kg / m 2 sec, preferably 0.5×10 6 ~1.0×10 6 kg / m 2 sec.

[0025] In the above equation (1), z1 (the acoustic impedance value of the resin material) is calculated by measuring the density of the resin material and the sound velocity in the resin material maintained at 25°C, and multiplying the measured sound velocity by the density, with reference to the method described by Hisamoto et al. in "Study on a Method for Observing the Cross Section of a Limb Using an Ultrasonic Echo Method Combined with a Water Tank" (Journal of the Society of Biomechanisms, 2010, Vol. 34, No. 1, pp. 68-72). Specifically, the sound velocity in the resin material was measured by cutting a commercially available 5 mm thick resin material into a square with sides of 150 mm to prepare a test piece. The test piece was maintained at 25°C and measured using a pulse-echo sonic velocimeter (ECHOMETER 1075, manufactured by Carl Deutsche GmbH). The reflectance calculated by Hisamoto et al. is the reflectance at 10°C and 40°C (Journal of the Society of Biomechanisms, 2010, Vol. 34, No. 1, p. 69, Table 1), and can be used to calculate the reflectance RI (25°C) of the resin material of the container 21a in this embodiment. In other words, by taking the average of the reflectance when the resin material is at 10°C and the reflectance when the resin material is at 40°C in the calculation method of Hisamoto et al., the reflectance RI when the resin material is at 25°C in this embodiment can be obtained.

[0026] Resin materials having a reflectance RI of 0.2 or less include, but are not limited to, acrylic resin (reflectance at 25°C: 0.16), rigid polyvinyl chloride resin (0.12), polyethylene terephthalate (0.11), polycarbonate resin (0.08), polyacetal (0.13), ABS resin (0.04), polypropylene (0.05), high-density polyethylene (0.03), polyamide resin (0.11), and composite resin materials containing these. By using two or more of the above resin materials, the storage container 21a may be formed to have a multilayer film structure, such as a two-layer film structure, which has excellent sealing properties and pressure resistance.

[0027] Returning to FIG. 3, wastewater containing activated sludge collected from the activated sludge tank is poured into the storage vessel 21a through the opening 21b at the top of the storage section 21 from which the holding section 24 has been removed. The holding section 24, connecting pipe 23, and opening / closing mechanism 24 are then connected to the storage section 21 into which the wastewater has been poured. After expelling any air bubbles trapped inside the storage vessel 21a, the opening / closing mechanism 24 is closed to seal the collection vessel 20. The sealed collection vessel 20 is then immersed in a water bath inside the ultrasonic oscillator 1 for ultrasonic treatment, which will be described later (FIG. 2(A)). Therefore, the storage vessel 21a may be shaped so that it can stand upright in the water bath inside the ultrasonic oscillator 1; for example, the bottom of the storage vessel 21a may have a gusset. The volume of the storage vessel 21a is typically 300 to 1000 ml, but this is determined taking into account the volume of the collection vessel 4, which will be described later and which collects the nitrogen gas generated by ultrasonic treatment.

[0028] The opening / closing mechanism 22 is, for example, an opening / closing valve such as a two-way cock, which can switch the trapping container 20 between an open state and a closed state (FIG. 3). When the opening / closing mechanism 22 is in the closed state, the trapping container 20 is sealed, preventing water and air from entering the inside of the trapping container 20 from the outside and preventing wastewater and air bubbles from being discharged to the outside. In this embodiment, ultrasonic waves are applied to the wastewater inside the storage unit 21 from the ultrasonic oscillator 1, thereby degassing dissolved nitrogen gas that has dissolved in the wastewater in excess of the saturation amount. At this time, by applying ultrasonic waves with the opening / closing mechanism 22 in the closed state, the nitrogen gas degassed inside the storage unit 21 can be reliably retained inside the trapping container 20, allowing the amount of nitrogen gas to be accurately measured (FIG. 2(A)).

