JP2019063734A - Oxygen supply system, water treatment system and oxygen supply method - Google Patents

Abstract

To provide an oxygen supply system, a water treatment system, and an oxygen supply method capable of increasing oxygen dissolution efficiency to power.SOLUTION: A system includes: an aeration tank for holding aeration target water; an air diffuser that releases oxygen-containing bubbles to the aerated target water; and a swirling flow generating device provided below the air diffuser and configured to swirl water mass with dissolved oxygen in the aeration tank without lowering air bubbles released by the air diffuser. The air diffuser may be installed near a free interface to promote oxygen dissolution at the free interface of the aeration target water.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an oxygen supply system, a water treatment system and an oxygen supply method.

  At present, sewage treatment plants in Japan mainly adopt activated sludge method, which is a typical treatment method of organic matter decomposition by aerobic microorganisms. In the activated sludge method, aeration operation is indispensable for supplying oxygen to aerobic microorganisms and stirring in the tank. In the past, the consumption of electricity used for this aeration amounted to about 40 to 50% of the total electricity consumed at sewage treatment plants. In order to reduce the energy consumption for aeration, it is necessary to increase the efficiency of oxygen dissolution in water to reduce the amount of air flow for aeration.

  There are the following two paths for dissolving oxygen in the aeration target water in the aeration tank. The first path is a path in which oxygen is dissolved in the aeration target water from the air bubbles generated by the aeration device. The second route is a route in which oxygen dissolves from the free interface of the aeration target water.

  In the prior art, for example, by a diffuser for coarse bubble generation disposed at the bottom of the aeration tank, a predetermined angle is made to the water surface in a circulating water basin generated over the entire inside of the aeration tank. The screw-type aeration device ejects fine air bubbles for aeration to the downward circulating water basin near the water surface, and the water flow generated by the screw of the screw-type aeration device is generated by the aeration device for rough bubble generation There has been proposed an aeration method in which fine bubbles are put on a downward circulating water flow and retained in the circulating water flow so as to join the water flow (see, for example, Patent Document 1).

  In recent years, the introduction of a diffuser having increased oxygen dissolution efficiency has progressed by miniaturizing the bubbles to enlarge the gas-liquid contact area (the specific surface area of the bubbles). Thus, although studies to increase the oxygen dissolution efficiency by air bubbles in aerated water are widely performed, there are few cases in which the oxygen dissolution efficiency from the free interface is examined. However, in a system having a wide free interface, such as an aeration tank, oxygen dissolution from the free interface is known to account for a high proportion of total oxygen dissolution (see, for example, Non-Patent Documents 1 and 2).

Patent No. 3336326 Patent No. 5110876 gazette Japanese Patent Application Laid-Open No. 6-91298

DeMoyer, C. D., E. L. Schierholz, J. S. Gulliver, & S. C. Wilhelms; "Impact of Bubble and Free Surface Oxygen Transfer on Diffused Aeration Systems." Water Res., 37 (8), 1890-1904 (2003). K. Shibata, K. terasaka, S. Fujioka, & K. "Oxygen Transfer from a Free Surface and Dispersed Bubbles in an Aeration Tank." Journal of Chemical Engineering of Japan., 49 (5), 391-398 ( 2016). Nokuninsuke Tokunaga, et al., “Study on the examination of the reduction effect of aeration tank by introducing liquid film type oxygen supply method”, Proceedings of the China National Conference of the Civil Society, 2010, Vol. 62, VII-15

  In the prior art, for example, when aeration bubbles are jetted into the circulating water flow downward and put the bubbles on the downward circulating water flow, it is necessary to flow the bubbles downward against the buoyancy of the bubbles to generate the circulating water flow. In order to require a large amount of energy. On the other hand, by actively utilizing oxygen dissolution from the free interface, it is possible to save energy and perform aeration with a high oxygen dissolution rate. This invention is made in view of the above, Comprising: It aims at providing the oxygen supply system, water treatment system, and oxygen supply method which can make high the oxygen dissolution efficiency with respect to motive power.

