JPH0423595B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a deep aeration tank that can effectively utilize limited land and efficiently perform activated sludge treatment of sewage.

(Prior art) Deep aeration tanks with a water depth of over 5 m are used in many sewage treatment plants to improve sewage treatment capacity in restricted areas, but an aeration plate is placed at the bottom of the tank. This requires a blower with high discharge pressure because the head applied to the diffuser plate becomes large, and if the depth of the diffused water exceeds 5 m, a large amount of nitrogen gas in the diffused air will dissolve in the water, so it will be necessary to use a blower in the subsequent process. Nitrogen gas precipitates from the water in the settling tank, and this nitrogen gas adheres to the activated sludge flocs and causes the sludge to rise to the surface.
There was a drawback that the quality of treated water deteriorated. Therefore,
The present applicant has developed a swirling flow type deep tank aeration tank in which the inside of the aeration tank 50 is divided into two by a baffle plate 51 and an aeration plate 52 is provided in the middle part of one of the two, as shown in FIG. This was proposed in Japanese Patent Application No. 59-75633.

(Problem to be Solved by the Invention) However, in a swirling flow type deep aeration tank as shown in Fig. 7, air bubbles riding on the swirling flow rise to the water surface at a higher rate of rise than in still water, so the gas and liquid The contact time was relatively short and it was almost impossible to achieve an oxygen dissolution efficiency of more than 25%. Also,
Attempts have been made to distribute the aeration plates 52 over the entire middle layer of the aeration tank 50 without dividing the aeration tank 50 into two by the full plate 51, but this results in poor exchange of water between the upper and lower layers of the aeration plate 52. However, the bottom of the tank became anaerobic and sludge accumulated.
Therefore, the oxygen dissolution efficiency is high, the water in the entire tank is sufficiently agitated, and there is no accumulation of sludge, and an existing blower with a normal discharge pressure can be used, which prevents the sludge floating phenomenon. A deep aeration tank was needed.

(Means for Solving the Problems) The present invention was completed in order to solve these conventional problems. The plates are set upright at intervals of 0.7 to 0.9 W with respect to the tank width W of the aeration tank to form a wide area surrounded by the buttful plates in the center of the aeration tank, and the middle part of the area is A large number of air diffuser plates are distributed over almost the entire surface, and an upper water guide plate is provided above the baffle plate to smoothly convert upward flow containing air bubbles into downward flow.

Embodiments Next, the present invention will be described in detail with reference to the illustrated embodiments. 1 is an aeration tank having a water depth H of 5 m or more, for example 10 m, and a tank width W of about 0.8 H to 1.2 H;
Reference numerals 2 and 2 designate vertically erected vertical boards near both wall surfaces 3 and 3. The width X between the full plates 2 and 2 is 0.7W to 0.9W, and in this example it is 0.8W.
It is said that These baffle plates 2, 2 form a wide area 4 surrounded by the buffle plates 2 in the center of the aeration tank 1, and this area 4
A large number of air diffusers 5 are uniformly distributed over almost the entire surface of the middle layer. Air was supplied to each diffuser plate 5 from a blower (not shown) and floated up as bubbles, and due to the air lift effect, an upward flow was generated in the area 4, causing the water in the area 4 to rise toward the water surface. Then, it descends toward the bottom of the tank through a downward passage 6 formed in the gap between the buff-full plate 2 and the wall surface 3. Therefore, if the width X between the buttful plates 2, 2 is too wide, the water flow resistance in the descending flow path 6 will increase and the circulation of water in the tank will be inhibited, and if it is too narrow, the aeration area will decrease, Since it is not possible to improve the oxygen dissolution efficiency, which is defined as the amount of oxygen dissolved in water relative to the theoretical amount of oxygen blown into the water from the air diffuser plate 5, from this point of view as well, the width
It is preferable to set it to about 0.9W. In addition, it is desirable that the aeration water depth h be as large as possible in order to provide sufficient contact time between bubbles and water and to improve the oxygen dissolution efficiency and air lift effect.
If the length is 5 m or more, as mentioned above, there is a risk that nitrogen gas will dissolve and float the sludge in the sedimentation tank, so in this embodiment, it is preferably 4 to 5 m. In order to achieve the smoothest circulation in the tank, the upper opening dimension a of the bath full plate 2 should be adjusted.
0.1H to 0.4H, more preferably 0.2H to 0.3H, and a downward flow path 6 is provided at the lower end of the buttful plate 2.
A water guide plate 7 is provided to smoothly convert the downward flow of water into a horizontal flow along the bottom of the tank. 30~ for the bottom corner of the tank
(W-X)/with an angle θ ₁ of 60°, preferably 45°
A chamfered portion 8 having a length l of 4 to (W-X) is formed, and the water guide plate 7 has a portion 7a parallel to this chamfered portion 8.
and a part 7b parallel to the tank bottom, and in order to provide a bottom flow velocity that can prevent sludge accumulation, the distance L from the tank bottom is (W-X)/2 to (W-X), and the wall surface 3 The distance C from the water guide plate 7 to the tip of the water guide plate 7 is set to be W/4 or less in order to prevent a dead zone from being formed on the water guide plate 7. The shape of the water guide plate 7 and the chamfered portion 8 at the bottom corner of the tank may be an arc shape as shown in FIG. 2, and in this case, the radius of curvature of the chamfered portion 8
It is preferable that r ₁ is (W-X)/4 to (W-X). Further, a chevron-shaped central water guiding plate 9 is installed at the center of the tank bottom in order to smoothly convert the flow approaching along the tank bottom from both sides into an upward flow. The angle θ ₂ between the slope and the tank bottom is 30 to 60°, and the horizontal length e of the slope on one side is approximately the same as the length l of the chamfered portion 8 at the corner of the tank bottom. preferable. The central water guide plate 9 may have an arcuate cross _section as shown in _FIG . preferable. Furthermore, the chamfered portion 8 of the bottom corner of the tank is also provided at the top corner of the tank.
A chamfered portion 10 similar to that shown in FIG. The upper water guide plate 11 has a horizontal portion 11a with a length g.
, it is tilted into the water at an angle θ ₃ of 30 to 60° and has a horizontal length f.
The total horizontal length f+g is 0.2W to 0.4W, and f is 0.1W to 0.2W.
It is desirable to do so. This upper water guide plate 11 is for smoothly converting an upward flow containing air bubbles into a downward flow to improve oxygen dissolution efficiency, and is provided with air vent holes 12 throughout the entire surface. Incidentally, the shape of the inclined portion 11b may be an arcuate cross section as shown in FIG.