[0029] On the other hand, when the opening / closing mechanism 22 is in the open state, the wastewater inside the storage container 21a can be pushed from the outside to discharge the air or bubbles inside the collection container 20 to the outside through the opening / closing mechanism 22. When measuring the amount of nitrogen gas degassed by ultrasonic irradiation at this time, the collection container 4 described below is connected to the top of the opening / closing mechanism 22 in a water bath, taking care not to mix in any bubbles, and the nitrogen gas inside the collection container 20 is transferred to the collection container 4 (FIG. 2(B)).

[0030] In FIG. 3 , the connection section connecting the storage section 21 and the opening / closing mechanism 22 is composed of a connecting pipe 23 and a holding section 24 that holds the connecting pipe 23 and connects the connecting pipe 23 to the storage section 21. The connecting pipe 23 is connected to the opening 21b at the top of the storage section 21 via the holding section 24 and is also connected to the opening / closing mechanism 22. The connecting pipe 23 is a tube made of, for example, glass or a resin material, and typically has an inner diameter of 0.2 to 2 cm. Nitrogen gas bubbles generated inside the storage section 21 pass through the connecting pipe 23 as they move to the collection container 4. At this time, it is important that nitrogen gas bubbles are not trapped inside the connecting pipe 23. Therefore, it is preferable that the inner surface of the connecting pipe 23 has a shape with few irregularities or corrugations that would trap bubbles. The holding section 24 has a hole through which the connecting pipe 23 passes and holds the connecting pipe 23 in a sealed state, and is, for example, a silicone plug that can be sealed and connected to the opening 21b at the top of the storage section 21.

[0031] 1, ultrasonic oscillator 1 comprises a tank having a size sufficient to immerse collection container 20 in a water bath, oscillator 2 that generates high-frequency power and supplies it to oscillator 3, oscillator 3 that converts the high-frequency power supplied from oscillator 2 into vibrations to generate ultrasonic waves, and a heater mechanism (not shown) that maintains the temperature of the water bath constant. Ultrasonic oscillator 1 has a water bath inside the tank, and transmits ultrasonic waves from oscillator 3 to the wastewater inside collection container 20 while collection container 20, which is sealed and contains wastewater, is immersed in the water bath.

[0032] The vibrator may be either an electrostrictive or magnetostrictive vibrator, but an electrostrictive bolt-clamped Langevin vibrator (BL vibrator) that operates at a relatively low frequency is preferred, and vibrators that are directly bonded to the bottom or side of the tank, immersion vibrators that are submerged in the tank, vibrators that are integrated with the tank and oscillator, etc. A commercially available ultrasonic oscillator can be used as the ultrasonic oscillator 1, and for example, an ultrasonic cleaner AS52GTU (manufactured by AS ONE Corporation) can be used.

[0033] The output, oscillation frequency, and oscillation time of the ultrasonic oscillator 1 are not particularly limited as long as they are conditions that allow excessive dissolved nitrogen gas in the wastewater inside the collection vessel 20 to be degassed by ultrasonic treatment. For example, the output of the ultrasonic oscillator 1 is typically 50 to 1,000 W, preferably 100 to 500 W, and more preferably 150 to 300 W per liter of wastewater contained in the collection vessel 20. The oscillation frequency of the ultrasonic oscillator 1 is typically 20 to 200 kHz, preferably 25 to 100 kHz, and more preferably 30 to 75 kHz. The ultrasonic oscillation time is typically 1 to 150 minutes, preferably 5 to 120 minutes, and more preferably 10 to 100 minutes. The temperature of the water bath is typically set to the temperature of the wastewater when it is collected from the activated sludge tank, but is preferably 10 to 40°C, and more preferably 15 to 30°C.

[0034] The collection container 4 (collection means) is not particularly limited as long as it is a means capable of collecting the nitrogen gas generated inside the collection container 20, but for example, it is a syringe 4a with a piston 4b inside, and does not need to be equipped with a needle (Fig. 1). The syringe 4a displays a scale for measuring the volume of collected nitrogen gas, and the volume of gas that can be measured by the collection container 4 is usually 1 to 20 mL. When measuring the amount of nitrogen gas generated by irradiating the wastewater inside the collection container 20 with ultrasound, the top of the opening / closing mechanism 22 of the collection container 20 is connected to the tip of the syringe 4a (Fig. 2(B)).