  In order to solve the problems described above and achieve the object, an oxygen supply system according to an aspect of the present invention includes an aeration tank for holding a water to be aerated, and an aeration tank for releasing air bubbles containing oxygen in the aeration target water. And a swirl flow generating device provided below the air diffuser and causing the water mass in which oxygen is dissolved to swirl in the air tank without lowering the air bubbles released by the air diffuser. It is characterized by

  In the oxygen supply system according to one aspect of the present invention, the aeration device may release bubbles including oxygen upward to promote aeration at the free interface of the aeration target water.

  Further, in the oxygen supply system according to one aspect of the present invention, the swirl flow generation device releases a coarse bubble having an oxygen dissolution efficiency lower than that of the bubble released by the aeration device, whereby a water mass in which oxygen is dissolved. May be pivoted within the aeration tank.

  In the oxygen supply system according to one aspect of the present invention, the swirl flow generation device may swirl a water mass in which oxygen is dissolved in the aeration tank by rotating a stirring member.

  Further, in the oxygen supply system according to one aspect of the present invention, the swirl flow generation device is disposed such that a distance from the water surface of the aeration target water to the water depth of the aeration tank is two thirds or less. It may be done.

  In the oxygen supply system according to one aspect of the present invention, the aeration device may be disposed such that the distance from the water surface of the aeration target water is less than or equal to half.

  A water treatment system according to one aspect of the present invention includes the above-described oxygen supply system, and the aeration target water is treated water containing an aerobic organism that decomposes an organic matter.

  In the oxygen supply method according to one aspect of the present invention, the aeration target water held in the aeration tank is caused to release bubbles containing oxygen from the diffuser, and the bubbles released from the diffuser are lowered. And rotating the water mass in which the oxygen is dissolved.

  According to the present invention, the oxygen dissolution efficiency with respect to power can be increased.

It is a figure showing an outline of an oxygen supply system concerning one embodiment. It is a figure showing an outline of a modification of an oxygen supply system. It is a figure which shows the outline | summary of the oxygen supply system for experiment provided with the function which the oxygen supply system concerning one Embodiment has. (A) is a figure which shows the cross section of an aeration tank, a diffuser, and a rotational flow production | generation apparatus. (B) is the top view which looked at an aeration tank, a diffuser, and the rotational flow production | generation apparatus from upper direction. (A) is sectional drawing of the aeration tank which shows arrangement | positioning of DO meter. (B) is a top view of the aeration tank which shows arrangement | positioning of DO meter. To the case of aeration from the air diffuser alone is a graph showing the K _{L a} with respect to aeration energy in the case of aeration from the air diffuser and a swirling flow generator. (A) is a figure which shows a whole surface aeration system. (B) is a figure which shows a rotational flow aeration system.

First, techniques widely adopted in sewage treatment plants where the present invention can be used will be described.
Activated sludge method widely adopted in sewage treatment plants is a treatment method utilizing organic matter decomposition by aerobic microorganisms, and it is necessary to supply oxygen to microorganisms. In order to supply oxygen to microorganisms, a method of aerating air with a diffuser is mainly used. The efficiency of dissolving oxygen in water is called oxygen transfer efficiency (OTE). The higher the OTE, the more the amount of air blown to generate air bubbles can be reduced, which results in energy saving. OTE is expressed by the following equation (1).

In the above equation (1), only K _L a is a variable and is one of the indices of the oxygen supply capacity. That is, in the same aeration tank, the air blowing amount to the aeration device that generates air bubbles, Cs (dissolved oxygen concentration in equilibrium state) influenced by water temperature, and ρ (air density) influenced by air blowing temperature are identical. In this case, the larger the K _L a, the higher the OTE and the energy saving.

Also, as described above, in the path for dissolving oxygen in the aeration target water in the aeration tank, the path in which oxygen is dissolved in the aeration target water from the bubbles generated by the aeration device, and the oxygen from the free interface of the aeration target water There are two ways in which With respect to oxygen dissolved from these two paths, the total material (oxygen) transfer capacity coefficient K _L a of the entire aeration tank is represented by the following equation (2).

