JP3552230B2 - Oxidation ditch device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an oxidation ditch device for supplying oxygen to activated sludge for treating wastewater and the like.
[0002]
[Prior art]
The oxidation ditch device usually generates a circulating flow of a mixture of activated sludge and sewage in a tank body forming a circulation path at a horizontal level, and supplies oxygen to the mixture to purify sewage. Are doing.
[0003]
In order to generate a circulation path, a propeller device is provided in the tank main body, and a circulating flow is generated by rotating the propeller device, and the circulating flow, that is, the mixture is stirred. An air diffuser for generating air bubbles for supplying oxygen is disposed at the downstream side of the propeller device. The air bubbles are mixed in the downstream side of the propeller, and the wastewater is purified by the oxygen contained in the air bubbles. Is achieved.
[0004]
[Problems to be solved by the invention]
As for the power of the blower for the propeller device for stirring the mixture and the air blower for supplying air to the mixture as air bubbles, the latter blower is larger, and this is reduced from the viewpoint of energy saving. It is desired.
[0005]
In order to increase the oxygen supply efficiency, it is necessary to reduce the diameter of the bubbles and to increase the residence time of the bubbles in the mixture. One of the former measures is to reduce the pore diameter of the air diffuser for generating bubbles, but the clogging becomes easier to progress. As one of the latter measures, the water depth of the circulating flow of the mixture may be increased, but the effect is offset because the discharge pressure of the blower must be increased against the increase of the water pressure.
[0006]
As another measure, when a horizontal flow rate is applied to the bubble generation site of the air diffuser, the bubbles are sheared by the horizontal flow rate, the diameter of the bubbles is reduced, and the contact area of the bubbles with the sewage as a whole is increased. In this case, an air diffuser is installed at a position immediately downstream of the propeller device in the oxidation ditch.
[0007]
The propeller device is usually installed near the bottom of the tank body in order to prevent the accumulation of sludge at the tank bottom, so that the flow velocity distribution in the vertical (height) direction is high on the bottom side and low on the surface side. Therefore, the flow rate of the circulating flow is high on the bottom side where bubbles are generated, so that the generated bubbles are small and the oxygen dissolving efficiency is high.
[0008]
However, an air diffuser arranged downstream of the propeller device (for example, an air diffuser arranged on the opposite side of the propeller device) has a small and flat flow velocity distribution in the height direction, so that generated bubbles are relatively small. Large, oxygen dissolution efficiency is not improved.
[0009]
In view of such circumstances, the present invention, even in the case of an air diffuser arranged downstream of the propeller device that is not immediately adjacent to the propeller device (an air diffuser arranged on the opposite side of the propeller device), is not limited to the tank body just before the air diffuser device. It is an object of the present invention to provide an oxidation ditch capable of improving the oxygen dissolving efficiency by increasing the flow rate of a circulation flow on the bottom side.
[0010]
[Means for Solving the Problems]
The oxidation ditch device according to the present invention includes a tank body that forms a circulation path at a horizontal level, a circulating flow generator that generates a circulating flow along the circulation path, and a circulating flow that is disposed at the bottom of the tank body. A diffuser for generating rising bubbles.
[0011]
According to the present invention, in such an apparatus, a flow reducing device that converges the flow of the circulating flow on the bottom side of the tank main body in the upstream position of the air diffuser is disposed in the tank main body. The above-mentioned flow reducing device is formed as a current changing plate arranged at an angle so as to converge the circulating flow with the bottom of the tank body toward the downstream side.
[0012]
Therefore, in the device of the present invention, the flow on the bottom side of the tank body is converged by the flow reducing device, so that the flow velocity is increased. In such an accelerated flow, a large horizontal velocity component is also given when bubbles generated from the air diffuser rise, so that the bubbles are sheared and become finer, and the residence time in the flow becomes longer.
[0015]
The current change plates may be arranged at a plurality of positions in at least one of the direction of the flow of the circulating flow, the height direction and the width direction of the circulation path. It is preferable that the inclination angle can be changed.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an oxidation ditch device as an embodiment of the present invention will be described with reference to the accompanying drawings.
[0017]
FIG. 1 is a schematic plan view of the apparatus according to the present embodiment, and FIG. 2 is a view showing a flow velocity distribution in the height direction in the vicinity of the flow reducing device and the air diffusing device in FIG.
[0018]
In FIG. 1, a tank body 1 has an elliptical planar outer shape, and a partition wall 2 extending in a longitudinal direction is provided at a central portion, and a circulation path is formed around the partition wall 2. In addition, semicircular guide walls 3 are provided near both ends of the partition wall 2 so as to smoothly turn the flow in the circulation path.