[0035] 1 and 3 is a simple device equipped with a collection vessel 20 (collection means), an ultrasonic oscillator 1 (ultrasonic wave generating means), and a collection vessel 4 (collection means). By using such a simple device, the present invention can accurately measure the amount of dissolved nitrogen gas that is dissolved in excess of the saturation amount in wastewater containing activated sludge.

[0036] FIG. 4 is a flowchart showing the procedure of the nitrogen gas amount measurement process executed by the measurement device of FIG.

[0037] In the measurement process (measurement method) of FIG. 4 , first, wastewater is sampled from the activated sludge tank and collected in collection container 20 (S41: collection step). The deeper the water in the activated sludge tank, the higher the pressure of the wastewater. Furthermore, the amount of nitrogen gas dissolved in the wastewater is proportional to the pressure under certain conditions. Therefore, the deeper the water in the activated sludge tank, the higher the solubility of nitrogen in the wastewater. If wastewater below the water surface in the activated sludge tank is sampled, some of the dissolved nitrogen gas will bubble due to changes in water pressure when the sampled wastewater is brought back to the water surface, making it impossible to accurately measure the amount of dissolved nitrogen gas. Therefore, in this embodiment, the wastewater sampled from the activated sludge tank for measuring the amount of nitrogen gas is sampled from the water surface. Note that the gases dissolved in the wastewater sampled from the activated sludge tank also include gases such as carbon dioxide in addition to nitrogen. However, the amounts of these gases dissolved are so small compared to the amount of dissolved nitrogen that they are not considered in this embodiment.

[0038] The wastewater collected from the activated sludge tank in the collection step (S41) contains activated sludge, which is microorganisms or bacteria, and the MLSS concentration (activated sludge suspended solids concentration) in the collected wastewater is typically 1,000 to 30,000 mg / L, preferably 1,500 to 10,000 mg / L. The volume of wastewater collected in collection vessel 20 is typically 300 to 1,000 mL, but is not particularly limited as long as the volume of degassed nitrogen gas finally measured corresponds to the volume of collection vessel 4, for example, 1 to 20 mL. The wastewater collected from the activated sludge tank is poured into collection vessel 20, for example, through opening 21b of storage section 21 from which holding section 24 has been removed (FIG. 3).

[0039] Next, the holder 24, the connecting pipe 23, and the opening / closing mechanism 22 are connected to the opening 21b at the top of the storage part 21 (FIG. 3). At this time, since air and bubbles that were mixed in during the collection of the wastewater are present inside the collection container 20, the opening / closing mechanism 22 is opened, and the wastewater inside the collection container 21a is pushed from the outside to discharge the air and bubbles from the top of the opening / closing mechanism 22 (S42). After the air and bubbles present inside the collection container 20 have been completely discharged, the opening / closing mechanism 22 is closed to seal the collection container 20 (S42, FIG. 3).

[0040] Next, ultrasonic treatment is performed on the wastewater in the sealed collection container 20 (S43: ultrasonic wave generation step). First, the sealed collection container 20 is immersed in a water bath inside the ultrasonic oscillator 1 (FIG. 2(A)). The ultrasonic oscillator 1 supplies high-frequency power generated by the oscillator 2 to the transducer 3, which then generates ultrasonic waves (FIG. 2(A)). The output, oscillation frequency, and oscillation time of the ultrasonic oscillator 1 are appropriately selected so as to efficiently degas the dissolved nitrogen gas in excess in the wastewater inside the collection container 20 by ultrasonic treatment. For example, the output of the ultrasonic oscillator 1 is typically 50 to 1000 W, preferably 100 to 500 W, and more preferably 150 to 300 W per 1 L of wastewater contained in the collection container 20. The oscillation frequency of the ultrasonic oscillator 1 is typically 20 to 200 kHz, preferably 25 to 100 kHz, and more preferably 30 to 75 kHz. The ultrasonic oscillation time is usually 1 to 150 minutes, preferably 5 to 120 minutes, and more preferably 10 to 100 minutes. The temperature of the water bath is usually set to the temperature of the wastewater when it is collected from the activated sludge tank, and is preferably 10 to 40°C, and more preferably 15 to 30°C.