Further, in a system having a wide free interface such as an aeration tank, oxygen dissolution (oxygen transfer) from the free interface is not negligible. In the non-patent document 1 described above, the experiment was performed using a cylindrical aeration tank with a diameter of 7.6 m and a depth of 9.25 m, and the result of calculating the overall mass transfer capacity coefficient (K _L a) _s at the free interface is shown It is done. Here, it is reported that the value of (K _L a) _s was 59 to 85% with respect to the overall mass transfer capacity coefficient (K _L a) _b between water and bubbles.

Further, in Non-Patent Document 2 described above, mass transfer at the free interface is considered to be affected by the flow state (turbulence) near the free interface, and the overall mass transfer capacity coefficient (K _L ) at the free interface a) _s is corrected as expressed in the following equation (3).

u _LS W / ν _L corresponds to the Reynolds number and represents the flow state near the free interface. Therefore, if an increase is _{U LS} be more disturbed near the free interface, overall correction value for the mass transfer capacity coefficient _{(K L a) s,} the value of the _Mod increases.

In addition, in Non-Patent Document 2, in an aeration tank with a width of 5 m, a depth of 5 m, and a water depth of 5 m, the values of (K _L a) _s and _Mod are 40 to 70 of the overall mass transfer capacity coefficient K _L a of the entire aeration tank. It has been reported that it was%. Thus, in an aeration tank or the like having a wide free interface, oxygen transfer at the free interface accounts for a large proportion, and if the vicinity of the free interface is more disturbed, oxygen transfer at the free interface becomes larger.

  In the aeration tank, when water is filled and allowed to stand, oxygen dissolution proceeds only in the vicinity of the interface where water and air are in contact. And the concentration of oxygen dissolved in water is high near the water surface, and decreases as it gets deeper from the water surface. Therefore, in order to distribute the water in which oxygen is dissolved into the aeration tank, it is necessary to stir the water in the aeration tank. In order to agitate the water in the aeration tank, for example, a water flow produced as a result of the rise of the bubbles generated by the aeration device, or a water flow produced by mechanical stirring is used.

  Here, the aeration system according to the comparative example will be described with reference to FIG.

  FIG. 7 is a diagram showing an example of the aeration system according to the comparative example. FIG. 7A is a diagram showing the entire aeration system. FIG.7 (b) is a figure which shows a turning flow aeration system.

  In the full aeration system shown in FIG. 7A, water (water to be aerated) 2 is put in the aeration tank 1, and a plurality of diffusers 3 are provided over substantially the entire area near the bottom of the aeration tank 1. It is arranged at equal intervals. Each of the aeration devices 3 supplies oxygen to the water 2 by releasing air bubbles and bringing the air 2 into contact with the water 2 in the aeration tank 1 when compressed air is fed. In the full aeration system, the dispersiveness of air bubbles is improved by a plurality of aeration devices 3 disposed over substantially the entire area near the bottom of the aeration tank 1.

  Further, by arranging the aeration device 3 near the tank bottom surface of the aeration tank 1, the residence time of the aeration of the aeration device 3 in the water 2 of the aeration is lengthened, and the contact time of gas and liquid is prolonged. The oxygen dissolution efficiency is increased. However, since the aeration device 3 is disposed at a deep position in the water depth, a large power is required to feed compressed air to the aeration device 3.

  In the swirl flow aeration system shown in FIG. 7 (b), water 2 is put in the aeration tank 1, and a plurality of diffusers 3 are disposed on one wall side near the tank bottom of the aeration tank 1. When compressed air is fed into each of the plurality of air diffusers 3, the plurality of air diffusers 3 release air bubbles to bring the water 2 in the aeration tank 1 into contact with the air bubbles and generate a water flow that becomes a swirling flow as the air bubbles rise. The swirling flow generated by the plurality of air diffusers 3 stirs the water 2 in the aeration tank 1.

  In addition, as an aeration system for supplying oxygen to water, there is also a surface aeration system in which a large amount of water is scattered in the air and scattered on the water surface by rotating a stirring blade installed on the water surface of the aeration tank. In this surface aeration system, the stirring blade stirs the water in the aeration tank while supplying oxygen to the water by causing oxygen movement due to intense turbulence of the water surface and oxygen movement to the water droplets scattered in the air.

