JPH06262195A - Deep layer aeration tank - Google Patents

Abstract

PURPOSE:To maintain efficiency of oxygen dissolution at a high level by increasing the velocity of downward water flow in a downward tube installed in the aeration tank by utilizing the water lifting power of an oxygen supplying and water lifting means, thereby feeding air bubbles down into a deep layer part. CONSTITUTION:This deep layer aeration tank 10 is internally provided with the downward tube 11 which arrives at the deep layer part, an aeration section 13 which has the oxygen supplying and water lifting means 20 provided at least above the middle layer part in the tank, a reaction chamber 16 which has a reaction section in a part exclusive of the part segmented with the downward tube 11 and the aeration part 13 and a suction tube 14 which is provided with a diving dike 18 in the upper layer part between this reaction chamber 16 and the aeration section 13 and communicates with the lower part of the aeration part 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deep aeration tank capable of efficiently supplying oxygen in a deep aeration tank in which organic substances and nitrogen contained in an organic waste liquid are oxidatively decomposed by using aerobic microorganisms.

[0002]

2. Description of the Related Art Regarding aeration tanks for biologically treating waste liquid containing organic substances and nitrogen, in order to effectively use the site,
A deep aeration tank has been proposed, which can replace a conventional aeration tank with a shallow water depth and can dig deep into the ground to increase the amount of treatment liquid stored. The conventional means for supplying oxygen to the deep layer in the deep aeration tank is to arrange a diffuser plate or a submersible mechanical aerator at an intermediate water level (for example, a water depth of about 5 m) to create a circulating water flow. A device provided with a tube or a baffle plate is known. Since such a conventional system cannot dissolve air efficiently, the one disclosed in JP-A-3-137993 has been proposed as an example of a means for improving this. In addition to this, a draft tube is installed in the tank, an air diffuser is placed in this draft tube, and stirring blades are placed to finely diffuse the supply air and at the same time put it on the water flow and push it into the deep part to create a circulating water flow. The scheme is also known.

[0003]

However, in the air diffusion method used in the conventional deep aeration tank, the sent air is short-circuited and is easily released to the atmosphere in the upper part of the tank, and the contact between air and liquid is caused. The time is short and the dissolution efficiency of oxygen is only about 20%. Further, in the method according to the above-mentioned publication, which was devised to improve the dissolution efficiency of oxygen as compared with the conventional method,
If a compressor or the like is used as a means for supplying oxygen, the efficiency is poor and the operating cost is high, which is economically difficult.
In addition, the method of rotating the stirring blade in the draft tube inevitably raises the operating cost.

The present invention solves these problems and
In order to increase the dissolution efficiency of oxygen to the liquid, the submerged mechanical aerator or the combination of the submersible pump with the submersible oxygen supply pump is used in the tank by using the pumping power of the pumping means. It is an object of the present invention to provide a deep aeration tank capable of maintaining the water flow faster than the ascending speed of diffused bubbles and feeding the bubbles to the deep layer to maintain a high oxygen dissolution efficiency and improving the economical efficiency.

[0005]

The deep aeration tank of the present invention configured to achieve such an object comprises a downward tube reaching the deep portion inside the aeration tank, and at least a middle layer portion in the tank. From the aeration part provided with oxygen supply pumping means provided above, a reaction tank other than the part partitioned by the downward tube and the aeration part, and the reaction tank and the aeration part. A submerged weir is provided in the upper part of the space, and a suction tube communicating with the lower part of the aeration part is provided.

[0006]