[0041] When ultrasonic treatment is performed, only the nitrogen gas that was dissolved in excess of the saturation amount in the wastewater inside collection container 20 is degassed, but the nitrogen gas that was dissolved in the wastewater at a saturated amount is not degassed. Whether or not the nitrogen gas that was dissolved in excess of the wastewater inside collection container 20 has been completely generated can be confirmed by measuring the total dissolved nitrogen gas in the wastewater inside collection container 20.

[0042] When the ultrasonic treatment is completed, bubbles of generated nitrogen gas are present in the wastewater inside collection container 20. Next, collection container 20 is connected to collection container 4 (S44) to measure the amount of nitrogen gas present inside collection container 20. Gas collection container 4 is a syringe (syringe) 4a equipped with a piston (push rod) 4b inside, and the volume of gas that can be measured by the syringe is 1 to 20 mL.

[0043] Specifically, the opening / closing mechanism 22 (closed) of the collection container 20 and the syringe 4a with the piston 4b inserted therein are immersed in a water bath within the ultrasonic oscillator 1, and the upper part of the opening / closing mechanism 22 (closed) and the interior of the syringe 4a are filled with water. Next, after confirming that no air bubbles are present above the opening / closing mechanism 22 (closed) or inside the syringe 4a, the tip of the syringe 4a is connected to the upper part of the opening / closing mechanism 22 in the water bath (S44, FIG. 2(B)). Thereafter, the opening / closing mechanism 22 is opened, and the piston 4b inside the syringe 4a is repeatedly pushed in and pulled out, thereby transferring the gas (air bubbles) inside the collection container 20 into the syringe 4a (S45, FIG. 2(B)). After confirming that all the gas (air bubbles) inside the collection container 20 have transferred to the syringe 4a, the opening / closing mechanism 22 is closed, and the volume of gas present inside the syringe 4a at this time is measured (S46). Furthermore, the weight of the syringe 4a and piston 4b with gas collected inside is measured using the weighing scale 5, and the weight of the degassed gas is measured by subtracting the weight of the syringe 4a and piston 4b measured when no gas is collected (S46). The degassed nitrogen concentration is calculated as the volume of nitrogen gas generated per 1 L of collected wastewater. The amount of nitrogen gas is measured as described above, and this measurement process is completed.

[0044] According to the measurement process shown in FIG. 4, wastewater is collected from the activated sludge tank and collected in collection container 20 (S41). Air and bubbles inside collection container 20 are then discharged from the top of opening / closing mechanism 22 (open), and collection container 20 is sealed (S42). Next, the sealed collection container 20 is immersed in a water bath inside ultrasonic oscillator 1 and ultrasonic treatment is performed (S43), thereby forming bubbles in collection container 20 from nitrogen gas dissolved in excess of the wastewater beyond the saturation level. Thereafter, collection container 20 and collection container 4 are connected (S44). After the nitrogen gas bubbles inside collection container 20 are transferred to storage container 4 (S45, FIG. 2(B)), the amount of nitrogen gas present inside storage container 4 is measured (S46, FIG. 2(C)). That is, by measuring the amount of dissolved nitrogen gas in wastewater using the measurement process shown in FIG. 2, the amount of nitrogen gas dissolved in excess of the wastewater can be accurately and simply measured, even when the wastewater contains activated sludge.

[0045] An activated sludge tank typically has an aeration device installed at its bottom, and air containing oxygen and nitrogen is aerated into the tank from its bottom. For example, if the activated sludge tank is 8 m or deeper, the deeper the tank, the greater the solubility of nitrogen in wastewater. Therefore, when wastewater is transferred to a final settling tank, which is shallower than the activated sludge tank, bubbles of insoluble nitrogen gas may form, causing the activated sludge to float. Since the floating of activated sludge in the final settling tank correlates with the amount of nitrogen gas dissolved in excess in the wastewater from the activated sludge tank, the present invention is particularly effective when measuring the amount of nitrogen gas dissolved in excess in wastewater in a deep activated sludge tank. [Example]

[0046] Next, an embodiment of the present invention will be described.