  In addition, the liquid film of water is actively formed by air bubbles, and the contact area of water and oxygen is increased by simultaneously bringing the inside and the outside of the liquid film of water into contact with air simultaneously, thereby improving the oxygen dissolution efficiency. An oxygen supply system is also known (see, for example, Non-Patent Document 3 and Patent Document 2). However, conventionally, it has been difficult to increase the oxygen dissolution efficiency with respect to power.

  Next, one embodiment of an oxygen supply system, a water treatment system, and an oxygen supply method according to the present invention will be described in detail using the drawings.

  FIG. 1 is a schematic view of an oxygen supply system 100 according to an embodiment. The oxygen supply system 100 holds aeration target water 20 such as water targeted for aeration or water to be treated in the aeration tank 10, and the aeration device 30 is disposed at a shallow position near the water surface of the aeration target water 20. ing. In addition, the swirl flow generation device 40 is disposed at a position at which the distance from the water surface of the aeration target water 20 is, for example, about one half of the water depth of the aeration tank 10 on one wall side in the aeration tank 10. It is done. The swirling flow generating device 40 may be arranged such that the distance from the water surface of the aeration target water 20 to the water depth of the aeration tank 10 is two thirds or less. Thus, the swirling flow generating device 40 is provided below the aeration device 30.

  More specifically, the aeration device 30 is disposed such that the distance from the water surface of the aeration target water 20 is 1/2 or less of the water depth of the aeration tank 10, and the compressed air supplied from the outside is supplied To release a number of oxygen containing bubbles 300, for example, upward. For example, the aeration device 30 is disposed such that the distance from the water surface of the aeration target water 20 is about 0.1 to 0.2 m. A plurality of the aeration devices 30 may be arranged, for example, in the vicinity of the water surface of the aeration target water 20 so that a large number of air bubbles 300 are released to a wide range of the water surface of the aeration target water 20.

  The air bubbles 300 move oxygen to the aeration target water 20 while rising in the aeration target water 20 and cause a violent disturbance on the water surface of the aeration target water 20 to promote oxygen transfer from the atmosphere to the aeration target water 20. For example, the air bubble 300 forms a liquid film on the water surface of the aeration target water 20 and causes many droplets. In addition, the air bubbles 300 may be micro air bubbles so that the gas-liquid contact area (specific surface area) becomes large. For example, the bubble 300 may have a diameter of 2 to 3 mm or less immediately after foaming from the aeration device 30.

  As described above, the aeration device 30 is disposed so as to disturb the free interface of the aeration target water 20 or cause splashing / dropping of water droplets at the free interface to promote aeration. Further, the air diffuser 30 may have a configuration in which, for example, a plurality of holes are simply provided on the upper surface to release oxygen-containing bubbles upward, or the bubbles may be lowered (see Patent Document 1), or It does not have to be a configuration for horizontally releasing (see Patent Document 3).

  Furthermore, since the aeration device 30 is disposed at a shallow position near the water surface of the aeration target water 20, compression supplied from the outside is greater than when the water depth near the tank bottom is disposed at a deep position. Air bubbles 300 can be released even if the pressure of air is low. That is, the diffuser 30 can reduce the power of the external blower (or air compressor) required to discharge the air bubbles 300.

  Moreover, the aeration device 30 may clog the aeration depending on the water quality condition. In the case where the oxygen supply system 100 is provided with the air diffuser 30 near the free interface, the oxygen supply system 100 can be cleaned without lifting up the air diffuser 30 in order to eliminate clogging of the air diffuser 30.

  The swirl flow generation device 40 discharges, for example, a coarse air bubble 400 having a lower oxygen dissolution efficiency than the air bubble 300 released by the air diffusion device 30. Then, the swirling flow generation device 40 swirls the water mass of the aeration target water 20 in which the oxygen is dissolved in the aeration tank 10 without lowering the bubbles 300 released by the aeration device 30.

  For example, as shown in FIG. 1, the swirling flow generating device 40 generates a water flow by raising coarse bubbles 400 on one wall side in the aeration tank 10, and the other wall side on the opposite side in the aeration tank 10. To generate a descending water flow to generate a stirring flow A in the aeration tank 10. Here, the swirling flow generation device 40 supplies the water mass of the aeration target water 20 before the oxygen supplied from the aeration device 30 dissolves toward the aeration device 30, and the aeration target in which the oxygen is dissolved by the air bubble 300. A distance from the aeration device 30 is set to move a water mass of water 20 to the lower side of the aeration tank 10.