[0019]
A propeller device 4 as a circulating flow generator is disposed at an appropriate position of the circulation path, in the illustrated example, at a position immediately upstream of the guide wall 3, and at a position downstream of the guide wall 3 at the bottom of the tank body. Is provided with an air diffuser 5. As shown in FIG. 2, the air diffuser 5 has a large number of nozzles 5B connected to an air supply pipe 5A arranged at the bottom of the tank main body. Between the air diffuser 5 and the guide wall 3, a current changing plate 6 is provided at an intermediate position in the height direction as a flow reducing device. The current change plate 6 is formed as a plate having a downward inclination angle θ in the flow direction.
[0020]
In the present embodiment, the sewage is purified in the following manner.
[0021]
A mixture of activated sludge containing bacteria and sewage to be purified is introduced into the circuit. By the rotation of the propeller device 4, a circulation flow as shown in FIG. 1 is formed in the circulation path. At this time, the flow turns smoothly due to the presence of the guide wall 3. On the other hand, air is supplied to the air diffuser 5 from the outside via the air supply pipe 5A, and bubbles are generated from the nozzle 5B and rise in the sewage.
[0022]
The circulating flow, which is given a flow velocity by the propeller device 4 and passes through the guide wall 3 of the corner, has a substantially uniform velocity v ₀ in the height direction as shown in FIG. . However, when the circulating flow reaches the current change plate 6, the flow on the bottom side of the tank main body converges and forms a contraction, and the flow velocity distribution in the height direction is v ₁ larger than v ₀ on the lower side, and the above _{v 0} is less than _{v 2} the upper side. That is, it bubbles immediately generated in the diffuser 5 number of bubbles that diameter decreases receives a shearing force by the large flow velocity v ₁ is increased. This means increasing the total contact area of the bubbles with the wastewater. As a result of the bubble is flowed at a greater rate v _1, the time to disappear rise to the liquid surface becomes longer. As described above, since the contact area of the air bubbles with the wastewater is large and the contact time is long, the mixture obtains sufficient oxygen to promote the purification action of the wastewater.
[0023]
The invention is not limited to the illustrated example. For example, the circulating flow generator is not limited to a propeller device, but may be a jet device. In this case, the jetted water may be water, air, or a mixture of water and air. The presence of air also plays a part in the function of the air diffuser. Therefore, it is preferable that the jet device is also located closer to the bottom of the tank body in the height direction, like the propeller device.
[0024]
Next, in the case of the flow reducing device, when it is formed of the above-described current transformer plate, its position and number can be appropriately set according to the operating conditions. The position includes a position in the flow direction of the circulating flow, a position in the height direction and the width direction of the circulation path, and the number can be appropriately set for any of them. In addition, the above-mentioned flow reducing device requires some external energy without depending on the current transformer plate, but it is also possible to use a propeller, a jet, or the like that generates a speed-up flow immediately upstream of the air diffuser. .
[0025]
【The invention's effect】
The present invention provides a current-contracting device at an upstream position of the air diffuser as described above, and a current-distribution plate disposed at an inclination so as to converge the circulating flow between the tank body bottom surface and the downstream side. As a result, the flow on the bottom side of the tank main body can be accelerated at the position of the air diffuser, thereby making it possible to increase the number of bubbles and increase the number of air bubbles, and also to increase the residence time of the air bubbles. improves.
[Brief description of the drawings]
FIG. 1 is a plan view showing a schematic configuration of an apparatus according to an embodiment of the present invention.
FIG. 2 is a view showing a flow velocity distribution in a height direction in the vicinity of a current transformer and an air diffuser of the apparatus of FIG. 1;
[Explanation of symbols]
1 tank body 4 circulating flow generator (propeller device)
5 diffuser 6 contractor (current transformer)

Claims (3)

A tank main body that forms a circulation path at a horizontal level, a circulating flow generator that generates a circulating flow along the circulation path, and an air diffuser that is arranged at the bottom of the tank body and generates rising bubbles in the circulating flow. Yes and, upstream position than the air diffuser, in oxidation ditch system contraction device for converging the flow of the inner tank body bottom side of the circulation flow is disposed in the tank body, contraction device, An oxidation ditch device, characterized in that it is a current change plate arranged at an angle so as to converge a circulating flow with a bottom surface of a tank body toward a downstream side . The oxidation ditch device according to claim 1 , wherein the current change plates are arranged at a plurality of positions in at least one of the direction of the circulation flow, the height direction and the width direction of the circulation path. . Current transformer board oxidation ditch system according to claim 1 or claim 2, that inclination can be changed.

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