[0047] (Preliminary experiment 1: Degassing of nitrogen-saturated water and nitrogen-supersaturated water by ultrasonic treatment) Using the measuring devices of Figures 1 and 3, nitrogen-saturated water and nitrogen-supersaturated water were ultrasonically treated according to the measurement method of Figure 2, and the amount of nitrogen gas degassed from the nitrogen-saturated water and nitrogen-supersaturated water was measured. Nitrogen-saturated water was prepared by aerating fresh water with nitrogen gas at 25°C and atmospheric pressure for 30 minutes or more, and nitrogen-supersaturated water was prepared by aerating fresh water with nitrogen gas at 25°C and pressure for 30 minutes or more and sampling at atmospheric pressure. Here, the nitrogen-supersaturated water obtained by aeration under pressure of 0.05 MPa was designated "nitrogen-supersaturated water 1," and the nitrogen-supersaturated water obtained by aeration under pressure of 0.08 MPa was designated "nitrogen-supersaturated water 2."

[0048] First, three collection containers 20 (Figure 3) were prepared, and the holding portion 24 was removed from the opening 21b at the top of the storage portion 21. 600 mL of the nitrogen-saturated water, nitrogen-supersaturated water 1, and nitrogen-supersaturated water 2 prepared as described above were poured into each of the collection containers 20 through the opening 21b. The storage container 21a of the collection container 20 was a "Mighty Pack" (600 mL capacity) manufactured by Maruemu Co., Ltd. This "Mighty Pack" had a two-layer film structure (reflectance RI: 0.12) with a polyamide outer layer (thickness 18 μm) and a polyethylene inner layer (thickness 130 μm).

[0049] Next, the holding section 24, the connecting pipe 23, and the opening / closing mechanism 22 were connected to the opening 21b of each collection container 20 (Fig. 3). At this time, the wastewater inside the container 21 was pushed from the outside of the container 21, pushing out bubbles in the wastewater and air inside the collection container 20, and all gas present inside the collection container 20 was discharged to the outside through the opening / closing mechanism 22 (open state). The opening / closing mechanism 22 was then closed to seal the collection container 20. The sealed collection container 20 was immersed in a water bath inside the ultrasonic oscillator 1, and ultrasonic waves were irradiated from the transducer 3 of the ultrasonic oscillator 1 to the water inside the collection container 20 to perform ultrasonic treatment (Fig. 2(A)). The ultrasonic oscillator 1 used was an AS52GTU (manufactured by AS ONE Corporation), and the transducer was a bolt-tightened Langevin type transducer. The oscillation output of the ultrasonic oscillator 1 was 200 W, the water bath temperature was 25°C, the oscillation frequency was 35 kHz, and the oscillation time was set to 2, 5, 30, 60, and 90 minutes.

[0050] When each collection container 20 was subjected to ultrasonic treatment, no bubbles were generated from the nitrogen-saturated water (nitrogen gas was aerated under normal pressure), but bubbles were generated from the nitrogen-supersaturated water 1 and nitrogen-supersaturated water 2 (both of which were nitrogen gas aerated under pressure) (Fig. 2(A)). Next, the opening / closing mechanism 22 (closed) of the collection container 20 and the syringe 4a with the piston 4b inserted were immersed in a water bath inside the ultrasonic oscillator 1. After confirming that no bubbles were present inside, the tip of the syringe 4a was connected to the top of the opening / closing mechanism 22 (Fig. 2(B)). Thereafter, the opening / closing mechanism 22 was opened, and the piston 4b was repeatedly pushed into and pulled out of the syringe 4a, thereby transferring the bubbles inside the collection container 20 into the syringe 4a (Fig. 2(B)). After confirming that all of the bubbles inside the collection container 20 had transferred into the syringe 4a, the opening / closing mechanism 22 was closed, and the volume of gas present inside the syringe 4a was measured. The weight of the syringe 4a and piston 4b with gas collected inside was measured, and the weight of the syringe 4a and piston 4b without gas collected inside was subtracted to measure the weight of the degassed gas (FIG. 2(C)). The degassed nitrogen concentrations thus determined for nitrogen-saturated water, nitrogen-supersaturated water 1, and nitrogen-supersaturated water 2 are shown in Table 1 below. The degassed nitrogen concentration was calculated as the volume (mL / L) of nitrogen gas generated per 1 L of wastewater collected in the collection container 20.