  As described above, since the oxygen supply system 100 does not need to generate a stirring flow by the swirl flow generation device 40 so as to cause the air bubbles 300 released by the air diffuser 30 to move down against the buoyancy, the swirl flow generation device 40 Energy required for the operation of the Moreover, since the oxygen supply system 100 does not require a complicated structure or many members, the workability is improved as compared with the conventional case (see, for example, Non-Patent Document 3).

  In addition, the oxygen supply system 100 is used as a water treatment system installed in a sewage treatment plant etc., when the aeration target water 20 is the to-be-processed water containing the aerobic organism which decomposes | disassembles organic substance. When the aeration target water 20 is treated water containing aerobic organisms, the swirl flow generation device 40 may release the coarse bubbles 400 to such an extent that the activated sludge in the aeration tank 10 does not settle on the tank bottom.

  In addition, the oxygen supply system 100 is used as a system for supplying oxygen to underwater organisms when the aeration target water 20 is, for example, fresh water and underwater organisms such as fish are released in the aeration target water 20.

  FIG. 2 is a diagram showing an outline of a modified example (oxygen supply system 100 a) of the oxygen supply system 100. As shown in FIG. 2, the oxygen supply system 100 a holds the aeration target water 20 such as the water to be aerated or the water to be treated in the aeration tank 10, and is at a shallow position near the water surface of the aeration target water 20. A diffuser 30 is arranged. In addition, a swirl flow generation device 42 is provided at, for example, the center of the aeration tank 10. Hereinafter, substantially the same components as those of the oxygen supply system 100 shown in FIG. 1 are denoted by the same reference numerals.

  The swirl flow generation device 42 includes, for example, a drive unit 420, an agitation member 422, and a support unit 424. The driving unit 420 is supported by the support unit 424 above the center of the water surface of the aeration target water 20, for example, and agitates the aeration target water 20 by rotating the stirring member 422. For example, the stirring member 422 is rotated by the drive unit 420 to generate a stirring flow B toward the wall surface side from the vicinity of the center in the aeration tank 10 through the bottom surface side. The position at which the stirring member 422 is provided may be another position below the air diffuser 30.

  As described above, according to the oxygen supply system 100 (or the oxygen supply system 100a) according to one embodiment, the oxygen dissolution efficiency with respect to power can be increased. That is, with the same oxygen dissolution efficiency, the oxygen supply system 100 can be realized with power smaller than that of the comparative example shown in FIG. 7, resulting in energy saving.

  Next, an experimental example showing the superiority of the oxygen dissolution efficiency in the oxygen supply system 100 will be described.

  FIG. 3 is a diagram showing an outline of an experimental oxygen supply system 100 b having the functions of the oxygen supply system 100.

  As shown in FIG. 3, the oxygen supply system 100b holds, for example, aeration target water 20b such as water to be aerated in the aeration tank 10b or water to be treated. A plurality of diffusers 30b are disposed at shallow depths near the water surface of the aeration target water 20b. For example, in the oxygen supply system 100b, four air diffusers 30b are arranged side by side (see FIG. 4).

  Further, on one wall side in the aeration tank 10b, a swirling flow generating device 40b is disposed in which the distance from the water surface of the aeration target water 20b is variable. The plurality of air diffusers 30b and the swirling flow generator 40b are connected to a pipe 500 so that, for example, compressed air supplied by the air compressor 50 is supplied.

  The air compressor 50 supplies compressed air containing oxygen through a pipe 500. Further, a nitrogen gas supply device 510 is connected to the pipe 500 via the switching valve 512. The switching valve 512 switches the connection destination for the pipe 500 between the air compressor 50 and the nitrogen gas supply device 510. The nitrogen gas supply device 510 supplies nitrogen through the pipe 500 in response to the switching operation of the switching valve 512. The control valve 51 is provided in the vicinity of the air compressor 50 of the pipe 500, and adjusts the air flow of compressed air (or nitrogen gas supplied by the nitrogen gas supply device 510) supplied by the air compressor 50. The needle valve 52 adjusts the flow rate (air flow rate) of the compressed air supplied from the air compressor 50 to the swirl flow generation device 40 b. The four needle valves 53 respectively adjust the flow rate of the compressed air supplied to the air diffuser 30b.