(Function) With this configuration, air is supplied from the blower to a large number of diffuser plates 5 distributed over almost the entire surface of the middle layer of the region 4 formed in the center of the aeration tank 1. Then, the air becomes bubbles from each diffuser plate 5 and rises in the area 4 surrounded by the baffle plate 2, and due to the air lift effect, a gentle upward flow is generated in the wide area 4, and is thus lifted to the upper part. The water is guided by the upper water guide plate 11 provided below the water surface on the upper part of the baffle plate 2, and descends toward the bottom of the tank from the descending channel 6 formed between the buffle plate 2 and the wall surface 3. However, since this upward flow occurs evenly throughout the wide area 4 surrounded by the baffle plate 2, its rising speed is slow, and there is sufficient air and liquid between it and the bubbles generated from the diffuser plate 5. The contact time is ensured and oxygen dissolution efficiency of far more than 25% can be obtained. Also,
The water lifted to the upper part circulates to the lower part through the downward passage 6 formed between the wall 3 and the baffle plate 2 which is installed upright in the part close to both walls 3 of the aeration tank 1, and then flows to the lower part of the tank. Water throughout the tank is sufficiently agitated and sludge is prevented from accumulating on the bottom of the tank.Moreover, the head applied to the air diffuser plate 5 is smaller than when the air diffuser plate is placed at the bottom of the tank. A blower with a normal discharge pressure can be used, and the surfacing phenomenon of sludge in a sedimentation tank caused by dissolution of nitrogen can also be prevented. The actual measured value of the oxygen dissolution efficiency in the deep aeration tank of the present invention is as shown in the graph of FIG. In response to changes, it shows excellent values as shown by curves A, B, and C. In this graph, curve 2 is the data for the conventional deep aeration tank shown in Figure 7, and curve A is the data for the conventional deep aeration tank shown in Figure 7, and curve A is the data for the conventional deep aeration tank shown in Figure 1. Curve B is the data for the case where water guide plate 7 and center water guide plate 9 are added to it, and curve C is the data for the deep tank aeration tank as shown in Fig. 1 in which the upper water guide plate 11 is further added. be. As described above, according to the present invention, the oxygen dissolution efficiency is improved by about 10 to 20% compared to the conventional method. Further, FIG. 6 shows the relationship between the air blowing rate and the flow velocity at the bottom of the tank, and curves A, B, and C are measured values under the same conditions as explained in FIG. 5. According to the present invention, the bottom flow velocity is 10 cm/cm, which is said to be the critical flow velocity that can prevent sludge accumulation.
sec can be easily exceeded, and the accumulation of sludge on the tank bottom can be sufficiently prevented.

(Effects of the Invention) As is clear from the above explanation, the present invention has an oxygen dissolution efficiency that is approximately 10 to 20% higher than that of the conventional method, and therefore accounts for 40 to 20% of the power consumption of the entire sewage treatment plant.
The power consumption of the aeration tank, which accounts for 50%, can be significantly reduced, and the water circulation throughout the tank is sufficient, eliminating the accumulation of sludge, and a blower with normal discharge pressure can be used. , sludge floating phenomenon in the sedimentation area does not occur. Therefore, the present invention greatly contributes to the development of industry as it solves the problems of conventional deep aeration tanks.

[Brief explanation of drawings]

Fig. 1 is a vertical sectional view showing an embodiment of the present invention, Fig. 2
The figure is a longitudinal sectional view showing a modification of the bottom corner of the tank, FIG. 3 is a longitudinal sectional view showing a modification of the central water guiding plate, FIG. 4 is a longitudinal sectional view showing a modification of the upper water guiding plate, and FIG. 6 is a graph showing the relationship between air blowing rate and oxygen dissolution efficiency, FIG. 6 is a graph showing the relationship between air blowing rate and bottom flow velocity, and FIG. 7 is a longitudinal cross-sectional view of a conventional deep aeration tank. 1: Aeration tank, 2: Full plate, 3: Wall surface, 4:
Area, 5: Diffuser plate.

Claims (1)

[Claims] 1 Both walls 3 of the aeration tank 1 with a water depth of 5 m or more
Vertical butt-full plates 2 are erected near the part close to the tank width W of the aeration tank 1 with an interval of 0.7 to 0.9W to create a wide area surrounded by the butt-full plates 2 in the center of the aeration tank 1. 4, a large number of air diffusers 5 are distributed over almost the entire surface of the middle layer in the area 4, and an upper water guide is provided above the baffle plate 2 to smoothly convert the upward flow containing air bubbles into a downward flow. A deep aeration tank characterized by being provided with a plate 11.