[0051] [Table 1]

[0052] From the results in Table 1, in the case of nitrogen-saturated water in which the saturated amount of nitrogen gas was dissolved, ultrasonic treatment did not degas the nitrogen gas from the nitrogen-saturated water, and the degassed nitrogen concentration could not be measured. On the other hand, in the case of nitrogen-supersaturated water 1 and nitrogen-supersaturated water 2, in which excess nitrogen gas was dissolved beyond the saturation amount, ultrasonic treatment degassed the nitrogen gas from the nitrogen-supersaturated water, and the degassed nitrogen concentration could be measured. Furthermore, in the case of nitrogen-supersaturated water 1 and nitrogen-supersaturated water 2, the degassed nitrogen concentration tended to increase as the ultrasonic oscillation time increased. Furthermore, nitrogen-supersaturated water 2 (0.08 MPa), which was pressurized at a higher pressure, had a higher degassed nitrogen concentration than nitrogen-supersaturated water 1 (0.05 MPa). From this preliminary experiment 1, it was confirmed that ultrasonic treatment cannot degas nitrogen gas dissolved at the saturated amount, but it can degas nitrogen gas dissolved in excess beyond the saturation amount, and as a result, the amount of excess dissolved nitrogen gas can be measured.

[0053] (Preliminary experiment 2: Comparison of measurements using ultrasonic treatment and total dissolved nitrogen measurements) To confirm the accuracy of the measurement of degassed nitrogen concentration using ultrasonic processing (hereafter referred to as "ultrasonic measurement"), the results of the ultrasonic measurement were compared with the results of a known method for measuring total dissolved nitrogen concentration (hereafter referred to as "total dissolved nitrogen measurement"). The ultrasonic measurement was carried out in the same manner as in Preliminary Experiment 1, except that the oscillation time from Ultrasonic Oscillator 1 was set to 60 minutes. The total dissolved nitrogen measurement was carried out using the following method described in "Water Quality Survey for Beginners (III) Nitrogen Gas Measurement" by Shimizu Ikutaro (Salmon and Trout Resources Management Center Technical Information, Vol. 153, pp. 26-29 (1983 / 07)).

[0054] [Total Dissolved Nitrogen Measurement Method] (1) Concentrated hydrochloric acid and marble were added to the sample water collected in a water sampling bottle to generate carbon dioxide gas, which replaced the dissolved gas in the sample water with carbon dioxide gas and degassed the sample water. (2) Carbon dioxide and oxygen were removed from the gas in the water bottle by dissolving them in alkaline Rochelle solution and pyrogallol solution, respectively. (3) The volume of the remaining gas (essentially nitrogen gas only) was measured to obtain the total dissolved nitrogen concentration (ml / L) in the sample water. The above operations were carried out carefully so as not to let air get into the equipment.

[0055] The dissolved nitrogen concentration measured by the above "total dissolved nitrogen measurement" is the concentration of nitrogen gas (dissolved nitrogen gas) that is the sum of nitrogen gas dissolved in water in a saturated state and nitrogen gas dissolved in water in a supersaturated state. Therefore, the concentration of nitrogen gas dissolved in water in a supersaturated state can be calculated by subtracting the theoretical value of the nitrogen saturation concentration under the measurement conditions from the total dissolved nitrogen concentration.

[0056] First, total dissolved nitrogen measurements were performed on nitrogen-saturated water prepared by aerating fresh water with nitrogen gas under normal pressure. The differences between the measured dissolved nitrogen concentrations (aeration water temperature 20°C: 16.2 mL / L, aeration water temperature 30°C: 12.9 mL / L) and the theoretical values ​​for nitrogen saturation concentrations (water temperature 20°C: 15.5 mL / L, water temperature 30°C: 13.6 mL / L) were -0.7 and 0.7 mL / L (less than 4.5%), confirming that total dissolved nitrogen measurements can accurately measure the nitrogen gas concentration in nitrogen-saturated water in which the saturated amount of nitrogen is dissolved.