In the vicinity of the control valve 51, the needle valve 52 and the needle valve 53, flow indicators 54 for measuring the blowing amount (m ³ / min) of the compressed air are provided. In the vicinity of the needle valve 52 and the needle valve 53, pressure gauges 55 for measuring the pressure (kPa) of the compressed air are provided. Then, the air diffuser 30b discharges the predetermined air bubble 300, and the swirl flow generation device 40b discharges the predetermined coarse air bubble 400.

  In the aeration tank 10b, a plurality of DO (Dissolved Oxygen) meters 60 (see FIG. 5) for measuring the dissolved oxygen concentration are provided.

  FIG. 4 is a view showing an arrangement example of the aeration tank 10b, the aeration device 30b, and the swirl flow generation device 40b. Fig.4 (a) is a figure which shows the cross section of the aeration tank 10b, the aeration device 30b, and the rotational flow production | generation apparatus 40b. FIG.4 (b) is the top view which looked at the aeration tank 10b, the aeration device 30b, and the rotational flow production | generation apparatus 40b from upper direction.

  The aeration tank 10 b is, for example, a water tank having a width of 1400 mm, a depth of 1400 mm, and a water depth of 1400 mm. The diffuser 30b is, for example, a diffuser panel having a membrane size of 600 mm × 150 mm for discharging the air bubble 300. The four air diffusers 30b are arranged in two rows and columns so that the installation area is 15% of the area of the water surface of the aeration target water 20b.

  Specifically, in the two aeration devices 30b, the centers of the longitudinally aligned rows are separated 350 mm from the wall of the aeration tank 10b. Further, the diffusers 30b are arranged so that the distance in the longitudinal direction is 100 mm, and the end is separated 50 mm from the wall of the aeration tank 10b. Furthermore, in the aeration device 30b, the distance hd from the water surface of the aeration target water 20b is variable. For example, in the aeration device 30b, the distance hd from the water surface of the aeration target water 20b can be set to 200 mm, 400 mm, 600 mm, and 1300 mm.

  The swirl flow generating device 40b is, for example, a polyvinyl chloride pipe having a diameter of 40 mm and a length of 600 mm, and is a perforated pipe provided with 20 holes having a hole diameter of 4 mm. The swirling flow generating device 40b is separated by 100 mm from the wall of the aeration tank 10b, and the distance hp from the water surface of the aeration target water 20b is made variable. For example, in the swirling flow generating device 40b, the distances hp from the water surface of the aeration target water 20b can be set to 300 mm, 800 mm, and 1300 mm.

  FIG. 5 is a view showing the positions of a plurality of DO meters 60 provided in the aeration tank 10b. FIG. 5A is a cross-sectional view of the aeration tank 10 b showing the arrangement of the DO meter 60. FIG. 5B is a plan view of the aeration tank 10 b showing the placement of the DO meter 60. For example, four DO totals 60 are arranged in the aeration tank 10 b so as to measure the dissolved oxygen concentration at the positions of 300 mm, 600 mm, 900 mm and 1200 mm in water depth. Further, as shown in FIG. 5B, each DO meter 60 is separated 350 mm from one wall in the aeration tank 10 b and 250 mm from the other wall orthogonal to it.

  Next, a method of calculating the necessary aeration energy using the oxygen supply system 100b and evaluating the energy saving effect on the prior art by comparison will be described. Here, the worker performs the following operation using the oxygen supply system 100b.

  First, the worker supplies nitrogen gas from the nitrogen gas supply device 510 into the aeration tank 10 b to reduce the dissolved oxygen concentration to about 0 mg / L.

  Thereafter, compressed air of a predetermined air volume is supplied from the air compressor 50 to start aeration, and temporal change of dissolved oxygen is recorded. The measurement is ended when the dissolved oxygen concentration reaches approximately equilibrium.