In the deep aeration tank of the present invention constructed as described above, the downward flow velocity in the adjacent downward tube is made faster than the ascending velocity of bubbles by utilizing the pumping power of the oxygen supply pumping means provided in the aeration part. By forming a flow path so that it can be retained and sending bubbles to the deep layer, it is possible to effectively use the previously diffused air that was released to the atmosphere in a short time without adding additional power and oxygen. It becomes possible to maintain high dissolution efficiency, and efficient treatment can be achieved without increasing operating costs.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the deep aeration tank of the present invention will be described below with reference to the drawings. First, FIG. 1 is a flow sheet showing an experimental apparatus for obtaining the deep aeration tank of the present invention. This device is a water tank 1 having a width of 510 mm, a height of 5000 mm, and a thickness of 120 mm, and the inside of this water tank 1 is divided into three compartments at the size ratios shown in the figure, and an aeration chamber 2 and a downward tube 3 are provided. And an L-shaped compartment 4 which is deeper than these two compartments and communicates with the lower side of these compartments. An air diffuser 5 is arranged in the aeration chamber 2, and an upper portion of the aeration chamber 2 is connected to the aeration chamber 2 via a circulation pump 6 from a compartment 4 which is open to the atmosphere and is connected to the lower side of the aeration chamber 2. Then, air pressurized by the aeration blower 7 is supplied from the outside of the water tank 1 to the diffuser 5 provided in the aeration chamber 2, and the upper portion of the aeration chamber 2 is driven by the water flow driven by the circulation pump 6. Utilizing the water head generated in the above, the flow velocity of the downward water flow generated in the downward tube 3 is used to send a part of the bubbles in the aeration chamber 2 to the inner bottom of the compartment 4. The upper communication portion of the aeration chamber 2 and the downward tube 3 and the upper portion of the L-shaped compartment 4 are partitioned and closed, and gas outlets are provided in each of them, and a wet gas meter is provided through each of these gas outlets. 7a, 7
It is connected to b and 7c.

In this experimental apparatus, the flow rate of water is measured by a flow meter 8 provided in a pipe connected to the circulation pump 6, and the amount of air supplied, the amount of air released to the atmosphere, and the inner bottom of the water tank (inner bottom of compartment 4). The amount of air sent to the wet gas meters 7a, 7b, 7c (reference numeral 7a is a gas meter for measuring the amount of air sent, 7b is a gas meter for measuring the amount released to the atmosphere, and 7c is the amount of air recycled). Gas meter). The experimental results using this experimental apparatus are shown in the graph of FIG.

In the above experimental apparatus, the flow velocity in the downward tube 3 was varied (0.25 m / sec, 0.3 m / se).
c, 0.35 m / sec, 0.4 m / sec) and the air intake rate (volume of bubbles sent to the bottom by water flow /
An experiment was conducted to confirm the relationship between the air supply rate to the diffuser) and the gas superficial velocity (air supply rate to the diffuser / cross-sectional area of the chamber). As a result, the downward flow velocity in the downward tube 3 is 0.
At 3 m / sec or more, the air suction rate increases as the downward flow velocity increases. Then, the standard bubble diameter (2-
4 mm diameter), the flow velocity in the downward tube 3 is 0.4 m /
It was found that an air suction rate of 25% or more can be obtained under the condition of sec. Further, the air suction rate tends to increase as the gas superficial velocity increases, but the increasing tendency gradually decreases from a certain point, and the gas superficial velocity 0.007 NL / m 2 · sec at the downward flow velocity in the downward tube 3. Became the limit value. Therefore, the downward tube 3
The downward flow velocity in the inside is increased to draw in a part of the air bubbles of the air diffused from the diffuser 5 into the aeration chamber 2 and send the air to the inner bottom of the compartment 4 to increase the time for the bubbles to rise in the compartment 4. It has been confirmed that the rate of dissolution in water can be increased.

Therefore, the present inventors have obtained the deep aeration tank shown in FIG. 3 as a result of various studies based on the above-mentioned experiments. In FIG. 3, the deep aeration tank 10 has a downwardly facing tube 11 formed by a partition wall 12 provided by shifting the inside of the deeply aerated tank 10 to one side in the lengthwise direction (left and right direction in the drawing). An aeration portion 13 is provided adjacent to the suction tube 14 and a suction tube 14 is provided at a position opposite to the downward tube 11 of the aeration portion 13 so as to communicate with a bottom portion of the aeration portion 13 through a suction port 19. It is provided by being partitioned by the other part and the partition wall 15. The inside of the tank other than the downward tube 11, the aeration portion 13 and the suction tube 14 is configured to be a reaction tank 16.