[0057] Next, fresh water was aerated with nitrogen gas at 25°C and various pressures (0.03, 0.05, 0.08, and 0.10 MPa) for 30 minutes or more, and then sampled at normal pressure to prepare nitrogen-supersaturated water. Total dissolved nitrogen and ultrasonic measurements were performed on the prepared nitrogen-supersaturated water. The concentration obtained by total dissolved nitrogen measurement was designated as dissolved nitrogen concentration a. The concentration obtained by ultrasonic measurement plus the theoretical nitrogen saturation concentration (14.5 mL / L) under the measurement conditions was designated as dissolved nitrogen concentration b. The difference (ab) between the two measurements is shown in Table 2 below, where the value obtained by subtracting the dissolved nitrogen concentration b obtained by ultrasonic measurement from the nitrogen saturation concentration a obtained by total dissolved nitrogen measurement is the error between the two measurements.

[0058] [Table 2]

[0059] The results in Table 2 show that the error (ab) between the dissolved nitrogen concentration a obtained by total dissolved nitrogen measurement and the dissolved nitrogen concentration b obtained by ultrasonic measurement was -0.2 to 2.2 mL / L (less than 8.4%), and the dissolved nitrogen concentrations determined by both measurement methods were in good agreement. This confirms that ultrasonic measurement can measure degassed nitrogen concentration with an accuracy of 91% or more compared to total dissolved nitrogen measurement. The results of this preliminary experiment 2 support the results of the above preliminary experiment 1, which showed that ultrasonic treatment can accurately measure only the amount of excess dissolved nitrogen gas.

[0060] (Example 1: Measurement of deaerated nitrogen concentration in wastewater containing activated sludge) Dissolved nitrogen concentrations were measured for wastewater undergoing treatment in an activated sludge tank (12 m deep) equipped with an aeration device, using total dissolved nitrogen and ultrasonic measurements. The relationship between dissolved nitrogen concentration and the flotation phenomenon of activated sludge was also investigated. Ultrasonic measurements were performed in the same manner as in Preliminary Experiment 1, except that the oscillation time from Ultrasonic Generator 1 was set to 60 minutes. The wastewater used for the measurements was wastewater (measured twice) from an activated sludge tank with intermediate aeration (swirl flow) that aerates from the middle of the tank (aeration device depth of 5 m), and wastewater (measured five times) from an activated sludge tank with bottom aeration that aerates from the entire bottom of the tank (aeration device depth of 11.5 m). In both cases, wastewater was collected from the water surface.

[0061] Ultrasonic measurement allowed for the measurement of degassed nitrogen concentration without any problems, even when activated sludge was present in the wastewater. The degassed nitrogen concentration measured here is the concentration of nitrogen gas dissolved in excess of the saturation level in the wastewater. Table 3 shows the results of ultrasonic measurements of the degassed nitrogen concentration and SV30 (activated sludge settling rate). SV30 (activated sludge settling rate) is an index of the settling ability of activated sludge and is the sludge volume (volume ratio) when activated sludge is allowed to stand in a measuring cylinder (40 cm deep) for 30 minutes. Table 3 also shows the calculated water depth at which all nitrogen at that concentration dissolves and is no longer in a supersaturated state (hereinafter referred to as the "water depth equivalent to complete dissolution"), assuming that all dissolved gas in the measured degassed nitrogen concentration is nitrogen gas.

[0062] [Table 3]

[0063] The results in Table 3 confirm that ultrasonic treatment can be used to measure the degassed nitrogen concentration of wastewater containing activated sludge, regardless of the aeration method. Furthermore, the concentration of nitrogen gas dissolved in excess of the saturation level in wastewater containing activated sludge (degassed nitrogen concentration) could not be measured using known total dissolved nitrogen measurement methods. Therefore, the present invention, which can measure degassed nitrogen concentrations that could not be measured using conventional methods, offers significant advantages. Furthermore, the degassed nitrogen concentration of wastewater sampled from a bottom aeration activated sludge tank was significantly higher than that of wastewater sampled from an intermediate aeration (swirl flow) activated sludge tank. Thus, the degree of supersaturation of nitrogen gas dissolved in wastewater containing activated sludge can be expressed as an index using the degassed nitrogen concentration obtained by ultrasonic measurement.