Then, K _L a is calculated using the measurement result and the following equation (4).

Next, the aeration energy P is calculated using the following equations (5) and (6). The following equation (5) represents the aeration energy _{W i} of each air diffuser 30b (aeration panel) and the swirling flow generator 40b (perforated tube). The following equation (6) represents the overall aeration energy P of the oxygen supply system 100b.

The operator sequentially changes the distance h _d of the air diffuser 30 b and the distance h _p of the swirl flow generation device 40 b to perform the above-described operation.

FIG. 6 shows aeration energy when aeration is performed only from the aeration device 30b (aeration panel) using the above-described oxygen supply system 100b, and when aeration is performed from the aeration device 30b and the swirl flow generation device 40b (porous pipe). Is a graph showing the overall mass transfer capacity coefficient K _L a with respect to. In FIG. 6, white circles indicate the overall mass transfer capacity coefficient K _L a when aeration energy is changed by aeration from only the aeration device 30 b. In addition, black circles indicate the overall mass transfer capacity coefficient K _L a when aeration energy is changed by aeration from the aeration device 30 b and the swirl flow generation device 40 b.

The aeration energy and K _L a are proportional to each other as indicated by the linear approximation in both cases of aeration from the aeration device 30 b and aeration from the aeration device 30 b and the swirl flow generation device 40 b. is there. Further, the air blowing amount and the installation water depth for the air diffuser 30b and the swirling flow generator 40b have little influence on this proportional relationship.

However, when aeration is performed from the aeration device 30b and the swirling flow generation device 40b, the slope of the proportional relationship is larger than when aeration is performed only from the aeration device 30b. That is, when aeration is performed from the aeration device 30b and the swirl flow generation device 40b, a higher K _L a can be obtained with the same aeration energy as compared to a case where aeration is performed only from the aeration device 30b. It has become.

10, 10b: Aeration tank, 20, 20b: Aeration target water 30, 30, b: Aeration device, 40, 40b: Swirl flow generation device, 42: Swirl flow generation device, 50 ... Air compressor, 52, 53 ... Needle valve, 54 ... Flow indicator, 55 ... Pressure gauge, 60 ... DO meter, 100, 100a, 100b ... Oxygen supply system, 300 ... Bubbles, 400 ... Coarse bubbles, 420 ... Drive parts, 422 ... Stirring members, 500 ... Piping, 510 ... Nitrogen gas supply device, 512 ... Switching valve

Claims (8)

An aeration tank for holding aeration target water,
A diffuser for releasing bubbles containing oxygen into the aeration target water;
And a swirling flow generating device provided below the aeration device and causing a water mass in which oxygen is dissolved to be swirled in the aeration tank without lowering the air bubbles released by the aeration device. Oxygen supply system. In the oxygen supply system according to claim 1,
The diffuser is
An oxygen supply system characterized in that bubbles containing oxygen are discharged upward to promote aeration at the free interface of the aeration target water. In the oxygen supply system according to claim 1 or 2,
The swirling flow generating device is
An oxygen supply system characterized in that a water mass in which oxygen is dissolved is swirled in the aeration tank by releasing a coarse bubble having a lower oxygen dissolution efficiency than a bubble released by the aeration device. In the oxygen supply system according to claim 1 or 2,
The swirling flow generating device is
An oxygen supply system characterized in that a water mass in which oxygen is dissolved is swirled in the aeration tank by rotating a stirring member. The oxygen supply system according to any one of claims 1 to 4.
The swirling flow generating device is
The oxygen supply system is characterized in that the distance from the water surface of the aeration target water is equal to or less than two thirds of the water depth of the aeration tank. The oxygen supply system according to any one of claims 1 to 5,
The diffuser is
The oxygen supply system is characterized in that the distance from the water surface of the aeration target water to the water depth of the aeration tank is 1/2 or less. An oxygen supply system according to any one of claims 1 to 6, comprising:
The aeration target water is
A water treatment system characterized by being treated water containing aerobic organisms that decompose organic matter. Releasing bubbles containing oxygen in the aeration target water held in the aeration tank from the diffuser;
And D. swirling a water mass in which oxygen is dissolved without lowering the air bubbles released from the air diffuser.