The upper part of the aeration part 13 and the downward tube 11
The upper portion of the partition wall 12 is appropriately dimensioned lower than the standard water level so that the partition wall 12 communicates. Also, the downward tube 1
The lower end of 1 communicates with the bottom of the reaction tank 16. Further, the aeration part 13 and the upper part of the reaction tank 16 are separated by a partition wall 17
Completely blocked by. The suction tube 14 connecting the upper part of the reaction tank 16 and the bottom of the aeration part 13 is connected to the upper part of the reaction tank 16 by a submerged weir 18 whose size is appropriately lowered from the standard water level.

In the deep aeration tank 10 having such a cross-sectional structure, the inner bottom portion of the aeration portion 13 (for example, water depth 4-5).
m) is provided with an oxygen supply pumping means 20 (for example, a known submersible mechanical aerator or a combination of an underwater pump and a diffuser), and compressed air is supplied from the upper part of the tank to the oxygen supply pumping means 20 by an air pipe 21. It is designed to be powered by.
Even when a combination of a submersible pump and an air diffuser is adopted for the oxygen supply pumping means 20, the submersible pump has a downward water flow velocity of about 0.4 m / sec in the downward tube 11 when pumping water. It is preferable to adopt one having the following ability.

In the deep aeration tank 10 of the present invention thus constructed, the oxygen supply pumping means 20 is operated to dissolve oxygen in the liquid as in the conventional aeration tank having a shallow water depth. At this time, the pumping force by the operation of the oxygen supply pumping means 20 and the lift of the diffused bubbles cause a downward water flow in the downward tube 11 and increase its flow velocity, and the water flow causes the air to float at the aeration portion 13. A part of the air bubbles thus diffused is forcibly transferred through the downward tube 11 to the bottom of the tank and sent out into the reaction tank 16. Then, the liquid containing the bubbles sent into the reaction tank 16 has a low flow velocity, and while the bubbles sent from the deep water position slowly rise, the oxygen is dissolved in the liquid to dissolve the oxygen. The rate can be increased.

Then, the liquid in the reaction tank 16 side is sucked into the aeration part 13 through the suction tube 14 from the suction port 19 opened at the bottom of the aeration part 13 by the operation of the oxygen supply pumping means 20 described above. , This reaction tank 16
The liquid inside is sequentially pumped up, passed through the downward tube 11 and sent to the bottom of the reaction tank 16 for circulation. Further, the scum generated in the upper portion of the reaction tank 16 is removed by suction at the submerged weir 18 portion without stagnation in the upper layer due to the water flow sucked by the suction tube 14.

The deep aeration tank 10 thus constructed
In addition to the oxygen utilization efficiency (about 20%) by the conventional air diffuser, 25% or more of the bubbles containing about 80% oxygen that was diffused into the atmosphere in the past were deeply aerated without adding new energy. Oxygen dissolution efficiency of 30 by sending to the bottom of the tank
It becomes possible to raise it to more than%. Therefore, oxygen necessary for respiration and metabolism of the microorganisms existing in the liquid, even though it is in a deep layer, is replenished to accelerate the oxidative decomposition treatment of organic substances and the like.

[0016]

As described above, according to the present invention, the conventional aeration method is used as it is, and the lift force of the oxygen supply pumping means is used to add bubbles to the deep aeration tank without adding new energy. By feeding it to the bottom, the oxygen dissolution efficiency can be further increased, which can be useful for reducing the operating cost.

[Brief description of drawings]

FIG. 1 is a flow sheet diagram showing an experimental apparatus for obtaining a deep layer aeration tank of the present invention.

FIG. 2 is a graph showing the relationship between the gas superficial velocity of the aeration tank and the air suction rate in the experiment of the present invention.

FIG. 3 is a view showing a sectional structure of a deep layer aeration tank for carrying out the present invention.

[Explanation of symbols]

 10 Deep Aeration Tank 11 Downward Tube 12,17 Partition Wall 13 Aeration Part 14 Suction Tube 15 Partition Wall 16 Reaction Tank 20 Oxygen Supply Pumping Means

Claims (1)

[Claims] 1. A downward tube reaching a deep layer inside an aeration tank, an aeration section provided with an oxygen supply pumping means provided above at least a middle layer section in the tank, the downward tube and the aeration section. A reaction tank having a reaction part other than the part partitioned by, and a suction tube that communicates with the lower part of the aeration part by providing a submerged weir in the upper part between the reaction tank and the aeration part. A deep aeration tank characterized by the presence of