[0064] Furthermore, while SV30 could be measured for wastewater collected from an intermediate aeration (swirl-flow) activated sludge tank, SV30 could not be measured for wastewater collected from a bottom aeration activated sludge tank due to sludge floating. Comparing deaerated nitrogen concentration and SV30, sludge did not float and SV30 could be measured when the deaerated nitrogen concentration was 18 ml / L or less, but sludge floated when the deaerated nitrogen concentration was 20 ml / L or more, making SV30 measurement difficult. In other words, activated sludge tends to float easily in wastewater with a high deaerated nitrogen concentration, and the concentration of nitrogen gas dissolved in excess of the saturation level in the wastewater is correlated with activated sludge floating.

[0065] Therefore, when it is desired to suppress the floating of activated sludge in wastewater transferred from the activated sludge tank to the final settling tank, for example, the present invention can be used to measure the degassed nitrogen concentration in the wastewater in the activated sludge tank, and by comparing the measured degassed nitrogen concentration with the solubility of nitrogen gas in the final settling tank, it is possible to appropriately reduce and control the amount of air aeration from the aeration device.

[0066] Furthermore, in the case of wastewater collected from an intermediate aeration type (swirl flow type) activated sludge tank, the sludge did not float up to a depth equivalent to complete dissolution of 1.6 m, but in the case of wastewater collected from a bottom aeration type activated sludge tank, the sludge floated up when the depth equivalent to complete dissolution exceeded 3.3 m, so there is a correlation between the depth equivalent to complete dissolution and the floating of activated sludge.However, in the final settling tank, the depth of the water bottom where the sludge is settling determines whether the dissolved gas concentration is supersaturated, so the amount of air aeration from the aeration device can be controlled taking into account the depth equivalent to complete dissolution of the activated sludge tank and the depth of the water bottom where the sludge is settling in the final settling tank.

[0067] As described above, the measuring device and method of the present invention can accurately and easily measure the amount of nitrogen gas dissolved in excess of the saturation level in wastewater containing activated sludge, which cannot be measured by conventional total dissolved nitrogen measurement methods. Furthermore, the present invention makes it possible to grasp the tendency of activated sludge to float in wastewater transferred from the activated sludge tank to the final settling tank, and to control the floating of activated sludge in the final settling tank by appropriately adjusting the aeration rate from the aeration device in the activated sludge tank.

[0068] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. [Explanation of symbols]

[0069] 1 ultrasonic oscillator 4. Collection containers 10. Nitrogen gas volume measuring device 20 Collection container 22 Opening and closing mechanism

Claims

1. A measuring device for measuring the amount of nitrogen gas dissolved in excess in wastewater containing activated sludge, a collection means for collecting the wastewater; an ultrasonic wave generating means for generating ultrasonic waves to be transmitted to the collecting means; and collecting means for collecting gas generated in the wastewater captured by the capturing means.

2. 2. The measuring device according to claim 1, wherein the collecting means comprises a container formed of a resin material, and the resin material has an ultrasonic reflectivity RI of 0.2 or less at the interface between the resin material and water.

3. 2. The measuring device according to claim 1, wherein the collecting means comprises an opening and closing mechanism.

4. 2. The measuring device according to claim 1, wherein the ultrasonic wave generated by said ultrasonic wave generating means has an oscillation frequency of 20 to 200 kHz.

5. A method for measuring the amount of nitrogen gas dissolved in excess in wastewater containing activated sludge using a measuring device having a collection means for collecting the wastewater, comprising: a collecting step of collecting the wastewater; an ultrasonic wave generating step of generating ultrasonic waves to be transmitted to the collecting means; a collecting step of collecting gas generated in the wastewater collected in the collecting means.

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